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From ka...@apache.org
Subject [15/31] Rearrange website directory structure
Date Thu, 02 Jan 2014 00:14:15 GMT
http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/Quickstart.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+<head>
+  <title>Quickstart</title>
+</head>
+
+Quickstart
+---------
+
+Get Helix
+---------
+
+First, let\'s get Helix. Either build it, or download it.
+
+### Build
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout tags/helix-0.7.0-incubating
+mvn install package -DskipTests
+# This folder contains quickstart.sh and start-helix-participant.sh
+cd helix-examples/target/helix-examples-pkg/bin
+chmod +x *
+# This folder contains helix-admin.sh, start-standalone-zookeeper.sh, and run-helix-controller.sh
+cd ../../../../helix-core/target/helix-core-pkg/bin
+```
+
+### Download
+
+Download the 0.7.0-incubating release package [here](./download.html)
+
+Overview
+--------
+
+In this Quickstart, we\'ll set up a master-slave replicated, partitioned system.  Then we\'ll demonstrate how to add a node, rebalance the partitions, and show how Helix manages failover.
+
+
+Let\'s Do It
+------------
+
+Helix provides command line interfaces to set up the cluster and view the cluster state. The best way to understand how Helix views a cluster is to build a cluster.
+
+### Get to the Tools Directory
+
+If you built the code:
+
+```
+cd helix/incubator-helix/helix-examples/target/helix-examples-pkg/bin
+```
+
+If you downloaded the release package, extract it.
+
+
+Short Version
+-------------
+You can observe the components working together in this demo, which does the following:
+
+* Create a cluster
+* Add 2 nodes (participants) to the cluster
+* Set up a resource with 6 partitions and 2 replicas: 1 Master, and 1 Slave per partition
+* Show the cluster state after Helix balances the partitions
+* Add a third node
+* Show the cluster state.  Note that the third node has taken mastership of 2 partitions.
+* Kill the third node (Helix takes care of failover)
+* Show the cluster state.  Note that the two surviving nodes take over mastership of the partitions from the failed node
+
+### Run the Demo
+
+```
+cd helix/incubator-helix/helix-examples/target/helix-examples-pkg/bin
+./quickstart.sh
+```
+
+#### The Initial Setup
+
+2 nodes are set up and the partitions are rebalanced.
+
+The cluster state is as follows:
+
+```
+CLUSTER STATE: After starting 2 nodes
+                localhost_12000    localhost_12001
+MyResource_0           M                  S
+MyResource_1           S                  M
+MyResource_2           M                  S
+MyResource_3           M                  S
+MyResource_4           S                  M
+MyResource_5           S                  M
+```
+
+Note there is one master and one slave per partition.
+
+#### Add a Node
+
+A third node is added and the cluster is rebalanced.
+
+The cluster state changes to:
+
+```
+CLUSTER STATE: After adding a third node
+               localhost_12000    localhost_12001    localhost_12002
+MyResource_0          S                  M                  S
+MyResource_1          S                  S                  M
+MyResource_2          M                  S                  S
+MyResource_3          S                  S                  M
+MyResource_4          M                  S                  S
+MyResource_5          S                  M                  S
+```
+
+Note there is one master and _two_ slaves per partition.  This is expected because there are three nodes.
+
+#### Kill a Node
+
+Finally, a node is killed to simulate a failure
+
+Helix makes sure each partition has a master.  The cluster state changes to:
+
+```
+CLUSTER STATE: After the 3rd node stops/crashes
+               localhost_12000    localhost_12001    localhost_12002
+MyResource_0          S                  M                  -
+MyResource_1          S                  M                  -
+MyResource_2          M                  S                  -
+MyResource_3          M                  S                  -
+MyResource_4          M                  S                  -
+MyResource_5          S                  M                  -
+```
+
+
+Long Version
+------------
+Now you can run the same steps by hand.  In this detailed version, we\'ll do the following:
+
+* Define a cluster
+* Add two nodes to the cluster
+* Add a 6-partition resource with 1 master and 2 slave replicas per partition
+* Verify that the cluster is healthy and inspect the Helix view
+* Expand the cluster: add a few nodes and rebalance the partitions
+* Failover: stop a node and verify the mastership transfer
+
+### Install and Start ZooKeeper
+
+Zookeeper can be started in standalone mode or replicated mode.
+
+More information is available at
+
+* http://zookeeper.apache.org/doc/r3.3.3/zookeeperStarted.html
+* http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html#sc_zkMulitServerSetup
+
+In this example, let\'s start zookeeper in local mode.
+
+#### Start ZooKeeper Locally on Port 2199
+
+```
+./start-standalone-zookeeper.sh 2199 &
+```
+
+### Define the Cluster
+
+The helix-admin tool is used for cluster administration tasks. In the Quickstart, we\'ll use the command line interface. Helix supports a REST interface as well.
+
+zookeeper_address is of the format host:port e.g localhost:2199 for standalone or host1:port,host2:port for multi-node.
+
+Next, we\'ll set up a cluster MYCLUSTER cluster with these attributes:
+
+* 3 instances running on localhost at ports 12913,12914,12915
+* One database named myDB with 6 partitions
+* Each partition will have 3 replicas with 1 master, 2 slaves
+* ZooKeeper running locally at localhost:2199
+
+#### Create the Cluster MYCLUSTER
+
+```
+# ./helix-admin.sh --zkSvr <zk_address> --addCluster <clustername>
+./helix-admin.sh --zkSvr localhost:2199 --addCluster MYCLUSTER
+```
+
+### Add Nodes to the Cluster
+
+In this case we\'ll add three nodes: localhost:12913, localhost:12914, localhost:12915
+
+```
+# helix-admin.sh --zkSvr <zk_address>  --addNode <clustername> <host:port>
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12913
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12914
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12915
+```
+
+### Define the Resource and Partitioning
+
+In this example, the resource is a database, partitioned 6 ways. Note that in a production system, it\'s common to over-partition for better load balancing.  Helix has been used in production to manage hundreds of databases each with 10s or 100s of partitions running on 10s of physical nodes.
+
+#### Create a Database with 6 Partitions using the MasterSlave State Model
+
+Helix ensures there will be exactly one master for each partition.
+
+```
+# helix-admin.sh --zkSvr <zk_address> --addResource <clustername> <resourceName> <numPartitions> <StateModelName>
+./helix-admin.sh --zkSvr localhost:2199 --addResource MYCLUSTER myDB 6 MasterSlave
+```
+
+#### Let Helix Assign Partitions to Nodes
+
+This command will distribute the partitions amongst all the nodes in the cluster. In this example, each partition has 3 replicas.
+
+```
+# helix-admin.sh --zkSvr <zk_address> --rebalance <clustername> <resourceName> <replication factor>
+./helix-admin.sh --zkSvr localhost:2199 --rebalance MYCLUSTER myDB 3
+```
+
+Now the cluster is defined in ZooKeeper.  The nodes (localhost:12913, localhost:12914, localhost:12915) and resource (myDB, with 6 partitions using the MasterSlave model) are all properly configured.  And the _IdealState_ has been calculated, assuming a replication factor of 3.
+
+### Start the Helix Controller
+
+Now that the cluster is defined in ZooKeeper, the Helix controller can manage the cluster.
+
+```
+# Start the cluster manager, which will manage MYCLUSTER
+./run-helix-controller.sh --zkSvr localhost:2199 --cluster MYCLUSTER 2>&1 > /tmp/controller.log &
+```
+
+### Start up the Cluster to be Managed
+
+We\'ve started up ZooKeeper, defined the cluster, the resources, the partitioning, and started up the Helix controller.  Next, we\'ll start up the nodes of the system to be managed.  Each node is a Participant, which is an instance of the system component to be managed.  Helix assigns work to Participants, keeps track of their roles and health, and takes action when a node fails.
