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From aengin...@apache.org
Subject [33/48] hadoop git commit: HDFS-9005. Provide support for upgrade domain script. (Ming Ma via Lei Xu)
Date Mon, 28 Mar 2016 17:36:01 GMT
HDFS-9005. Provide support for upgrade domain script. (Ming Ma via Lei Xu)


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/4fcfea71
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/4fcfea71
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/4fcfea71

Branch: refs/heads/HDFS-7240
Commit: 4fcfea71bfb16295f3a661e712d66351a1edc55e
Parents: 9a09200
Author: Lei Xu <lei@apache.org>
Authored: Fri Mar 25 17:09:12 2016 -0700
Committer: Lei Xu <lei@apache.org>
Committed: Fri Mar 25 17:09:12 2016 -0700

----------------------------------------------------------------------
 .../hdfs/protocol/DatanodeAdminProperties.java  | 100 ++++++++
 .../hdfs/util/CombinedHostsFileReader.java      |  76 ++++++
 .../hdfs/util/CombinedHostsFileWriter.java      |  69 +++++
 .../CombinedHostFileManager.java                | 250 +++++++++++++++++++
 .../blockmanagement/HostConfigManager.java      |  80 ++++++
 .../hdfs/server/blockmanagement/HostSet.java    | 114 +++++++++
 .../TestUpgradeDomainBlockPlacementPolicy.java  | 169 +++++++++++++
 .../hadoop/hdfs/util/HostsFileWriter.java       | 122 +++++++++
 .../hdfs/util/TestCombinedHostsFileReader.java  |  79 ++++++
 .../src/test/resources/dfs.hosts.json           |   5 +
 10 files changed, 1064 insertions(+)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/DatanodeAdminProperties.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/DatanodeAdminProperties.java
b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/DatanodeAdminProperties.java
new file mode 100644
index 0000000..9f7b983
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/DatanodeAdminProperties.java
@@ -0,0 +1,100 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo.AdminStates;
+
+/**
+ * The class describes the configured admin properties for a datanode.
+ *
+ * It is the static configuration specified by administrators via dfsadmin
+ * command; different from the runtime state. CombinedHostFileManager uses
+ * the class to deserialize the configurations from json-based file format.
+ *
+ * To decommission a node, use AdminStates.DECOMMISSIONED.
+ */
+public class DatanodeAdminProperties {
+  private String hostName;
+  private int port;
+  private String upgradeDomain;
+  private AdminStates adminState = AdminStates.NORMAL;
+
+  /**
+   * Return the host name of the datanode.
+   * @return the host name of the datanode.
+   */
+  public String getHostName() {
+    return hostName;
+  }
+
+  /**
+   * Set the host name of the datanode.
+   * @param hostName the host name of the datanode.
+   */
+  public void setHostName(final String hostName) {
+    this.hostName = hostName;
+  }
+
+  /**
+   * Get the port number of the datanode.
+   * @return the port number of the datanode.
+   */
+  public int getPort() {
+    return port;
+  }
+
+  /**
+   * Set the port number of the datanode.
+   * @param port the port number of the datanode.
+   */
+  public void setPort(final int port) {
+    this.port = port;
+  }
+
+  /**
+   * Get the upgrade domain of the datanode.
+   * @return the upgrade domain of the datanode.
+   */
+  public String getUpgradeDomain() {
+    return upgradeDomain;
+  }
+
+  /**
+   * Set the upgrade domain of the datanode.
+   * @param upgradeDomain the upgrade domain of the datanode.
+   */
+  public void setUpgradeDomain(final String upgradeDomain) {
+    this.upgradeDomain = upgradeDomain;
+  }
+
+  /**
+   * Get the admin state of the datanode.
+   * @return the admin state of the datanode.
+   */
+  public AdminStates getAdminState() {
+    return adminState;
+  }
+
+  /**
+   * Set the admin state of the datanode.
+   * @param adminState the admin state of the datanode.
+   */
+  public void setAdminState(final AdminStates adminState) {
+    this.adminState = adminState;
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileReader.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileReader.java
b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileReader.java
new file mode 100644
index 0000000..33acb91
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileReader.java
@@ -0,0 +1,76 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.hdfs.util;
+
+import java.io.FileInputStream;
+import java.io.InputStreamReader;
+import java.io.IOException;
+import java.io.Reader;
+
+import java.util.Iterator;
+import java.util.Set;
+import java.util.HashSet;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.codehaus.jackson.JsonFactory;
+import org.codehaus.jackson.map.ObjectMapper;
+
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+
+/**
+ * Reader support for JSON based datanode configuration, an alternative
+ * to the exclude/include files configuration.
