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Subject [GitHub] [zookeeper] hanm commented on a change in pull request #1073: ZOOKEEPER-3529: add a new doc: zookeeperUseCases.md
Date Fri, 13 Sep 2019 20:37:07 GMT
hanm commented on a change in pull request #1073: ZOOKEEPER-3529: add a new doc: zookeeperUseCases.md
URL: https://github.com/apache/zookeeper/pull/1073#discussion_r324349832
 
 

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+<!--
+Copyright 2002-2019 The Apache Software Foundation
+
+Licensed 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.
+//-->
+
+# ZooKeeper Use Cases
+
+- Applications and organizations using ZooKeeper include (alphabetically)[1].
+- If your use case wants to be listed here. Please do not hesitate, submit a pull request
or write an email to **dev@zookeeper.apache.org**,
+  and then, your use case will be included.
+
+
+## Free Software Projects
+
+### [AdroitLogic UltraESB](http://adroitlogic.org/)
+  - Uses ZooKeeper to implement node coordination, in clustering support. This allows the
management of the complete cluster,
+  or any specific node - from any other node connected via JMX. A Cluster wide command framework
developed on top of the
+  ZooKeeper coordination allows commands that fail on some nodes to be retried etc. We also
support the automated graceful
+  round-robin-restart of a complete cluster of nodes using the same framework.
+
+### [Akka](http://akka.io/)
+  - Akka is the platform for the next generation event-driven, scalable and fault-tolerant
architectures on the JVM.
+  Or: Akka is a toolkit and runtime for building highly concurrent, distributed, and fault
tolerant event-driven applications on the JVM.
+
+### [Eclipse Communication Framework](http://www.eclipse.org/ecf) 
+  - The Eclipse ECF project provides an implementation of its Abstract Discovery services
using Zookeeper. ECF itself
+  is used in many projects providing base functionallity for communication, all based on
OSGi.
+
+### [Eclipse Gyrex](http://www.eclipse.org/gyrex)
+  - The Eclipse Gyrex project provides a platform for building your own Java OSGi based clouds.

+  - ZooKeeper is used as the core cloud component for node membership and management, coordination
of jobs executing among workers,
+  a lock service and a simple queue service and a lot more.
+
+### [GoldenOrb](http://www.goldenorbos.org/)
+  - massive-scale Graph analysis
+
+### [Juju](https://juju.ubuntu.com/)
+  - Service deployment and orchestration framework, formerly called Ensemble.
+
+### [Katta](http://katta.sourceforge.net/)
+  - Katta serves distributed Lucene indexes in a grid environment.
+  - Zookeeper is used for node, master and index management in the grid.
+
+### [KeptCollections](https://github.com/anthonyu/KeptCollections)
+  - KeptCollections is a library of drop-in replacements for the data structures in the Java
Collections framework.
+  - KeptCollections uses Apache ZooKeeper as a backing store, thus making its data structures
distributed and scalable.
+
+### [Neo4j](https://neo4j.com/)
+  - Neo4j is a Graph Database. It's a disk based, ACID compliant transactional storage engine
for big graphs and fast graph traversals,
+    using external indicies like Lucene/Solr for global searches.
+  - We use ZooKeeper in the Neo4j High Availability components for write-master election,
+    read slave coordination and other cool stuff. ZooKeeper is a great and focused project
- we like!
+
+### [Norbert](http://sna-projects.com/norbert)
+  - Partitioned routing and cluster management.
+
+### [OpenStack Nova](http://www.openstack.org/)
+  - OpenStack  is an open source software stack for the creation and management of private
and public clouds. It is designed to manage pools of compute,
+    storage, and networking resources in data centers, allowing the management of these resources
through a consolidated dashboard and flexible APIs.
+  - Nova is the software component in OpenStack, which is responsible for managing the compute
resources, where virtual machines (VMs) are hosted in a cloud computing environment. It is
also known as the OpenStack Compute Service. OpenStack
+    Nova provides a cloud computing fabric controller, supporting a wide variety of virtualization
technologies such as KVM, Xen, VMware, and many more. In addition to its native API, it also
includes compatibility with Amazon EC2 and S3 APIs.