+
+```
+# start up each instance.  These are mock implementations that are actively managed by Helix
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12913 --stateModelType MasterSlave 2>&1 > /tmp/participant_12913.log
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12914 --stateModelType MasterSlave 2>&1 > /tmp/participant_12914.log
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12915 --stateModelType MasterSlave 2>&1 > /tmp/participant_12915.log
+```
+
+### Inspect the Cluster
+
+Now, let\'s see the Helix view of our cluster.  We\'ll work our way down as follows:
+
+```
+Clusters -> MYCLUSTER -> instances -> instance detail
+                      -> resources -> resource detail
+                      -> partitions
+```
+
+A single Helix controller can manage multiple clusters, though so far, we\'ve only defined one cluster.  Let\'s see:
+
+```
+# List existing clusters
+./helix-admin.sh --zkSvr localhost:2199 --listClusters
+
+Existing clusters:
+MYCLUSTER
+```
+
+Now, let\'s see the Helix view of MYCLUSTER:
+
+```
+# helix-admin.sh --zkSvr <zk_address> --listClusterInfo <clusterName>
+./helix-admin.sh --zkSvr localhost:2199 --listClusterInfo MYCLUSTER
+
+Existing resources in cluster MYCLUSTER:
+myDB
+Instances in cluster MYCLUSTER:
+localhost_12915
+localhost_12914
+localhost_12913
+```
+
+Let\'s look at the details of an instance:
+
+```
+# ./helix-admin.sh --zkSvr <zk_address> --listInstanceInfo <clusterName> <InstanceName>
+./helix-admin.sh --zkSvr localhost:2199 --listInstanceInfo MYCLUSTER localhost_12913
+
+InstanceConfig: {
+  "id" : "localhost_12913",
+  "mapFields" : {
+  },
+  "listFields" : {
+  },
+  "simpleFields" : {
+    "HELIX_ENABLED" : "true",
+    "HELIX_HOST" : "localhost",
+    "HELIX_PORT" : "12913"
+  }
+}
+```
+
+
+#### Query Information about a Resource
+
+```
+# helix-admin.sh --zkSvr <zk_address> --listResourceInfo <clusterName> <resourceName>
+./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB
+
+IdealState for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_1" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "MASTER"
+    },
+    "myDB_4" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+    "myDB_0" : [ "localhost_12914", "localhost_12913", "localhost_12915" ],
+    "myDB_1" : [ "localhost_12915", "localhost_12913", "localhost_12914" ],
+    "myDB_2" : [ "localhost_12913", "localhost_12915", "localhost_12914" ],
+    "myDB_3" : [ "localhost_12915", "localhost_12913", "localhost_12914" ],
+    "myDB_4" : [ "localhost_12913", "localhost_12914", "localhost_12915" ],
+    "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ]
+  },
+  "simpleFields" : {
+    "IDEAL_STATE_MODE" : "AUTO",
+    "REBALANCE_MODE" : "SEMI_AUTO",
+    "NUM_PARTITIONS" : "6",
+    "REPLICAS" : "3",
+    "STATE_MODEL_DEF_REF" : "MasterSlave",
+    "STATE_MODEL_FACTORY_NAME" : "DEFAULT"
+  }
+}
+
+ExternalView for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_1" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "MASTER"
+    },
+    "myDB_4" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12914" : "SLAVE",
+      "localhost_12915" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+  },
+  "simpleFields" : {
+    "BUCKET_SIZE" : "0"
+  }
+}
+```
+
+Now, let\'s look at one of the partitions:
+
+```
+# helix-admin.sh --zkSvr <zk_address> --listResourceInfo <clusterName> <partition>
+./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo mycluster myDB_0
+```
+
+### Expand the Cluster
+
+Next, we\'ll show how Helix does the work that you\'d otherwise have to build into your system.  When you add capacity to your cluster, you want the work to be evenly distributed.  In this example, we started with 3 nodes, with 6 partitions.  The partitions were evenly balanced, 2 masters and 4 slaves per node. Let\'s add 3 more nodes: localhost:12916, localhost:12917, localhost:12918
+
+```
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12916
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12917
+./helix-admin.sh --zkSvr localhost:2199  --addNode MYCLUSTER localhost:12918
+```
+
+And start up these instances:
+
+```
+# start up each instance.  These are mock implementations that are actively managed by Helix
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12916 --stateModelType MasterSlave 2>&1 > /tmp/participant_12916.log
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12917 --stateModelType MasterSlave 2>&1 > /tmp/participant_12917.log
+./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12918 --stateModelType MasterSlave 2>&1 > /tmp/participant_12918.log
+```
+
+
+And now, let Helix do the work for you.  To shift the work, simply rebalance.  After the rebalance, each node will have one master and two slaves.
+
+```
+./helix-admin.sh --zkSvr localhost:2199 --rebalance MYCLUSTER myDB 3
+```
+
+### View the Cluster
+
+OK, let\'s see how it looks:
+
+
+```
+./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB
+
+IdealState for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12917" : "MASTER"
+    },
+    "myDB_1" : {
+      "localhost_12916" : "SLAVE",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12915" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_4" : {
+      "localhost_12916" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+    "myDB_0" : [ "localhost_12917", "localhost_12913", "localhost_12914" ],
+    "myDB_1" : [ "localhost_12918", "localhost_12917", "localhost_12916" ],
+    "myDB_2" : [ "localhost_12913", "localhost_12917", "localhost_12918" ],
+    "myDB_3" : [ "localhost_12915", "localhost_12917", "localhost_12918" ],
+    "myDB_4" : [ "localhost_12916", "localhost_12917", "localhost_12918" ],
+    "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ]
+  },
+  "simpleFields" : {
+    "IDEAL_STATE_MODE" : "AUTO",
+    "REBALANCE_MODE" : "SEMI_AUTO",
+    "NUM_PARTITIONS" : "6",
+    "REPLICAS" : "3",
+    "STATE_MODEL_DEF_REF" : "MasterSlave",
+    "STATE_MODEL_FACTORY_NAME" : "DEFAULT"
+  }
+}
+
+ExternalView for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12917" : "MASTER"
+    },
+    "myDB_1" : {
+      "localhost_12916" : "SLAVE",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12915" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_4" : {
+      "localhost_12916" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+  },
+  "simpleFields" : {
+    "BUCKET_SIZE" : "0"
+  }
+}
+```
+
+Mission accomplished.  The partitions are nicely balanced.
+
+### How about Failover?
+
+Building a fault tolerant system isn\'t trivial, but with Helix, it\'s easy.  Helix detects a failed instance, and triggers mastership transfer automatically.
+
+First, let's fail an instance.  In this example, we\'ll kill localhost:12918 to simulate a failure.
+
+We lost localhost:12918, so myDB_1 lost its MASTER.  Helix can fix that, it will transfer mastership to a healthy node that is currently a SLAVE, say localhost:12197.  Helix balances the load as best as it can, given there are 6 partitions on 5 nodes.  Let\'s see:
+
+
+```
+./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB
+
+IdealState for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12917" : "MASTER"
+    },
+    "myDB_1" : {
+      "localhost_12916" : "SLAVE",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12915" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_4" : {
+      "localhost_12916" : "MASTER",
+      "localhost_12917" : "SLAVE",
+      "localhost_12918" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+    "myDB_0" : [ "localhost_12917", "localhost_12913", "localhost_12914" ],
+    "myDB_1" : [ "localhost_12918", "localhost_12917", "localhost_12916" ],
+    "myDB_2" : [ "localhost_12913", "localhost_12918", "localhost_12917" ],
+    "myDB_3" : [ "localhost_12915", "localhost_12918", "localhost_12917" ],
+    "myDB_4" : [ "localhost_12916", "localhost_12917", "localhost_12918" ],
+    "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ]
+  },
+  "simpleFields" : {
+    "IDEAL_STATE_MODE" : "AUTO",
+    "REBALANCE_MODE" : "SEMI_AUTO",
+    "NUM_PARTITIONS" : "6",
+    "REPLICAS" : "3",
+    "STATE_MODEL_DEF_REF" : "MasterSlave",
+    "STATE_MODEL_FACTORY_NAME" : "DEFAULT"
+  }
+}
+
+ExternalView for myDB:
+{
+  "id" : "myDB",
+  "mapFields" : {
+    "myDB_0" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "SLAVE",
+      "localhost_12917" : "MASTER"
+    },
+    "myDB_1" : {
+      "localhost_12916" : "SLAVE",
+      "localhost_12917" : "MASTER"
+    },
+    "myDB_2" : {
+      "localhost_12913" : "MASTER",
+      "localhost_12917" : "SLAVE"
+    },
+    "myDB_3" : {
+      "localhost_12915" : "MASTER",
+      "localhost_12917" : "SLAVE"
+    },
+    "myDB_4" : {
+      "localhost_12916" : "MASTER",
+      "localhost_12917" : "SLAVE"
+    },
+    "myDB_5" : {
+      "localhost_12913" : "SLAVE",
+      "localhost_12914" : "MASTER",
+      "localhost_12915" : "SLAVE"
+    }
+  },
+  "listFields" : {
+  },
+  "simpleFields" : {
+    "BUCKET_SIZE" : "0"
+  }
+}
+```
+
+As we\'ve seen in this Quickstart, Helix takes care of partitioning, load balancing, elasticity, failure detection and recovery.