+ * The JSON file format is the array of elements where each element
+ * in the array describes the properties of a datanode. The properties of
+ * a datanode is defined in {@link DatanodeAdminProperties}. For example,
+ *
+ * {"hostName": "host1"}
+ * {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"}
+ * {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ */
+@InterfaceAudience.LimitedPrivate({"HDFS"})
+@InterfaceStability.Unstable
+public final class CombinedHostsFileReader {
+  private CombinedHostsFileReader() {
+  }
+
+  /**
+   * Deserialize a set of DatanodeAdminProperties from a json file.
+   * @param hostsFile the input json file to read from.
+   * @return the set of DatanodeAdminProperties
+   * @throws IOException
+   */
+  public static Set<DatanodeAdminProperties>
+      readFile(final String hostsFile) throws IOException {
+    HashSet<DatanodeAdminProperties> allDNs = new HashSet<>();
+    ObjectMapper mapper = new ObjectMapper();
+    try (Reader input =
+         new InputStreamReader(new FileInputStream(hostsFile), "UTF-8")) {
+      Iterator<DatanodeAdminProperties> iterator =
+          mapper.readValues(new JsonFactory().createJsonParser(input),
+              DatanodeAdminProperties.class);
+      while (iterator.hasNext()) {
+        DatanodeAdminProperties properties = iterator.next();
+        allDNs.add(properties);
+      }
+    }
+    return allDNs;
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileWriter.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileWriter.java
b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileWriter.java
new file mode 100644
index 0000000..ea70be2
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/CombinedHostsFileWriter.java
@@ -0,0 +1,69 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.hdfs.util;
+
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+
+import java.util.Set;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.codehaus.jackson.map.ObjectMapper;
+
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+
+/**
+ * Writer support for JSON based datanode configuration, an alternative
+ * to the exclude/include files configuration.
+ * The JSON file format is the array of elements where each element
+ * in the array describes the properties of a datanode. The properties of
+ * a datanode is defined in {@link DatanodeAdminProperties}. For example,
+ *
+ * {"hostName": "host1"}
+ * {"hostName": "host2", "port": 50, "upgradeDomain": "ud0"}
+ * {"hostName": "host3", "port": 0, "adminState": "DECOMMISSIONED"}
+ */
+@InterfaceAudience.LimitedPrivate({"HDFS"})
+@InterfaceStability.Unstable
+public final class CombinedHostsFileWriter {
+  private CombinedHostsFileWriter() {
+  }
+
+  /**
+   * Serialize a set of DatanodeAdminProperties to a json file.
+   * @param hostsFile the json file name.
+   * @param allDNs the set of DatanodeAdminProperties
+   * @throws IOException
+   */
+  public static void writeFile(final String hostsFile,
+      final Set<DatanodeAdminProperties> allDNs) throws IOException {
+    StringBuilder configs = new StringBuilder();
+    try (Writer output =
+       new OutputStreamWriter(new FileOutputStream(hostsFile), "UTF-8")) {
+      for (DatanodeAdminProperties datanodeAdminProperties: allDNs) {
+        ObjectMapper mapper = new ObjectMapper();
+        configs.append(mapper.writeValueAsString(datanodeAdminProperties));
+      }
+      output.write(configs.toString());
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java
new file mode 100644
index 0000000..3e913b9
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java
@@ -0,0 +1,250 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.server.blockmanagement;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Multimap;
+import com.google.common.collect.UnmodifiableIterator;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Collections2;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo.AdminStates;
+
+import java.io.IOException;
+
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Set;
+
+import com.google.common.base.Predicate;
+
+import org.apache.hadoop.hdfs.util.CombinedHostsFileReader;
+
+/**
+ * This class manages datanode configuration using a json file.
+ * Please refer to {@link CombinedHostsFileReader} for the json format.
+ * <p/>
+ * <p/>
+ * Entries may or may not specify a port.  If they don't, we consider
+ * them to apply to every DataNode on that host. The code canonicalizes the
+ * entries into IP addresses.