+    Nova depends on up-to-date information about the availability of the various compute
nodes and services that run on them, for its proper operation. For example, the virtual machine
placement operation requires to know the currently available compute nodes and their current
state.
+    Nova uses ZooKeeper to implement an efficient membership service, which monitors the
availability of registered services. This is done through the ZooKeeper ServiceGroup Driver,
which works by using ZooKeeper's ephemeral znodes. Each service registers by creating an ephemeral
znode on startup. Now, when the service dies, ZooKeeper will automatically delete the corresponding
ephemeral znode. The removal of this znode can be used to trigger the corresponding recovery
logic.
+    For example, when a compute node crashes, the nova-compute service that is running in
that node also dies. This causes the session with ZooKeeper service to expire, and as a result,
ZooKeeper deletes the ephemeral znode created by the nova-compute service. If the cloud controller
keeps a watch on this node-deletion event, it will come to know about the compute node crash
and can trigger a migration procedure to evacuate all the VMs that are running in the failed
compute node to other nodes. This way, high availability of the VMs can be ensured in real
time.
+  - ZooKeeper is also being considered for the following use cases in OpenStack Nova:
+    - Storing the configuration metadata (nova.conf)
+    - Maintaining high availability of services and automatic failover using
+    leader election
+
+### [spring-cloud-zookeeper](https://spring.io/projects/spring-cloud-zookeeper)
+  - Spring Cloud Zookeeper provides Apache Zookeeper integrations for Spring Boot apps through
autoconfiguration
+    and binding to the Spring Environment and other Spring programming model idioms. With
a few simple annotations
+    you can quickly enable and configure the common patterns inside your application and
build large distributed systems with Zookeeper.
+    The patterns provided include Service Discovery and Distributed Configuration.
+
+### [Talend ESB](http://www.talend.com/products-application-integration/application-integration-esb-se.php)
+  - Talend ESB is a versatile and flexible, enterprise service bus.
+  - It uses ZooKeeper as endpoint repository of both REST and SOAP Web services.
+    By using ZooKeeper Talend ESB is able to provide failover and load balancing capabilities
in a very light-weight manner
+
+### [redis_failover](https://github.com/ryanlecompte/redis_failover)
+  - Redis Failover is a ZooKeeper-based automatic master/slave failover solution for Ruby.
+
+
+## Apache Projects
+
+### [Apache Accumulo](https://accumulo.apache.org/)
+  - Accumulo is a distributed key/value store that provides expressive, cell-level access
labels.
+  - Apache ZooKeeper plays a central role within the Accumulo architecture. Its quorum consistency
model supports an overall
+    Accumulo architecture with no single points of failure. Beyond that, Accumulo leverages
ZooKeeper to store and communication 
+    configuration information for users and tables, as well as operational states of processes
and tablets.[2]
+
+### [Apache BookKeeper](https://bookkeeper.apache.org/)
+  - A scalable, fault-tolerant, and low-latency storage service optimized for real-time workloads.
+  - BookKeeper requires a metadata storage service to store information related to ledgers
and available bookies. BookKeeper currently uses
+    ZooKeeper for this and other tasks[3].
+
+### [Apache CXF DOSGi](http://cxf.apache.org/distributed-osgi.html)
+  - Apache CXF is an open source services framework. CXF helps you build and develop services
using frontend programming
+    APIs, like JAX-WS and JAX-RS. These services can speak a variety of protocols such as
SOAP, XML/HTTP, RESTful HTTP,
+    or CORBA and work over a variety of transports such as HTTP, JMS or JBI.
+  - The Distributed OSGi implementation at Apache CXF uses ZooKeeper for its Discovery functionality.[4]
+
+### [Apache Dubbo](http://dubbo.apache.org)
+  - Apache Dubbo is a high-performance, java based open source RPC framework.
+  - Zookeeper is used for service registration discovery and configuration management in
Dubbo.[6]
+
+### [Apache Flink](https://flink.apache.org/)
+  - Apache Flink is a framework and distributed processing engine for stateful computations
over unbounded and bounded data streams.
+    Flink has been designed to run in all common cluster environments, perform computations
at in-memory speed and at any scale.