+
+### ZooInspector
+
+You can view all of the underlying data by going direct to zookeeper.  Use ZooInspector that comes with zookeeper to browse the data. This is a java applet (make sure you have X windows)
+
+To start zooinspector run the following command from <zk_install_directory>/contrib/ZooInspector
+
+```
+java -cp zookeeper-3.3.3-ZooInspector.jar:lib/jtoaster-1.0.4.jar:../../lib/log4j-1.2.15.jar:../../zookeeper-3.3.3.jar org.apache.zookeeper.inspector.ZooInspector
+```
+
+### Next
+
+Now that you understand the idea of Helix, read the [tutorial](./Tutorial.html) to learn how to choose the right state model and constraints for your system, and how to implement it.  In many cases, the built-in features meet your requirements.  And best of all, Helix is a customizable framework, so you can plug in your own behavior, while retaining the automation provided by Helix.
+

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/Tutorial.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+<head>
+  <title>Tutorial</title>
+</head>
+
+# Helix Tutorial
+
+In this tutorial, we will cover the roles of a Helix-managed cluster, and show the code you need to write to integrate with it.  In many cases, there is a simple default behavior that is often appropriate, but you can also customize the behavior.
+
+Convention: we first cover the _basic_ approach, which is the easiest to implement.  Then, we'll describe _advanced_ options, which give you more control over the system behavior, but require you to write more code.
+
+
+### Prerequisites
+
+1. Read [Concepts/Terminology](../Concepts.html) and [Architecture](../Architecture.html)
+2. Read the [Quickstart guide](./Quickstart.html) to learn how Helix models and manages a cluster
+3. Install Helix source.  See: [Quickstart](./Quickstart.html) for the steps.
+
+### Tutorial Outline
+
+1. [Participant](./tutorial_participant.html)
+2. [Spectator](./tutorial_spectator.html)
+3. [Controller](./tutorial_controller.html)
+4. [Rebalancing Algorithms](./tutorial_rebalance.html)
+5. [User-Defined Rebalancing](./tutorial_user_def_rebalancer.html)
+6. [State Machines](./tutorial_state.html)
+7. [Messaging](./tutorial_messaging.html)
+8. [Customized health check](./tutorial_health.html)
+9. [Throttling](./tutorial_throttling.html)
+10. [Application Property Store](./tutorial_propstore.html)
+11. [Logical Accessors](./tutorial_accessors.html)
+12. [Admin Interface](./tutorial_admin.html)
+13. [YAML Cluster Setup](./tutorial_yaml.html)
+
+### Preliminaries
+
+First, we need to set up the system.  Let\'s walk through the steps in building a distributed system using Helix. We will show how to do this using both the Java admin interface, as well as the [cluster accessor](./tutorial_accessors.html) interface. You can choose either interface depending on which most closely matches your needs.
+
+#### Start ZooKeeper
+
+This starts a zookeeper in standalone mode. For production deployment, see [Apache ZooKeeper](http://zookeeper.apache.org) for instructions.
+
+```
+./start-standalone-zookeeper.sh 2199 &
+```
+
+#### Create a Cluster
+
+Creating a cluster will define the cluster in appropriate ZNodes on ZooKeeper.
+
+Using the Java accessor API:
+
+```
+// Note: ZK_ADDRESS is the host:port of Zookeeper
+String ZK_ADDRESS = "localhost:2199";
+HelixConnection connection = new ZKHelixConnection(ZK_ADDRESS);
+
+ClusterId clusterId = ClusterId.from("helix-demo");
+ClusterAccessor clusterAccessor = connection.createClusterAccessor(clusterId);
+ClusterConfig clusterConfig = new ClusterConfig.Builder(clusterId).build();
+clusterAccessor.createCluster(clusterConfig);
+```
+
+OR
+
+Using the HelixAdmin Java interface:
+
+```
+// Create setup tool instance
+// Note: ZK_ADDRESS is the host:port of Zookeeper
+String ZK_ADDRESS = "localhost:2199";
+HelixAdmin admin = new ZKHelixAdmin(ZK_ADDRESS);
+
+String CLUSTER_NAME = "helix-demo";
+//Create cluster namespace in zookeeper
+admin.addCluster(CLUSTER_NAME);
+```
+
+OR
+
+Using the command-line interface:
+
+```
+./helix-admin.sh --zkSvr localhost:2199 --addCluster helix-demo
+```
+
+
+#### Configure the Nodes of the Cluster
+
+First we\'ll add new nodes to the cluster, then configure the nodes in the cluster. Each node in the cluster must be uniquely identifiable.
+The most commonly used convention is hostname_port.
+
+```
+int NUM_NODES = 2;
+String hosts[] = new String[]{"localhost","localhost"};
+int ports[] = new int[]{7000,7001};
+for (int i = 0; i < NUM_NODES; i++)
+{
+  ParticipantId participantId = ParticipantId.from(hosts[i] + "_" + ports[i]);
+
+  // set additional configuration for the participant; these can be accessed during node start up
+  UserConfig userConfig = new UserConfig(Scope.participant(participantId));
+  userConfig.setSimpleField("key", "value");
+
+  // configure and add the participant
+  ParticipantConfig participantConfig = new ParticipantConfig.Builder(participantId)
+      .hostName(hosts[i]).port(ports[i]).enabled(true).userConfig(userConfig).build();
+  clusterAccessor.addParticipantToCluster(participantConfig);
+}
+```
+
+OR
+
+Using the HelixAdmin Java interface:
+
+```
+String CLUSTER_NAME = "helix-demo";
+int NUM_NODES = 2;
+String hosts[] = new String[]{"localhost","localhost"};
+String ports[] = new String[]{7000,7001};
+for (int i = 0; i < NUM_NODES; i++)
+{
+  InstanceConfig instanceConfig = new InstanceConfig(hosts[i] + "_" + ports[i]);
+  instanceConfig.setHostName(hosts[i]);
+  instanceConfig.setPort(ports[i]);
+  instanceConfig.setInstanceEnabled(true);
+
+  //Add additional system specific configuration if needed. These can be accessed during the node start up.
+  instanceConfig.getRecord().setSimpleField("key", "value");
+  admin.addInstance(CLUSTER_NAME, instanceConfig);
+}
+```
+
+#### Configure the Resource
+
+A _resource_ represents the actual task performed by the nodes. It can be a database, index, topic, queue or any other processing entity.
+A _resource_ can be divided into many sub-parts known as _partitions_.
+
+
+##### Define the State Model and Constraints
+
+For scalability and fault tolerance, each partition can have one or more replicas.
+The __state model__ allows one to declare the system behavior by first enumerating the various STATES, and the TRANSITIONS between them.
+A simple model is ONLINE-OFFLINE where ONLINE means the task is active and OFFLINE means it\'s not active.
+You can also specify how many replicas must be in each state, these are known as __constraints__.
+For example, in a search system, one might need more than one node serving the same index to handle the load.
+
+The allowed states:
+
+* MASTER
+* SLAVE
+* OFFLINE
+
+The allowed transitions:
+
+* OFFLINE to SLAVE
+* SLAVE to OFFLINE
+* SLAVE to MASTER
+* MASTER to SLAVE
+
+The constraints:
+
+* no more than 1 MASTER per partition
+* the rest of the replicas should be slaves
+
+The following snippet shows how to declare the _state model_ and _constraints_ for the MASTER-SLAVE model.
+
+```
+StateModelDefinition.Builder builder = new StateModelDefinition.Builder(STATE_MODEL_NAME);
+
+// Add states and their rank to indicate priority. A lower rank corresponds to a higher priority
+builder.addState(MASTER, 1);
+builder.addState(SLAVE, 2);
+builder.addState(OFFLINE);
+
+// Set the initial state when the node starts
+builder.initialState(OFFLINE);
+
+// Add transitions between the states.
+builder.addTransition(OFFLINE, SLAVE);
+builder.addTransition(SLAVE, OFFLINE);
+builder.addTransition(SLAVE, MASTER);
+builder.addTransition(MASTER, SLAVE);
+
+// set constraints on states.
+
+// static constraint: upper bound of 1 MASTER
+builder.upperBound(MASTER, 1);
+
+// dynamic constraint: R means it should be derived based on the replication factor for the cluster
+// this allows a different replication factor for each resource without
+// having to define a new state model
+//
+builder.dynamicUpperBound(SLAVE, "R");
+StateModelDefinition statemodelDefinition = builder.build();
+```
+
+Then, add the state model definition:
+
+```
+clusterAccessor.addStateModelDefinitionToCluster(stateModelDefinition);
+```
+
+OR
+
+```
+admin.addStateModelDef(CLUSTER_NAME, STATE_MODEL_NAME, stateModelDefinition);
+```
+
+##### Assigning Partitions to Nodes
+
+The final goal of Helix is to ensure that the constraints on the state model are satisfied.