+ * <p/>
+ * <p/>
+ * The code ignores all entries that the DNS fails to resolve their IP
+ * addresses. This is okay because by default the NN rejects the registrations
+ * of DNs when it fails to do a forward and reverse lookup. Note that DNS
+ * resolutions are only done during the loading time to minimize the latency.
+ */
+public class CombinedHostFileManager extends HostConfigManager {
+  private static final Logger LOG = LoggerFactory.getLogger(
+      CombinedHostFileManager.class);
+  private Configuration conf;
+  private HostProperties hostProperties = new HostProperties();
+
+  static class HostProperties {
+    private Multimap<InetAddress, DatanodeAdminProperties> allDNs =
+        HashMultimap.create();
+    // optimization. If every node in the file isn't in service, it implies
+    // any node is allowed to register with nn. This is equivalent to having
+    // an empty "include" file.
+    private boolean emptyInServiceNodeLists = true;
+    synchronized void add(InetAddress addr,
+        DatanodeAdminProperties properties) {
+      allDNs.put(addr, properties);
+      if (properties.getAdminState().equals(
+          AdminStates.NORMAL)) {
+        emptyInServiceNodeLists = false;
+      }
+    }
+
+    // If the includes list is empty, act as if everything is in the
+    // includes list.
+    synchronized boolean isIncluded(final InetSocketAddress address) {
+      return emptyInServiceNodeLists || Iterables.any(
+          allDNs.get(address.getAddress()),
+          new Predicate<DatanodeAdminProperties>() {
+            public boolean apply(DatanodeAdminProperties input) {
+              return input.getPort() == 0 ||
+                  input.getPort() == address.getPort();
+            }
+          });
+    }
+
+    synchronized boolean isExcluded(final InetSocketAddress address) {
+      return Iterables.any(allDNs.get(address.getAddress()),
+          new Predicate<DatanodeAdminProperties>() {
+            public boolean apply(DatanodeAdminProperties input) {
+              return input.getAdminState().equals(
+                  AdminStates.DECOMMISSIONED) &&
+                  (input.getPort() == 0 ||
+                      input.getPort() == address.getPort());
+            }
+          });
+    }
+
+    synchronized String getUpgradeDomain(final InetSocketAddress address) {
+      Iterable<DatanodeAdminProperties> datanode = Iterables.filter(
+          allDNs.get(address.getAddress()),
+          new Predicate<DatanodeAdminProperties>() {
+            public boolean apply(DatanodeAdminProperties input) {
+              return (input.getPort() == 0 ||
+                  input.getPort() == address.getPort());
+            }
+          });
+      return datanode.iterator().hasNext() ?
+          datanode.iterator().next().getUpgradeDomain() : null;
+    }
+
+    Iterable<InetSocketAddress> getIncludes() {
+      return new Iterable<InetSocketAddress>() {
+        @Override
+        public Iterator<InetSocketAddress> iterator() {
+            return new HostIterator(allDNs.entries());
+        }
+      };
+    }
+
+    Iterable<InetSocketAddress> getExcludes() {
+      return new Iterable<InetSocketAddress>() {
+        @Override
+        public Iterator<InetSocketAddress> iterator() {
+          return new HostIterator(
+              Collections2.filter(allDNs.entries(),
+                  new Predicate<java.util.Map.Entry<InetAddress,
+                      DatanodeAdminProperties>>() {
+                    public boolean apply(java.util.Map.Entry<InetAddress,
+                        DatanodeAdminProperties> entry) {
+                      return entry.getValue().getAdminState().equals(
+                          AdminStates.DECOMMISSIONED);
+                    }
+                  }
+              ));
+        }
+      };
+    }
+
+    static class HostIterator extends UnmodifiableIterator<InetSocketAddress> {
+      private final Iterator<Map.Entry<InetAddress,
+          DatanodeAdminProperties>> it;
+      public HostIterator(Collection<java.util.Map.Entry<InetAddress,
+          DatanodeAdminProperties>> nodes) {
+        this.it = nodes.iterator();
+      }
+      @Override
+      public boolean hasNext() {
+        return it.hasNext();
+      }
+
+      @Override
+      public InetSocketAddress next() {
+        Map.Entry<InetAddress, DatanodeAdminProperties> e = it.next();