+  - To enable JobManager High Availability you have to set the high-availability mode to
zookeeper, configure a ZooKeeper quorum and set up a masters file with all JobManagers hosts
and their web UI ports.
+    Flink leverages ZooKeeper for distributed coordination between all running JobManager
instances. ZooKeeper is a separate service from Flink,
+    which provides highly reliable distributed coordination via leader election and light-weight
consistent state storage[23].
+
+### [Apache Flume](https://flume.apache.org/)
+  - Flume is a distributed, reliable, and available service for efficiently collecting, aggregating,
and moving large amounts
+    of log data. It has a simple and flexible architecture based on streaming data flows.
It is robust and fault tolerant
+    with tunable reliability mechanisms and many failover and recovery mechanisms. It uses
a simple extensible data model
+    that allows for online analytic application.
+  - Flume supports Agent configurations via Zookeeper. This is an experimental feature.[5]
+
+### [Apache Hadoop](http://hadoop.apache.org/)
+  - The Apache Hadoop software library is a framework that allows for the distributed processing
of large data sets across
+    clusters of computers using simple programming models. It is designed to scale up from
single servers to thousands of machines,
+    each offering local computation and storage. Rather than rely on hardware to deliver
high-availability,
+    the library itself is designed to detect and handle failures at the application layer,
so delivering a highly-available service on top of a cluster of computers, each of which may
be prone to failures.
+  - The implementation of automatic HDFS failover relies on ZooKeeper for the following things:
+    - **Failure detection** - each of the NameNode machines in the cluster maintains a persistent
session in ZooKeeper.
+      If the machine crashes, the ZooKeeper session will expire, notifying the other NameNode
that a failover should be triggered.
+    - **Active NameNode election** - ZooKeeper provides a simple mechanism to exclusively
elect a node as active. If the current active NameNode crashes,
+      another node may take a special exclusive lock in ZooKeeper indicating that it should
become the next active.
+  - The ZKFailoverController (ZKFC) is a new component which is a ZooKeeper client which
also monitors and manages the state of the NameNode.
+    Each of the machines which runs a NameNode also runs a ZKFC, and that ZKFC is responsible
for:
+    - **Health monitoring** - the ZKFC pings its local NameNode on a periodic basis with
a health-check command.
+      So long as the NameNode responds in a timely fashion with a healthy status, the ZKFC
considers the node healthy.
+      If the node has crashed, frozen, or otherwise entered an unhealthy state, the health
monitor will mark it as unhealthy.
+    - **ZooKeeper session management** - when the local NameNode is healthy, the ZKFC holds
a session open in ZooKeeper.
+      If the local NameNode is active, it also holds a special “lock” znode. This lock
uses ZooKeeper’s support for “ephemeral” nodes;
+      if the session expires, the lock node will be automatically deleted.
+    - **ZooKeeper-based election** - if the local NameNode is healthy, and the ZKFC sees
that no other node currently holds the lock znode,
+      it will itself try to acquire the lock. If it succeeds, then it has “won the election”,
and is responsible for running a failover to make its local NameNode active.
+      The failover process is similar to the manual failover described above: first, the
previous active is fenced if necessary,
+      and then the local NameNode transitions to active state.[7]
+
+### [Apache HBase](https://hbase.apache.org/)
+  - HBase is the Hadoop database. It's an open-source, distributed, column-oriented store
model.
+  - HBase uses ZooKeeper for master election, server lease management, bootstrapping, and
coordination between servers.
+    A distributed Apache HBase installation depends on a running ZooKeeper cluster. All participating
nodes and clients
+    need to be able to access the running ZooKeeper ensemble.[8]
+  - As you can see, ZooKeeper is a fundamental part of HBase. All operations that require
coordination, such as Regions
+    assignment, Master-Failover, replication, and snapshots, are built on ZooKeeper[20].

+
+### [Apache Hedwig](https://bookkeeper.apache.org/docs/r4.2.3/hedwigConsole.html)
+  - Hedwig is a publish-subscribe system designed to carry large amounts of data across the
internet in a guaranteed-delivery
+    fashion from those who produce it (publishers) to those who are interested in it (subscribers).