+Helix does this by assigning a __state__ to a partition (such as MASTER, SLAVE), and placing it on a particular node.
+
+There are 3 assignment modes Helix can operate on
+
+* FULL_AUTO: Helix decides the placement and state of a partition.
+* SEMI_AUTO: Application decides the placement but Helix decides the state of a partition.
+* CUSTOMIZED: Application controls the placement and state of a partition.
+
+For more info on the assignment modes, see [Rebalancing Algorithms](./tutorial_rebalance.html) section of the tutorial.
+
+Here is an example of adding the resource in SEMI_AUTO mode (i.e. locations of partitions are specified a priori):
+
+```
+int NUM_PARTITIONS = 6;
+int NUM_REPLICAS = 2;
+ResourceId resourceId = resourceId.from("MyDB");
+
+SemiAutoRebalancerContext context = new SemiAutoRebalancerContext.Builder(resourceId)
+  .replicaCount(NUM_REPLICAS).addPartitions(NUM_PARTITIONS)
+  .stateModelDefId(stateModelDefinition.getStateModelDefId())
+  .addPreferenceList(partition1Id, preferenceList) // preferred locations of each partition
+  // add other preference lists per partition
+  .build();
+
+// or add all preference lists at once if desired (map of PartitionId to List of ParticipantId)
+context.setPreferenceLists(preferenceLists);
+
+// or generate a default set of preference lists given the set of all participants
+context.generateDefaultConfiguration(stateModelDefinition, participantIdSet);
+
+// add the resource to the cluster
+ResourceConfig resourceConfig = new ResourceConfig.Builder(resourceId)
+  .rebalancerContext(context)
+  .build();
+clusterAccessor.addResourceToCluster(resourceConfig);
+```
+
+OR
+
+```
+String RESOURCE_NAME = "MyDB";
+int NUM_PARTITIONS = 6;
+String MODE = "SEMI_AUTO";
+int NUM_REPLICAS = 2;
+
+admin.addResource(CLUSTER_NAME, RESOURCE_NAME, NUM_PARTITIONS, STATE_MODEL_NAME, MODE);
+
+// specify the preference lists yourself
+IdealState idealState = admin.getResourceIdealState(CLUSTER_NAME, RESOURCE_NAME);
+idealState.setPreferenceList(partitionId, preferenceList); // preferred locations of each partition
+// add other preference lists per partition
+
+// or add all preference lists at once if desired
+idealState.getRecord().setListFields(preferenceLists);
+admin.setResourceIdealState(CLUSTER_NAME, RESOURCE_NAME, idealState);
+
+// or generate a default set of preference lists
+admin.rebalance(CLUSTER_NAME, RESOURCE_NAME, NUM_REPLICAS);
+```
+

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/index.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+<head>
+  <title>Helix 0.7.0-incubating Documentation [ALPHA]</title>
+</head>
+
+### Get Helix
+
+[Download](./download.html)
+
+[Building](./Building.html)
+
+[Release Notes](./releasenotes/release-0.7.0-incubating.html)
+
+### Hands-On
+
+[Quickstart](./Quickstart.html)
+
+[Tutorial](./Tutorial.html)
+
+[Javadocs](http://helix.incubator.apache.org/javadocs/0.7.0-incubating/index.html)
+
+### Recipes
+
+[Distributed lock manager](./recipes/lock_manager.html)
+
+[Rabbit MQ consumer group](./recipes/rabbitmq_consumer_group.html)
+
+[Rsync replicated file store](./recipes/rsync_replicated_file_store.html)
+
+[Service discovery](./recipes/service_discovery.html)
+
+[Distributed task DAG execution](./recipes/task_dag_execution.html)
+
+[User-Defined Rebalancer Example](./recipes/user_def_rebalancer.html)
+
+---
+
+### Alpha!
+This release contains many new features, but things might not work just right, and some APIs are still in the process of being developed.
+

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/recipes/lock_manager.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+Distributed Lock Manager
+------------------------
+Distributed locks are used to synchronize accesses shared resources. Most applications today use ZooKeeper to model distributed locks.
+
+The simplest way to model a lock using ZooKeeper is (See ZooKeeper leader recipe for an exact and more advanced solution)
+
+* Each process tries to create an emphemeral node
+* If the node is successfully created, the process acquires the lock
+* Otherwise, it will watch the ZNode and try to acquire the lock again if the current lock holder disappears
+
+This is good enough if there is only one lock. But in practice, an application will need many such locks. Distributing and managing the locks among difference process becomes challenging. Extending such a solution to many locks will result in:
+
+* Uneven distribution of locks among nodes; the node that starts first will acquire all the locks. Nodes that start later will be idle.
+* When a node fails, how the locks will be distributed among remaining nodes is not predicable.
+* When new nodes are added the current nodes don\'t relinquish the locks so that new nodes can acquire some locks
+
+In other words we want a system to satisfy the following requirements.
+
+* Distribute locks evenly among all nodes to get better hardware utilization
+* If a node fails, the locks that were acquired by that node should be evenly distributed among other nodes
+* If nodes are added, locks must be evenly re-distributed among nodes.
+
+Helix provides a simple and elegant solution to this problem. Simply specify the number of locks and Helix will ensure that above constraints are satisfied.
+
+To quickly see this working run the `lock-manager-demo` script where 12 locks are evenly distributed among three nodes, and when a node fails, the locks get re-distributed among remaining two nodes. Note that Helix does not re-shuffle the locks completely, instead it simply distributes the locks relinquished by dead node among 2 remaining nodes evenly.
+
+----------------------------------------------------------------------------------------
+
+### Short Version
+This version starts multiple threads within the same process to simulate a multi node deployment. Try the long version to get a better idea of how it works.
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout tags/helix-0.7.0-incubating
+mvn clean install package -DskipTests
+cd recipes/distributed-lock-manager/target/distributed-lock-manager-pkg/bin
+chmod +x *
+./lock-manager-demo
+```
+
+#### Output
+
+```
+./lock-manager-demo
+STARTING localhost_12000
+STARTING localhost_12002
+STARTING localhost_12001
+STARTED localhost_12000
+STARTED localhost_12002
+STARTED localhost_12001
+localhost_12001 acquired lock:lock-group_3
+localhost_12000 acquired lock:lock-group_8
+localhost_12001 acquired lock:lock-group_2
+localhost_12001 acquired lock:lock-group_4
+localhost_12002 acquired lock:lock-group_1
+localhost_12002 acquired lock:lock-group_10
+localhost_12000 acquired lock:lock-group_7
+localhost_12001 acquired lock:lock-group_5
+localhost_12002 acquired lock:lock-group_11
+localhost_12000 acquired lock:lock-group_6
+localhost_12002 acquired lock:lock-group_0
+localhost_12000 acquired lock:lock-group_9
+lockName    acquired By
+======================================
+lock-group_0    localhost_12002
+lock-group_1    localhost_12002
+lock-group_10    localhost_12002
+lock-group_11    localhost_12002
+lock-group_2    localhost_12001
+lock-group_3    localhost_12001
+lock-group_4    localhost_12001
+lock-group_5    localhost_12001
+lock-group_6    localhost_12000
+lock-group_7    localhost_12000
+lock-group_8    localhost_12000
+lock-group_9    localhost_12000
+Stopping localhost_12000
+localhost_12000 Interrupted
+localhost_12001 acquired lock:lock-group_9
+localhost_12001 acquired lock:lock-group_8
+localhost_12002 acquired lock:lock-group_6
+localhost_12002 acquired lock:lock-group_7
+lockName    acquired By
+======================================
+lock-group_0    localhost_12002
+lock-group_1    localhost_12002
+lock-group_10    localhost_12002
+lock-group_11    localhost_12002
+lock-group_2    localhost_12001
+lock-group_3    localhost_12001
+lock-group_4    localhost_12001
+lock-group_5    localhost_12001
+lock-group_6    localhost_12002
+lock-group_7    localhost_12002
+lock-group_8    localhost_12001
+lock-group_9    localhost_12001
+
+```
+
+----------------------------------------------------------------------------------------
+
+### Long version
+This provides more details on how to setup the cluster and where to plugin application code.