+        return new InetSocketAddress(e.getKey(), e.getValue().getPort());
+      }
+    }
+  }
+
+  @Override
+  public Iterable<InetSocketAddress> getIncludes() {
+    return hostProperties.getIncludes();
+  }
+
+  @Override
+  public Iterable<InetSocketAddress> getExcludes() {
+    return hostProperties.getExcludes();
+  }
+
+  @Override
+  public void setConf(Configuration conf) {
+    this.conf = conf;
+  }
+
+  @Override
+  public Configuration getConf() {
+    return conf;
+  }
+
+  @Override
+  public void refresh() throws IOException {
+    refresh(conf.get(DFSConfigKeys.DFS_HOSTS, ""));
+  }
+  private void refresh(final String hostsFile) throws IOException {
+    HostProperties hostProps = new HostProperties();
+    Set<DatanodeAdminProperties> all =
+        CombinedHostsFileReader.readFile(hostsFile);
+    for(DatanodeAdminProperties properties : all) {
+      InetSocketAddress addr = parseEntry(hostsFile,
+          properties.getHostName(), properties.getPort());
+      if (addr != null) {
+        hostProps.add(addr.getAddress(), properties);
+      }
+    }
+    refresh(hostProps);
+  }
+
+  @VisibleForTesting
+  static InetSocketAddress parseEntry(final String fn, final String hostName,
+      final int port) {
+    InetSocketAddress addr = new InetSocketAddress(hostName, port);
+    if (addr.isUnresolved()) {
+      LOG.warn("Failed to resolve {} in {}. ", hostName, fn);
+      return null;
+    }
+    return addr;
+  }
+
+  @Override
+  public synchronized boolean isIncluded(final DatanodeID dn) {
+    return hostProperties.isIncluded(dn.getResolvedAddress());
+  }
+
+  @Override
+  public synchronized boolean isExcluded(final DatanodeID dn) {
+    return isExcluded(dn.getResolvedAddress());
+  }
+
+  private boolean isExcluded(final InetSocketAddress address) {
+    return hostProperties.isExcluded(address);
+  }
+
+  @Override
+  public synchronized String getUpgradeDomain(final DatanodeID dn) {
+    return hostProperties.getUpgradeDomain(dn.getResolvedAddress());
+  }
+
+  /**
+   * Set the properties lists by the new instances. The
+   * old instance is discarded.
+   * @param hostProperties the new properties list
+   */
+  @VisibleForTesting
+  private void refresh(final HostProperties hostProperties) {
+    synchronized (this) {
+      this.hostProperties = hostProperties;
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostConfigManager.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostConfigManager.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostConfigManager.java
new file mode 100644
index 0000000..f28ed29
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostConfigManager.java
@@ -0,0 +1,80 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.server.blockmanagement;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.Configurable;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+
+/**
+ * This interface abstracts how datanode configuration is managed.
+ *
+ * Each implementation defines its own way to persist the configuration.
+ * For example, it can use one JSON file to store the configs for all
+ * datanodes; or it can use one file to store in-service datanodes and another
+ * file to store decommission-requested datanodes.
+ *
+ * These files control which DataNodes the NameNode expects to see in the
+ * cluster.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Unstable
+public abstract class HostConfigManager implements Configurable {
+
+  /**
+   * Return all the datanodes that are allowed to connect to the namenode.
+   * @return Iterable of all datanodes
+   */
+  public abstract Iterable<InetSocketAddress> getIncludes();
+
+  /**
+   * Return all datanodes that should be in decommissioned state.
+   * @return Iterable of those datanodes
+   */
+  public abstract Iterable<InetSocketAddress> getExcludes();
+
+  /**
+   * Check if a datanode is allowed to connect the namenode.
+   * @param dn the DatanodeID of the datanode
+   * @return boolean if dn is allowed to connect the namenode.
+   */
+  public abstract boolean isIncluded(DatanodeID dn);
+
+  /**
+   * Check if a datanode needs to be decommissioned.
+   * @param dn the DatanodeID of the datanode
+   * @return boolean if dn needs to be decommissioned.
+   */
+  public abstract boolean isExcluded(DatanodeID dn);
+
+  /**
+   * Reload the configuration.
+   */
+  public abstract void refresh() throws IOException;
+
+  /**
+   * Get the upgrade domain of a datanode.