+
+### [Apache Helix](http://helix.apache.org/)
+  - Apache Helix is a cluster management framework for partitioned and replicated distributed
resources.
+  - It provides a generic way of automatically managing the resources in a cluster. Helix
acts as a decision subsystem for the cluster, and is responsible for the following tasks and
many more:
+    - Automating the reassignment of resources to the nodes
+    - Handling node failure detection and recovery
+    - Dynamic cluster reconfiguration (node and resource addition/deletion)
+    - Scheduling of maintenance tasks (backups, index rebuilds, and so on)
+    - Maintaining load balancing and flow control in the cluster
+    In order to store the current cluster state, Helix needs a distributed and highly available
configuration or cluster metadata store, for which it uses ZooKeeper.
+  - ZooKeeper provides Helix with the following capabilities:
+    - This framework represents the PERSISTENT state, which remains until it's removed
+    - This framework also represents the TRANSIENT/EPHEMERAL state, which goes away when
the process that created the state leaves the cluster
+    - This framework notifies the subsystem when there is a change in the PERSISTENT and
EPHEMERAL state of the cluster
+  - Helix also allows simple lookups of task assignments through the configuration store
built on top of ZooKeeper. Through this, clients can look up where the tasks are currently
assigned.
+    This way, Helix can also provide a service discovery registry.[21]
+
+### [Apache Kafka](https://kafka.apache.org/)
+  - Kafka is a distributed publish/subscribe messaging system
+  - Apache Kafka relies on ZooKeeper for the following things:
+    - **Controller election**
+    The controller is one of the most important broking entity in a Kafka ecosystem, and
it also has the responsibility
+    to maintain the leader-follower relationship across all the partitions. If a node by
some reason is shutting down,
+    it’s the controller’s responsibility to tell all the replicas to act as partition
leaders in order to fulfill the
+    duties of the partition leaders on the node that is about to fail. So, whenever a node
shuts down, a new controller
+    can be elected and it can also be made sure that at any given time, there is only one
controller and all the follower nodes have agreed on that.
+    - **Configuration Of Topics**
+    The configuration regarding all the topics including the list of existing topics, the
number of partitions for each topic,
+    the location of all the replicas, list of configuration overrides for all topics and
which node is the preferred leader, etc.
+    - **Access control lists**
+    Access control lists or ACLs for all the topics are also maintained within Zookeeper.
+    - **Membership of the cluster**
+    Zookeeper also maintains a list of all the brokers that are functioning at any given
moment and are a part of the cluster.[9]
+
+### [Apache Mesos](http://mesos.apache.org/)
+  - Apache Mesos abstracts CPU, memory, storage, and other compute resources away from machines
(physical or virtual),
+    enabling fault-tolerant and elastic distributed systems to easily be built and run effectively.
+  - Mesos has a high-availability mode that uses multiple Mesos masters: one active master
(called the leader or leading master)
+    and several backups in case it fails. The masters elect the leader, with Apache ZooKeeper
both coordinating the election
+    and handling leader detection by masters, agents, and scheduler drivers.[10]
+
+### [Apache S4](https://github.com/apache/incubator-retired-s4)
+  - S4(**retired** on 2014-06-19[11]) is a general-purpose, distributed, scalable, partially
fault-tolerant, pluggable platform that allows programmers
+    to easily develop applications for processing continuous unbounded streams of data.
+
+### [Apache Solr](https://lucene.apache.org/solr/)
+  - Solr is the popular, blazing-fast, open source enterprise search platform built on Apache
Lucene.
+  - In the "Cloud" edition (v4.x and up) of enterprise search engine Apache Solr, ZooKeeper
is used for configuration,
+    leader election and more[12,13]
+
+### [Apache Spark](https://spark.apache.org/)
+  - Apache Spark is a unified analytics engine for large-scale data processing.
+  - Utilizing ZooKeeper to provide leader election and some state storage, you can launch
multiple Masters in your cluster connected to the same ZooKeeper instance.
+    One will be elected “leader” and the others will remain in standby mode. If the current
leader dies, another Master will be elected,
+    recover the old Master’s state, and then resume scheduling[14]
+
+
+## Companies
+
+### [101tec](http://101tec.com/)
 
 Review comment:
   this should be removed.

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