+
+#### Start ZooKeeper
+
+```
+./start-standalone-zookeeper 2199
+```
+
+#### Create a Cluster
+
+```
+./helix-admin --zkSvr localhost:2199 --addCluster lock-manager-demo
+```
+
+#### Create a Lock Group
+
+Create a lock group and specify the number of locks in the lock group.
+
+```
+./helix-admin --zkSvr localhost:2199  --addResource lock-manager-demo lock-group 6 OnlineOffline AUTO_REBALANCE
+```
+
+#### Start the Nodes
+
+Create a Lock class that handles the callbacks.
+
+```
+public class Lock extends StateModel {
+  private String lockName;
+
+  public Lock(String lockName) {
+    this.lockName = lockName;
+  }
+
+  public void lock(Message m, NotificationContext context) {
+    System.out.println(" acquired lock:"+ lockName );
+  }
+
+  public void release(Message m, NotificationContext context) {
+    System.out.println(" releasing lock:"+ lockName );
+  }
+
+}
+```
+
+and a LockFactory that creates Locks
+
+```
+public class LockFactory extends StateModelFactory<Lock> {
+    /* Instantiates the lock handler, one per lockName */
+    public Lock create(String lockName) {
+        return new Lock(lockName);
+    }
+}
+```
+
+At node start up, simply join the cluster and Helix will invoke the appropriate callbacks on the appropriate Lock instance. One can start any number of nodes and Helix detects that a new node has joined the cluster and re-distributes the locks automatically.
+
+```
+public class LockProcess {
+  public static void main(String args) {
+    String zkAddress= "localhost:2199";
+    String clusterName = "lock-manager-demo";
+    //Give a unique id to each process, most commonly used format hostname_port
+    String instanceName ="localhost_12000";
+    ZKHelixAdmin helixAdmin = new ZKHelixAdmin(zkAddress);
+    //configure the instance and provide some metadata
+    InstanceConfig config = new InstanceConfig(instanceName);
+    config.setHostName("localhost");
+    config.setPort("12000");
+    admin.addInstance(clusterName, config);
+    //join the cluster
+    HelixManager manager;
+    manager = HelixManagerFactory.getHelixManager(clusterName,
+                                                  instanceName,
+                                                  InstanceType.PARTICIPANT,
+                                                  zkAddress);
+    manager.getStateMachineEngine().registerStateModelFactory("OnlineOffline", modelFactory);
+    manager.connect();
+    Thread.currentThread.join();
+  }
+}
+```
+
+#### Start the Controller
+
+The controller can be started either as a separate process or can be embedded within each node process
+
+##### Separate Process
+This is recommended when number of nodes in the cluster \> 100. For fault tolerance, you can run multiple controllers on different boxes.
+
+```
+./run-helix-controller --zkSvr localhost:2199 --cluster lock-manager-demo 2>&1 > /tmp/controller.log &
+```
+
+##### Embedded Within the Node Process
+This is recommended when the number of nodes in the cluster is less than 100. To start a controller from each process, simply add the following lines to MyClass
+
+```
+public class LockProcess {
+  public static void main(String args) {
+    String zkAddress= "localhost:2199";
+    String clusterName = "lock-manager-demo";
+    // .
+    // .
+    manager.connect();
+    HelixManager controller;
+    controller = HelixControllerMain.startHelixController(zkAddress,
+                                                          clusterName,
+                                                          "controller",
+                                                          HelixControllerMain.STANDALONE);
+    Thread.currentThread.join();
+  }
+}
+```

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/recipes/rabbitmq_consumer_group.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+
+RabbitMQ Consumer Group
+-----------------------
+
+[RabbitMQ](http://www.rabbitmq.com/) is well-known open source software the provides robust messaging for applications.
+
+One of the commonly implemented recipes using this software is a work queue.  [http://www.rabbitmq.com/tutorials/tutorial-four-java.html](http://www.rabbitmq.com/tutorials/tutorial-four-java.html) describes the use case where
+
+* A producer sends a message with a routing key
+* The message is routed to the queue whose binding key exactly matches the routing key of the message
+* There are multiple consumers and each consumer is interested in processing only a subset of the messages by binding to the interested keys
+
+The example provided [here](http://www.rabbitmq.com/tutorials/tutorial-four-java.html) describes how multiple consumers can be started to process all the messages.
+
+While this works, in production systems one needs the following:
+
+* Ability to handle failures: when a consumer fails, another consumer must be started or the other consumers must start processing these messages that should have been processed by the failed consumer
+* When the existing consumers cannot keep up with the task generation rate, new consumers will be added. The tasks must be redistributed among all the consumers
+
+In this recipe, we demonstrate handling of consumer failures and new consumer additions using Helix.
+
+Mapping this usecase to Helix is pretty easy as the binding key/routing key is equivalent to a partition.
+
+Let's take an example. Lets say the queue has 6 partitions, and we have 2 consumers to process all the queues.
+What we want is all 6 queues to be evenly divided among 2 consumers.
+Eventually when the system scales, we add more consumers to keep up. This will make each consumer process tasks from 2 queues.
+Now let's say that a consumer failed, reducing the number of active consumers to 2. This means each consumer must process 3 queues.
+
+We showcase how such a dynamic application can be developed using Helix. Even though we use RabbitMQ as the pub/sub system one can extend this solution to other pub/sub systems.
+
+### Try It
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout tags/helix-0.7.0-incubating
+mvn clean install package -DskipTests
+cd recipes/rabbitmq-consumer-group/bin
+chmod +x *
+export HELIX_PKG_ROOT=`pwd`/helix-core/target/helix-core-pkg
+export HELIX_RABBITMQ_ROOT=`pwd`/recipes/rabbitmq-consumer-group/
+chmod +x $HELIX_PKG_ROOT/bin/*
+chmod +x $HELIX_RABBITMQ_ROOT/bin/*
+```
+
+#### Install RabbitMQ
+
+Setting up RabbitMQ on a local box is straightforward. You can find the instructions here
+http://www.rabbitmq.com/download.html
+
+#### Start ZK
+
+Start ZooKeeper at port 2199
+
+```
+$HELIX_PKG_ROOT/bin/start-standalone-zookeeper 2199
+```
+
+#### Setup the Consumer Group Cluster
+
+This will setup the cluster by creating a "rabbitmq-consumer-group" cluster and adds a "topic" with "6" queues.
+
+```
+$HELIX_RABBITMQ_ROOT/bin/setup-cluster.sh localhost:2199
+```
+
+#### Add Consumers
+
+Start 2 consumers in 2 different terminals. Each consumer is given a unique ID.
+
+```
+//start-consumer.sh zookeeperAddress (e.g. localhost:2181) consumerId , rabbitmqServer (e.g. localhost)
+$HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199 0 localhost
+$HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199 1 localhost
+
+```
+
+#### Start the Helix Controller
+
+Now start a Helix controller that starts managing the "rabbitmq-consumer-group" cluster.
+
+```
+$HELIX_RABBITMQ_ROOT/bin/start-cluster-manager.sh localhost:2199
+```
+
+#### Send Messages to the Topic
+
+Start sending messages to the topic. This script randomly selects a routing key (1-6) and sends the message to topic.
+Based on the key, messages gets routed to the appropriate queue.
+
+```
+$HELIX_RABBITMQ_ROOT/bin/send-message.sh localhost 20
+```
+
+After running this, you should see all 20 messages being processed by 2 consumers.
+
+#### Add Another Consumer
+
+Once a new consumer is started, Helix detects it. In order to balance the load between 3 consumers, it deallocates 1 partition from the existing consumers and allocates it to the new consumer. We see that
+each consumer is now processing only 2 queues.
+Helix makes sure that old nodes are asked to stop consuming before the new consumer is asked to start consuming for a given partition. But the transitions for each partition can happen in parallel.
+
+```
+$HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199 2 localhost
+```
+
+Send messages again to the topic
+
+```
+$HELIX_RABBITMQ_ROOT/bin/send-message.sh localhost 100
+```
+
+You should see that messages are now received by all 3 consumers.
+
+#### Stop a Consumer
+
+In any terminal press CTRL^C and notice that Helix detects the consumer failure and distributes the 2 partitions that were processed by failed consumer to the remaining 2 active consumers.
+
+
+### How does this work?
+
+Find the entire code [here](https://git-wip-us.apache.org/repos/asf?p=incubator-helix.git;a=tree;f=recipes/rabbitmq-consumer-group/src/main/java/org/apache/helix/recipes/rabbitmq).
+
+#### Cluster Setup
+
+This step creates ZNode on ZooKeeper for the cluster and adds the state model. We use online offline state model since there is no need for other states. The consumer is either processing a queue or it is not.