+   * @param dn the DatanodeID of the datanode
+   * @return the upgrade domain of dn.
+   */
+  public abstract String getUpgradeDomain(DatanodeID dn);
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostSet.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostSet.java
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostSet.java
new file mode 100644
index 0000000..958557b
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HostSet.java
@@ -0,0 +1,114 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.server.blockmanagement;
+
+import com.google.common.base.Function;
+import com.google.common.base.Joiner;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Iterators;
+import com.google.common.collect.Multimap;
+import com.google.common.collect.UnmodifiableIterator;
+
+import javax.annotation.Nullable;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.Map;
+
+
+/**
+ * The HostSet allows efficient queries on matching wildcard addresses.
+ * <p/>
+ * For InetSocketAddress A and B with the same host address,
+ * we define a partial order between A and B, A <= B iff A.getPort() == B
+ * .getPort() || B.getPort() == 0.
+ */
+public class HostSet implements Iterable<InetSocketAddress> {
+  // Host -> lists of ports
+  private final Multimap<InetAddress, Integer> addrs = HashMultimap.create();
+
+  /**
+   * The function that checks whether there exists an entry foo in the set
+   * so that foo <= addr.
+   */
+  boolean matchedBy(InetSocketAddress addr) {
+    Collection<Integer> ports = addrs.get(addr.getAddress());
+    return addr.getPort() == 0 ? !ports.isEmpty() : ports.contains(addr
+        .getPort());
+  }
+
+  /**
+   * The function that checks whether there exists an entry foo in the set
+   * so that addr <= foo.
+   */
+  boolean match(InetSocketAddress addr) {
+    int port = addr.getPort();
+    Collection<Integer> ports = addrs.get(addr.getAddress());
+    boolean exactMatch = ports.contains(port);
+    boolean genericMatch = ports.contains(0);
+    return exactMatch || genericMatch;
+  }
+
+  boolean isEmpty() {
+    return addrs.isEmpty();
+  }
+
+  int size() {
+    return addrs.size();
+  }
+
+  void add(InetSocketAddress addr) {
+    Preconditions.checkArgument(!addr.isUnresolved());
+    addrs.put(addr.getAddress(), addr.getPort());
+  }
+
+  @Override
+  public Iterator<InetSocketAddress> iterator() {
+    return new UnmodifiableIterator<InetSocketAddress>() {
+      private final Iterator<Map.Entry<InetAddress,
+          Integer>> it = addrs.entries().iterator();
+
+      @Override
+      public boolean hasNext() {
+        return it.hasNext();
+      }
+
+      @Override
+      public InetSocketAddress next() {
+        Map.Entry<InetAddress, Integer> e = it.next();
+        return new InetSocketAddress(e.getKey(), e.getValue());
+      }
+    };
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder("HostSet(");
+    Joiner.on(",").appendTo(sb, Iterators.transform(iterator(),
+        new Function<InetSocketAddress, String>() {
+          @Override
+          public String apply(@Nullable InetSocketAddress addr) {
+            assert addr != null;
+            return addr.getAddress().getHostAddress() + ":" + addr.getPort();
+          }
+        }));
+    return sb.append(")").toString();
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestUpgradeDomainBlockPlacementPolicy.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestUpgradeDomainBlockPlacementPolicy.java
b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestUpgradeDomainBlockPlacementPolicy.java
new file mode 100644
index 0000000..cc14fcb
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestUpgradeDomainBlockPlacementPolicy.java
@@ -0,0 +1,169 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CreateFlag;
+import org.apache.hadoop.fs.permission.FsPermission;
+import org.apache.hadoop.fs.permission.PermissionStatus;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.HdfsFileStatus;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy;
+import org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyWithUpgradeDomain;
+import org.apache.hadoop.hdfs.server.blockmanagement.CombinedHostFileManager;
+import org.apache.hadoop.hdfs.server.blockmanagement.HostConfigManager;
+import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
+import org.apache.hadoop.hdfs.util.HostsFileWriter;
+import org.apache.hadoop.net.StaticMapping;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * End-to-end test case for upgrade domain
+ * The test configs upgrade domain for nodes via admin json
+ * config file and put some nodes to decommission state.
+ * The test then verifies replicas are placed on the nodes that
+ * satisfy the upgrade domain policy.
+ *
+ */
+public class TestUpgradeDomainBlockPlacementPolicy {
+
+  private static final short REPLICATION_FACTOR = (short) 3;
+  private static final int DEFAULT_BLOCK_SIZE = 1024;
+  static final String[] racks =
+      { "/RACK1", "/RACK1", "/RACK1", "/RACK2", "/RACK2", "/RACK2" };
+  /**
+   *  Use host names that can be resolved (
+   *  InetSocketAddress#isUnresolved == false). Otherwise,
+   *  CombinedHostFileManager won't allow those hosts.
+   */
+  static final String[] hosts =
+      { "127.0.0.1", "127.0.0.1", "127.0.0.1", "127.0.0.1",
+          "127.0.0.1", "127.0.0.1" };
+  static final String[] upgradeDomains =
+      { "ud1", "ud2", "ud3", "ud1", "ud2", "ud3" };
+  static final Set<DatanodeID> expectedDatanodeIDs = new HashSet<>();
+  private MiniDFSCluster cluster = null;
+  private NamenodeProtocols nameNodeRpc = null;
+  private FSNamesystem namesystem = null;
+  private PermissionStatus perm = null;
+
+  @Before
+  public void setup() throws IOException {
+    StaticMapping.resetMap();
+    Configuration conf = new HdfsConfiguration();
+    conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, DEFAULT_BLOCK_SIZE);
+    conf.setInt(DFSConfigKeys.DFS_BYTES_PER_CHECKSUM_KEY, DEFAULT_BLOCK_SIZE / 2);
+    conf.setClass(DFSConfigKeys.DFS_BLOCK_REPLICATOR_CLASSNAME_KEY,
+        BlockPlacementPolicyWithUpgradeDomain.class,
+        BlockPlacementPolicy.class);
+    conf.setClass(DFSConfigKeys.DFS_NAMENODE_HOSTS_PROVIDER_CLASSNAME_KEY,
+        CombinedHostFileManager.class, HostConfigManager.class);
+    HostsFileWriter hostsFileWriter = new HostsFileWriter();
+    hostsFileWriter.initialize(conf, "temp/upgradedomainpolicy");
+
+    cluster = new MiniDFSCluster.Builder(conf).numDataNodes(6).racks(racks)
+        .hosts(hosts).build();
+    cluster.waitActive();
+    nameNodeRpc = cluster.getNameNodeRpc();
+    namesystem = cluster.getNamesystem();
+    perm = new PermissionStatus("TestDefaultBlockPlacementPolicy", null,
+        FsPermission.getDefault());
+    refreshDatanodeAdminProperties(hostsFileWriter);
+    hostsFileWriter.cleanup();
+  }
+
+  @After
+  public void teardown() {
+    if (cluster != null) {
+      cluster.shutdown();
+      cluster = null;
+    }
+  }
+
+  /**
+   * Define admin properties for these datanodes as follows.
+   * dn0 and dn3 have upgrade domain ud1.
+   * dn1 and dn4 have upgrade domain ud2.
+   * dn2 and dn5 have upgrade domain ud3.
+   * dn0 and dn5 are decommissioned.
+   * Given dn0, dn1 and dn2 are on rack1 and dn3, dn4 and dn5 are on
+   * rack2. Then any block's replicas should be on either
+   * {dn1, dn2, d3} or {dn2, dn3, dn4}.