+
+It creates a resource called "rabbitmq-consumer-group" with 6 partitions. The execution mode is set to AUTO_REBALANCE. This means that the Helix controls the assignment of partition to consumers and automatically distributes the partitions evenly among the active consumers. When a consumer is added or removed, it ensures that a minimum number of partitions are shuffled.
+
+```
+zkclient = new ZkClient(zkAddr, ZkClient.DEFAULT_SESSION_TIMEOUT,
+    ZkClient.DEFAULT_CONNECTION_TIMEOUT, new ZNRecordSerializer());
+ZKHelixAdmin admin = new ZKHelixAdmin(zkclient);
+
+// add cluster
+admin.addCluster(clusterName, true);
+
+// add state model definition
+StateModelConfigGenerator generator = new StateModelConfigGenerator();
+admin.addStateModelDef(clusterName, "OnlineOffline",
+    new StateModelDefinition(generator.generateConfigForOnlineOffline()));
+
+// add resource "topic" which has 6 partitions
+String resourceName = "rabbitmq-consumer-group";
+admin.addResource(clusterName, resourceName, 6, "OnlineOffline", "AUTO_REBALANCE");
+```
+
+### Starting the Consumers
+
+The only thing consumers need to know is the ZooKeeper address, cluster name and consumer ID. It does not need to know anything else.
+
+```
+_manager = HelixManagerFactory.getZKHelixManager(_clusterName,
+                                                 _consumerId,
+                                                 InstanceType.PARTICIPANT,
+                                                 _zkAddr);
+
+StateMachineEngine stateMach = _manager.getStateMachineEngine();
+ConsumerStateModelFactory modelFactory =
+    new ConsumerStateModelFactory(_consumerId, _mqServer);
+stateMach.registerStateModelFactory("OnlineOffline", modelFactory);
+
+_manager.connect();
+```
+
+Once the consumer has registered the state model and the controller is started, the consumer starts getting callbacks (onBecomeOnlineFromOffline) for the partition it needs to host. All it needs to do as part of the callback is to start consuming messages from the appropriate queue. Similarly, when the controller deallocates a partitions from a consumer, it fires onBecomeOfflineFromOnline for the same partition.
+As a part of this transition, the consumer will stop consuming from a that queue.
+
+```
+@Transition(to = "ONLINE", from = "OFFLINE")
+public void onBecomeOnlineFromOffline(Message message, NotificationContext context) {
+  LOG.debug(_consumerId + " becomes ONLINE from OFFLINE for " + _partition);
+  if (_thread == null) {
+    LOG.debug("Starting ConsumerThread for " + _partition + "...");
+    _thread = new ConsumerThread(_partition, _mqServer, _consumerId);
+    _thread.start();
+    LOG.debug("Starting ConsumerThread for " + _partition + " done");
+
+  }
+}
+
+@Transition(to = "OFFLINE", from = "ONLINE")
+public void onBecomeOfflineFromOnline(Message message, NotificationContext context)
+    throws InterruptedException {
+  LOG.debug(_consumerId + " becomes OFFLINE from ONLINE for " + _partition);
+  if (_thread != null) {
+    LOG.debug("Stopping " + _consumerId + " for " + _partition + "...");
+    _thread.interrupt();
+    _thread.join(2000);
+    _thread = null;
+    LOG.debug("Stopping " +  _consumerId + " for " + _partition + " done");
+  }
+}
+```

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/recipes/rsync_replicated_file_store.md
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diff --git a/website/0.7.0-incubating/src/site/markdown/recipes/rsync_replicated_file_store.md b/website/0.7.0-incubating/src/site/markdown/recipes/rsync_replicated_file_store.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+Near-Realtime Rsync Replicated File System
+------------------------------------------
+
+### Quick Demo
+
+* This demo starts 3 instances with id's as ```localhost_12001, localhost_12002, localhost_12003```
+* Each instance stores its files under ```/tmp/<id>/filestore```
+* ```localhost_12001``` is designated as the master, and ```localhost_12002``` and ```localhost_12003``` are the slaves
+* Files written to the master are replicated to the slaves automatically. In this demo, a.txt and b.txt are written to ```/tmp/localhost_12001/filestore``` and they get replicated to other folders.
+* When the master is stopped, ```localhost_12002``` is promoted to master.
+* The other slave ```localhost_12003``` stops replicating from ```localhost_12001``` and starts replicating from new master ```localhost_12002```
+* Files written to new master ```localhost_12002``` are replicated to ```localhost_12003```
+* In the end state of this quick demo, ```localhost_12002``` is the master and ```localhost_12003``` is the slave. Manually create files under ```/tmp/localhost_12002/filestore``` and see that appear in ```/tmp/localhost_12003/filestore```
+* Ignore the interrupted exceptions on the console :-)
+
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout tags/helix-0.7.0-incubating
+cd recipes/rsync-replicated-file-system/
+mvn clean install package -DskipTests
+cd target/rsync-replicated-file-system-pkg/bin
+chmod +x *
+./quickdemo
+
+```
+
+### Overview
+
+There are many applications that require storage for storing large number of relatively small data files. Examples include media stores to store small videos, images, mail attachments etc. Each of these objects is typically kilobytes, often no larger than a few megabytes. An additional distinguishing feature of these use cases is that files are typically only added or deleted, rarely updated. When there are updates, they do not have any concurrency requirements.
+
+These are much simpler requirements than what general purpose distributed file system have to satisfy; these would include concurrent access to files, random access for reads and updates, posix compliance, and others. To satisfy those requirements, general DFSs are also pretty complex that are expensive to build and maintain.
+
+A different implementation of a distributed file system includes HDFS which is inspired by Google's GFS. This is one of the most widely used distributed file system that forms the main data storage platform for Hadoop. HDFS is primary aimed at processing very large data sets and distributes files across a cluster of commodity servers by splitting up files in fixed size chunks. HDFS is not particularly well suited for storing a very large number of relatively tiny files.
+
+### File Store
+
+It's possible to build a vastly simpler system for the class of applications that have simpler requirements as we have pointed out.
+
+* Large number of files but each file is relatively small
+* Access is limited to create, delete and get entire files
+* No updates to files that are already created (or it's feasible to delete the old file and create a new one)
+
+
+We call this system a Partitioned File Store (PFS) to distinguish it from other distributed file systems. This system needs to provide the following features:
+
+* CRD access to large number of small files
+* Scalability: Files should be distributed across a large number of commodity servers based on the storage requirement
+* Fault-tolerance: Each file should be replicated on multiple servers so that individual server failures do not reduce availability
+* Elasticity: It should be possible to add capacity to the cluster easily
+
+
+Apache Helix is a generic cluster management framework that makes it very easy to provide scalability, fault-tolerance and elasticity features.
+rsync can be easily used as a replication channel between servers so that each file gets replicated on multiple servers.
+
+### Design
+
+#### High Level
+
+* Partition the file system based on the file name
+* At any time a single writer can write, we call this a master
+* For redundancy, we need to have additional replicas called slave. Slaves can optionally serve reads
+* Slave replicates data from the master
+* When a master fails, a slave gets promoted to master
+
+#### Transaction Log
+
+Every write on the master will result in creation/deletion of one or more files. In order to maintain timeline consistency slaves need to apply the changes in the same order
+To facilitate this, the master logs each transaction in a file and each transaction is associated with an 64 bit ID in which the 32 LSB represents a sequence number and MSB represents the generation number
+The sequence number gets incremented on every transaction and the generation is incremented when a new master is elected
+
+#### Replication
+
+Replication is required for slaves to keep up with changes on the master. Every time the slave applies a change it checkpoints the last applied transaction ID.
+During restarts, this allows the slave to pull changes from the last checkpointed ID. Similar to master, the slave logs each transaction to the transaction logs but instead of generating new transaction ID, it uses the same ID generated by the master.
+
+
+#### Failover
+
+When a master fails, a new slave will be promoted to master. If the previous master node is reachable, then the new master will flush all the
+changes from previous the master before taking up mastership. The new master will record the end transaction ID of the current generation and then start a new generation
+with sequence starting from 1. After this the master will begin accepting writes.
+
+![Partitioned File Store](../images/PFS-Generic.png)
+
+
+
+### Rsync-based Solution
+
+![Rsync based File Store](../images/RSYNC_BASED_PFS.png)
+
+
+This application demonstrates a file store that uses rsync as the replication mechanism. One can envision a similar system where instead of using rsync, one
+can implement a custom solution to notify the slave of the changes and also provide an api to pull the change files.