+   */
+  private void refreshDatanodeAdminProperties(HostsFileWriter hostsFileWriter)
+      throws IOException {
+    DatanodeAdminProperties[] datanodes = new DatanodeAdminProperties[
+        hosts.length];
+    for (int i = 0; i < hosts.length; i++) {
+      datanodes[i] = new DatanodeAdminProperties();
+      DatanodeID datanodeID = cluster.getDataNodes().get(i).getDatanodeId();
+      datanodes[i].setHostName(datanodeID.getHostName());
+      datanodes[i].setPort(datanodeID.getXferPort());
+      datanodes[i].setUpgradeDomain(upgradeDomains[i]);
+    }
+    datanodes[0].setAdminState(DatanodeInfo.AdminStates.DECOMMISSIONED);
+    datanodes[5].setAdminState(DatanodeInfo.AdminStates.DECOMMISSIONED);
+    hostsFileWriter.initIncludeHosts(datanodes);
+    cluster.getFileSystem().refreshNodes();
+
+    expectedDatanodeIDs.add(cluster.getDataNodes().get(2).getDatanodeId());
+    expectedDatanodeIDs.add(cluster.getDataNodes().get(3).getDatanodeId());
+  }
+
+  @Test
+  public void testPlacement() throws Exception {
+    String clientMachine = "127.0.0.1";
+    for (int i = 0; i < 5; i++) {
+      String src = "/test-" + i;
+      // Create the file with client machine
+      HdfsFileStatus fileStatus = namesystem.startFile(src, perm,
+          clientMachine, clientMachine, EnumSet.of(CreateFlag.CREATE), true,
+          REPLICATION_FACTOR, DEFAULT_BLOCK_SIZE, null, false);
+      LocatedBlock locatedBlock = nameNodeRpc.addBlock(src, clientMachine,
+          null, null, fileStatus.getFileId(), null);
+
+      assertEquals("Block should be allocated sufficient locations",
+          REPLICATION_FACTOR, locatedBlock.getLocations().length);
+      Set<DatanodeInfo> locs = new HashSet<>(Arrays.asList(
+          locatedBlock.getLocations()));
+      for (DatanodeID datanodeID : expectedDatanodeIDs) {
+        locs.contains(datanodeID);
+      }
+
+      nameNodeRpc.abandonBlock(locatedBlock.getBlock(), fileStatus.getFileId(),
+          src, clientMachine);
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/HostsFileWriter.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/HostsFileWriter.java
b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/HostsFileWriter.java
new file mode 100644
index 0000000..cd5ae95
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/HostsFileWriter.java
@@ -0,0 +1,122 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.hdfs.util;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashSet;
+
+
+import org.apache.commons.io.FileUtils;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSTestUtil;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.server.blockmanagement.HostConfigManager;
+import org.apache.hadoop.hdfs.server.blockmanagement.HostFileManager;
+
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo.AdminStates;
+
+import static org.junit.Assert.assertTrue;
+
+public class HostsFileWriter {
+  private FileSystem localFileSys;
+  private Path fullDir;
+  private Path excludeFile;
+  private Path includeFile;
+  private Path combinedFile;
+  private boolean isLegacyHostsFile = false;
+
+  public void initialize(Configuration conf, String dir) throws IOException {
+    localFileSys = FileSystem.getLocal(conf);
+    Path workingDir = new Path(MiniDFSCluster.getBaseDirectory());
+    this.fullDir = new Path(workingDir, dir);
+    assertTrue(localFileSys.mkdirs(this.fullDir));
+
+    if (conf.getClass(
+        DFSConfigKeys.DFS_NAMENODE_HOSTS_PROVIDER_CLASSNAME_KEY,
+            HostFileManager.class, HostConfigManager.class).equals(
+                HostFileManager.class)) {
+      isLegacyHostsFile = true;
+    }
+    if (isLegacyHostsFile) {
+      excludeFile = new Path(fullDir, "exclude");
+      includeFile = new Path(fullDir, "include");
+      DFSTestUtil.writeFile(localFileSys, excludeFile, "");
+      DFSTestUtil.writeFile(localFileSys, includeFile, "");
+      conf.set(DFSConfigKeys.DFS_HOSTS_EXCLUDE, excludeFile.toUri().getPath());
+      conf.set(DFSConfigKeys.DFS_HOSTS, includeFile.toUri().getPath());
+    } else {
+      combinedFile = new Path(fullDir, "all");
+      conf.set(DFSConfigKeys.DFS_HOSTS, combinedFile.toString());
+    }
+  }
+
+  public void initExcludeHost(String hostNameAndPort) throws IOException {
+    if (isLegacyHostsFile) {
+      DFSTestUtil.writeFile(localFileSys, excludeFile, hostNameAndPort);
+    } else {
+      DatanodeAdminProperties dn = new DatanodeAdminProperties();
+      String [] hostAndPort = hostNameAndPort.split(":");
+      dn.setHostName(hostAndPort[0]);
+      dn.setPort(Integer.parseInt(hostAndPort[1]));
+      dn.setAdminState(AdminStates.DECOMMISSIONED);
+      HashSet<DatanodeAdminProperties> allDNs = new HashSet<>();
+      allDNs.add(dn);
+      CombinedHostsFileWriter.writeFile(combinedFile.toString(), allDNs);
+    }
+  }
+
+  public void initIncludeHosts(String[] hostNameAndPorts) throws IOException {
+    StringBuilder includeHosts = new StringBuilder();
+    if (isLegacyHostsFile) {
+      for(String hostNameAndPort : hostNameAndPorts) {
+        includeHosts.append(hostNameAndPort).append("\n");
+      }
+      DFSTestUtil.writeFile(localFileSys, includeFile,
+          includeHosts.toString());
+    } else {
+      HashSet<DatanodeAdminProperties> allDNs = new HashSet<>();
+      for(String hostNameAndPort : hostNameAndPorts) {
+        String[] hostAndPort = hostNameAndPort.split(":");
+        DatanodeAdminProperties dn = new DatanodeAdminProperties();
+        dn.setHostName(hostAndPort[0]);
+        dn.setPort(Integer.parseInt(hostAndPort[1]));
+        allDNs.add(dn);
+      }
+      CombinedHostsFileWriter.writeFile(combinedFile.toString(), allDNs);
+    }
+  }
+
+  public void initIncludeHosts(DatanodeAdminProperties[] datanodes)
+      throws IOException {
+    CombinedHostsFileWriter.writeFile(combinedFile.toString(),
+        new HashSet<>(Arrays.asList(datanodes)));
+  }
+
+  public void cleanup() throws IOException {
+    if (localFileSys.exists(fullDir)) {
+      FileUtils.deleteQuietly(new File(fullDir.toUri().getPath()));
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java
b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java
new file mode 100644
index 0000000..c3946e4
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java
@@ -0,0 +1,79 @@
+/**
+ * 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.
+ */
+package org.apache.hadoop.hdfs.util;
+
+import java.io.File;
+import java.io.FileWriter;
+
+import java.util.Set;
+
+import org.apache.hadoop.hdfs.protocol.DatanodeAdminProperties;
+import org.junit.Before;
+import org.junit.After;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/*
+ * Test for JSON based HostsFileReader
+ */
+public class TestCombinedHostsFileReader {
+
+  // Using /test/build/data/tmp directory to store temporary files
+  static final String HOSTS_TEST_DIR = new File(System.getProperty(
+      "test.build.data", "/tmp")).getAbsolutePath();
+  File NEW_FILE = new File(HOSTS_TEST_DIR, "dfs.hosts.new.json");
+
+  static final String TEST_CACHE_DATA_DIR =
+      System.getProperty("test.cache.data", "build/test/cache");
+  File EXISTING_FILE = new File(TEST_CACHE_DATA_DIR, "dfs.hosts.json");
+
+  @Before
+  public void setUp() throws Exception {
+  }
+
+  @After
+  public void tearDown() throws Exception {
+    // Delete test file after running tests
+    NEW_FILE.delete();
+
+  }
+
+  /*
+   * Load the existing test json file
+   */
+  @Test
+  public void testLoadExistingJsonFile() throws Exception {
+    Set<DatanodeAdminProperties> all =
+        CombinedHostsFileReader.readFile(EXISTING_FILE.getAbsolutePath());
+    assertEquals(5, all.size());
+  }
+
+  /*
+   * Test empty json config file
+   */
+  @Test
+  public void testEmptyCombinedHostsFileReader() throws Exception {
+    FileWriter hosts = new FileWriter(NEW_FILE);
+    hosts.write("");
+    hosts.close();
+    Set<DatanodeAdminProperties> all =
+        CombinedHostsFileReader.readFile(NEW_FILE.getAbsolutePath());
+    assertEquals(0, all.size());
+  }
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/4fcfea71/hadoop-hdfs-project/hadoop-hdfs/src/test/resources/dfs.hosts.json
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/resources/dfs.hosts.json b/hadoop-hdfs-project/hadoop-hdfs/src/test/resources/dfs.hosts.json
new file mode 100644
index 0000000..64fca48
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/resources/dfs.hosts.json
@@ -0,0 +1,5 @@
+{"hostName": "host1"}
+{"hostName": "host2", "upgradeDomain": "ud0"}
+{"hostName": "host3", "adminState": "DECOMMISSIONED"}
+{"hostName": "host4", "upgradeDomain": "ud2", "adminState": "DECOMMISSIONED"}
+{"hostName": "host5", "port": 8090}


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