+
+#### Concepts
+* file_store_dir: Root directory for the actual data files
+* change_log_dir: The transaction logs are generated under this folder
+* check_point_dir: The slave stores the check points ( last processed transaction) here
+
+#### Master
+* File server: This component supports file uploads and downloads and writes the files to ```file_store_dir```. This is not included in this application. The idea is that most applications have different ways of implementing this component and have some associated business logic. It is not hard to come up with such a component if needed.
+* File store watcher: This component watches the ```file_store_dir``` directory on the local file system for any changes and notifies the registered listeners of the changes
+* Change log generator: This registers as a listener of the file store watcher and on each notification logs the changes into a file under ```change_log_dir```
+
+#### Slave
+* File server: This component on the slave will only support reads
+* Cluster state observer: Slave observes the cluster state and is able to know who is the current master
+* Replicator: This has two subcomponents
+    - Periodic rsync of change log: This is a background process that periodically rsyncs the ```change_log_dir``` of the master to its local directory
+    - Change Log Watcher: This watches the ```change_log_dir``` for changes and notifies the registered listeners of the change
+    - On demand rsync invoker: This is registered as a listener to change log watcher and on every change invokes rsync to sync only the changed file
+
+#### Coordination
+
+The coordination between nodes is done by Helix. Helix does the partition management and assigns the partition to multiple nodes based on the replication factor. It elects one the nodes as master and designates others as slaves.
+It provides notifications to each node in the form of state transitions (Offline to Slave, Slave to Master). It also provides notifications when there is change is cluster state.
+This allows the slave to stop replicating from current master and start replicating from new master.
+
+In this application, we have only one partition but its very easy to extend it to support multiple partitions. By partitioning the file store, one can add new nodes and Helix will automatically
+re-distribute partitions among the nodes. To summarize, Helix provides partition management, fault tolerance and facilitates automated cluster expansion.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/recipes/service_discovery.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+Service Discovery
+-----------------
+
+One of the common usage of ZooKeeper is to enable service discovery.
+The basic idea is that when a server starts up it advertises its configuration/metadata such as its hostname and port on ZooKeeper.
+This allows clients to dynamically discover the servers that are currently active. One can think of this like a service registry to which a server registers when it starts and
+is automatically deregistered when it shutdowns or crashes. In many cases it serves as an alternative to VIPs.
+
+The core idea behind this is to use ZooKeeper ephemeral nodes. The ephemeral nodes are created when the server registers and all its metadata is put into a ZNode.
+When the server shutdowns, ZooKeeper automatically removes this ZNode.
+
+There are two ways the clients can dynamically discover the active servers:
+
+### ZooKeeper Watch
+
+Clients can set a child watch under specific path on ZooKeeper.
+When a new service is registered/deregistered, ZooKeeper notifies the client via a watch event and the client can read the list of services. Even though this looks trivial,
+there are lot of things one needs to keep in mind like ensuring that you first set the watch back on ZooKeeper before reading data.
+
+
+### Poll
+
+Another approach is for the client to periodically read the ZooKeeper path and get the list of services.
+
+Both approaches have pros and cons, for example setting a watch might trigger herd effect if there are large number of clients. This is problematic, especially when servers are starting up.
+But the advantage to setting watches is that clients are immediately notified of a change which is not true in case of polling.
+In some cases, having both watches and polls makes sense; watch allows one to get notifications as soon as possible while poll provides a safety net if a watch event is missed because of code bug or ZooKeeper fails to notify.
+
+### Other Developer Considerations
+* What happens when the ZooKeeper session expires? All the watches and ephemeral nodes previously added or created by this server are lost. One needs to add the watches again, recreate the ephemeral nodes, and so on.
+* Due to network issues or Java GC pauses session expiry might happen again and again; this phenomenon is known as flapping. It\'s important for the server to detect this and deregister itself.
+
+### Other Operational Considerations
+* What if the node is behaving badly? One might kill the server, but it will lose the ability to debug. It would be nice to have the ability to mark a server as disabled and clients know that a node is disabled and will not contact that node.
+
+### Configuration Ownership
+
+This is an important aspect that is often ignored in the initial stages of your development. Typically, the service discovery pattern means that servers start up with some configuration which it simply puts into ZooKeeper. While this works well in the beginning, configuration management becomes very difficult since the servers themselves are statically configured. Any change in server configuration implies restarting the server. Ideally, it will be nice to have the ability to change configuration dynamically without having to restart a server.
+
+Ideally you want a hybrid solution, a node starts with minimal configuration and gets the rest of configuration from ZooKeeper.
+
+### Using Helix for Service Discovery
+
+Even though Helix has a higher-level abstraction in terms of state machines, constraints and objectives, service discovery is one of things has been a prevalent use case from the start.
+The controller uses the exact mechanism we described above to discover when new servers join the cluster. We create these ZNodes under /CLUSTERNAME/LIVEINSTANCES.
+Since at any time there is only one controller, we use a ZK watch to track the liveness of a server.
+
+This recipe simply demonstrates how one can re-use that part for implementing service discovery. This demonstrates multiple modes of service discovery:
+
+* POLL: The client reads from zookeeper at regular intervals 30 seconds. Use this if you have 100's of clients
+* WATCH: The client sets up watcher and gets notified of the changes. Use this if you have 10's of clients
+* NONE: This does neither of the above, but reads directly from zookeeper when ever needed
+
+Helix provides these additional features compared to other implementations available elsewhere:
+
+* It has the concept of disabling a node which means that a badly behaving node can be disabled using the Helix admin API
+* It automatically detects if a node connects/disconnects from zookeeper repeatedly and disables the node
+* Configuration management
+    * Allows one to set configuration via the admin API at various granulaties like cluster, instance, resource, partition
+    * Configurations can be dynamically changed
+    * The server is notified when configurations change
+
+
+### Checkout and Build
+
+```
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout tags/helix-0.7.0-incubating
+mvn clean install package -DskipTests
+cd recipes/service-discovery/target/service-discovery-pkg/bin
+chmod +x *
+```
+
+### Start ZooKeeper
+
+```
+./start-standalone-zookeeper 2199
+```
+
+### Run the Demo
+
+```
+./service-discovery-demo.sh
+```
+
+### Output
+
+```
+START:Service discovery demo mode:WATCH
+	Registering service
+		host.x.y.z_12000
+		host.x.y.z_12001
+		host.x.y.z_12002
+		host.x.y.z_12003
+		host.x.y.z_12004
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12000
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12002
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Deregistering service:
+		host.x.y.z_12002
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12000
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Registering service:host.x.y.z_12002
+END:Service discovery demo mode:WATCH
+=============================================
+START:Service discovery demo mode:POLL
+	Registering service
+		host.x.y.z_12000
+		host.x.y.z_12001
+		host.x.y.z_12002
+		host.x.y.z_12003
+		host.x.y.z_12004
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12000
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12002
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Deregistering service:
+		host.x.y.z_12002
+	Sleeping for poll interval:30000
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12000
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Registering service:host.x.y.z_12002
+END:Service discovery demo mode:POLL
+=============================================
+START:Service discovery demo mode:NONE
+	Registering service
+		host.x.y.z_12000
+		host.x.y.z_12001
+		host.x.y.z_12002
+		host.x.y.z_12003
+		host.x.y.z_12004
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12000
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12002
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Deregistering service:
+		host.x.y.z_12000
+	SERVICES AVAILABLE
+		SERVICENAME 	HOST 			PORT
+		myServiceName 	host.x.y.z 		12001
+		myServiceName 	host.x.y.z 		12002
+		myServiceName 	host.x.y.z 		12003
+		myServiceName 	host.x.y.z 		12004
+	Registering service:host.x.y.z_12000
+END:Service discovery demo mode:NONE
+=============================================
+```

http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/bea21020/website/0.7.0-incubating/src/site/markdown/recipes/task_dag_execution.md
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+<!---
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+Distributed Task Execution
+--------------------------
+
+This recipe is intended to demonstrate how task dependencies can be modeled using primitives provided by Helix. A given task can be run with the desired amount of parallelism and will start only when upstream dependencies are met. The demo executes the task DAG described below using 10 workers. Although the demo starts the workers as threads, there is no requirement that all the workers need to run in the same process. In reality, these workers run on many different boxes on a cluster.  When worker fails, Helix takes care of re-assigning a failed task partition to a new worker.
+
+Redis is used as a result store. Any other suitable implementation for TaskResultStore can be plugged in.
+
+### Workflow
+
+#### Input
+
+10000 impression events and around 100 click events are pre-populated in task result store (redis).
+
+* **ImpEvent**: format: id,isFraudulent,country,gender
+
+* **ClickEvent**: format: id,isFraudulent,impEventId
+
+#### Stages
+
++ **FilterImps**: Filters impression where isFraudulent=true.
+
++ **FilterClicks**: Filters clicks where isFraudulent=true
+
++ **impCountsByGender**: Generates impression counts grouped by gender. It does this by incrementing the count for 'impression_gender_counts:<gender_value>' in the task result store (redis hash). Depends on: **FilterImps**
+
++ **impCountsByCountry**: Generates impression counts grouped by country. It does this by incrementing the count for 'impression_country_counts:<country_value>' in the task result store (redis hash). Depends on: **FilterClicks**
+
++ **impClickJoin**: Joins clicks with corresponding impression event using impEventId as the join key. Join is needed to pull dimensions not present in click event. Depends on: **FilterImps, FilterClicks**
+
++ **clickCountsByGender**: Generates click counts grouped by gender. It does this by incrementing the count for click_gender_counts:<gender_value> in the task result store (redis hash). Depends on: **impClickJoin**
+
++ **clickCountsByGender**: Generates click counts grouped by country. It does this by incrementing the count for click_country_counts:<country_value> in the task result store (redis hash). Depends on: **impClickJoin**
+
++ **report**: Reads from all aggregates generated by previous stages and prints them. Depends on: **impCountsByGender, impCountsByCountry, clickCountsByGender,clickCountsByGender**
+
+
+### Creating a DAG
+
+Each stage is represented as a Node along with the upstream dependency and desired parallelism.  Each stage is modeled as a resource in Helix using OnlineOffline state model. As part of an Offline to Online transition, we watch the external view of upstream resources and wait for them to transition to the online state. See Task.java for additional info.
+
+```
+Dag dag = new Dag();
+dag.addNode(new Node("filterImps", 10, ""));
+dag.addNode(new Node("filterClicks", 5, ""));
+dag.addNode(new Node("impClickJoin", 10, "filterImps,filterClicks"));
+dag.addNode(new Node("impCountsByGender", 10, "filterImps"));
+dag.addNode(new Node("impCountsByCountry", 10, "filterImps"));
+dag.addNode(new Node("clickCountsByGender", 5, "impClickJoin"));
+dag.addNode(new Node("clickCountsByCountry", 5, "impClickJoin"));
+dag.addNode(new Node("report",1,"impCountsByGender,impCountsByCountry,clickCountsByGender,clickCountsByCountry"));
+```
+
+### Demo
+
+In order to run the demo, use the following steps
+
+See http://redis.io/topics/quickstart on how to install redis server
+
+```
+Start redis e.g:
+./redis-server --port 6379
+
+git clone https://git-wip-us.apache.org/repos/asf/incubator-helix.git
+cd incubator-helix
+git checkout helix-0.7.0-incubating
+cd recipes/task-execution
+mvn clean install package -DskipTests
+cd target/task-execution-pkg/bin
+chmod +x task-execution-demo.sh
+./task-execution-demo.sh 2181 localhost 6379
+
+```
+
+Here\'s a visual representation of the DAG.
+
+```
+
+
+
+
+
+                       +-----------------+       +----------------+
+                       |   filterImps    |       |  filterClicks  |
+                       | (parallelism=10)|       | (parallelism=5)|
+                       +----------+-----++       +-------+--------+
+                       |          |     |                |
+                       |          |     |                |
+                       |          |     |                |
+                       |          |     +------->--------v------------+
+      +--------------<-+   +------v-------+    |  impClickJoin        |
+      |impCountsByGender   |impCountsByCountry | (parallelism=10)     |
+      |(parallelism=10)    |(parallelism=10)   ++-------------------+-+
+      +-----------+--+     +---+----------+     |                   |
+                  |            |                |                   |
+                  |            |                |                   |
+                  |            |       +--------v---------+       +-v-------------------+
+                  |            |       |clickCountsByGender       |clickCountsByCountry |
+                  |            |       |(parallelism=5)   |       |(parallelism=5)      |
+                  |            |       +----+-------------+       +---------------------+
+                  |            |            |                     |
+                  |            |            |                     |
+                  |            |            |                     |
+                  +----->+-----+>-----------v----+<---------------+
+                         | report                |
+                         |(parallelism=1)        |
+                         +-----------------------+
+
+```
+
+(credit for above ascii art: http://www.asciiflow.com)
+
+#### Output
+
+```
+Done populating dummy data
+Executing filter task for filterImps_3 for impressions_demo
+Executing filter task for filterImps_2 for impressions_demo
+Executing filter task for filterImps_0 for impressions_demo
+Executing filter task for filterImps_1 for impressions_demo
+Executing filter task for filterImps_4 for impressions_demo
+Executing filter task for filterClicks_3 for clicks_demo
+Executing filter task for filterClicks_1 for clicks_demo
+Executing filter task for filterImps_8 for impressions_demo
+Executing filter task for filterImps_6 for impressions_demo
+Executing filter task for filterClicks_2 for clicks_demo
+Executing filter task for filterClicks_0 for clicks_demo
+Executing filter task for filterImps_7 for impressions_demo
+Executing filter task for filterImps_5 for impressions_demo
+Executing filter task for filterClicks_4 for clicks_demo
+Executing filter task for filterImps_9 for impressions_demo
+Running AggTask for impCountsByGender_3 for filtered_impressions_demo gender
+Running AggTask for impCountsByGender_2 for filtered_impressions_demo gender
+Running AggTask for impCountsByGender_0 for filtered_impressions_demo gender
+Running AggTask for impCountsByGender_9 for filtered_impressions_demo gender
+Running AggTask for impCountsByGender_1 for filtered_impressions_demo gender
+Running AggTask for impCountsByGender_4 for filtered_impressions_demo gender
+Running AggTask for impCountsByCountry_4 for filtered_impressions_demo country
+Running AggTask for impCountsByGender_5 for filtered_impressions_demo gender
+Executing JoinTask for impClickJoin_2
+Running AggTask for impCountsByCountry_3 for filtered_impressions_demo country
+Running AggTask for impCountsByCountry_1 for filtered_impressions_demo country
+Running AggTask for impCountsByCountry_0 for filtered_impressions_demo country
+Running AggTask for impCountsByCountry_2 for filtered_impressions_demo country
+Running AggTask for impCountsByGender_6 for filtered_impressions_demo gender
+Executing JoinTask for impClickJoin_1
+Executing JoinTask for impClickJoin_0
+Executing JoinTask for impClickJoin_3
+Running AggTask for impCountsByGender_8 for filtered_impressions_demo gender
+Executing JoinTask for impClickJoin_4
+Running AggTask for impCountsByGender_7 for filtered_impressions_demo gender
+Running AggTask for impCountsByCountry_5 for filtered_impressions_demo country
+Running AggTask for impCountsByCountry_6 for filtered_impressions_demo country
+Executing JoinTask for impClickJoin_9
+Running AggTask for impCountsByCountry_8 for filtered_impressions_demo country
+Running AggTask for impCountsByCountry_7 for filtered_impressions_demo country
+Executing JoinTask for impClickJoin_5
+Executing JoinTask for impClickJoin_6
+Running AggTask for impCountsByCountry_9 for filtered_impressions_demo country
+Executing JoinTask for impClickJoin_8
+Executing JoinTask for impClickJoin_7
+Running AggTask for clickCountsByCountry_1 for joined_clicks_demo country
+Running AggTask for clickCountsByCountry_0 for joined_clicks_demo country
+Running AggTask for clickCountsByCountry_2 for joined_clicks_demo country
+Running AggTask for clickCountsByCountry_3 for joined_clicks_demo country
+Running AggTask for clickCountsByGender_1 for joined_clicks_demo gender
+Running AggTask for clickCountsByCountry_4 for joined_clicks_demo country
+Running AggTask for clickCountsByGender_3 for joined_clicks_demo gender
+Running AggTask for clickCountsByGender_2 for joined_clicks_demo gender
+Running AggTask for clickCountsByGender_4 for joined_clicks_demo gender
+Running AggTask for clickCountsByGender_0 for joined_clicks_demo gender
+Running reports task
+Impression counts per country
+{CANADA=1940, US=1958, CHINA=2014, UNKNOWN=2022, UK=1946}
+Click counts per country
+{US=24, CANADA=14, CHINA=26, UNKNOWN=14, UK=22}
+Impression counts per gender
+{F=3325, UNKNOWN=3259, M=3296}
+Click counts per gender
+{F=33, UNKNOWN=32, M=35}
+```


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