hdfs haadmin -failover nn2 nnhdfs haadmin -failover nn2 nn1

1. Stop the NameNode daemon:

   $ sudo service hadoop-hdfs-namenode stop

2. Stop the ZKFC daemon if it is running:

   $ sudo service hadoop-hdfs-zkfc stop

3. Stop the JournalNode daemon if it is running:

   $ sudo service hadoop-hdfs-journalnode stop 

4. Make sure these services are not set to restart on boot. If you are not planning to use nn2 as a NameNode again, you may want remove the services.

hdfs haadmin -failover nn1 nn2-alt

$ sudo service hadoop-hdfs-namenode stop
$ sudo service hadoop-hdfs-namenode start

• In your core-site.xml file:

  fs.defaultFS (formerly fs.default.name)

  Optionally, you may have configured the default path for Hadoop clients to use the HA-enabled logical URI. For example, if you used mycluster as the NameService ID as shown below, this will be the value of the authority portion of all of your HDFS paths.

  <property>
    <name>fs.default.name/name>
    <value>hdfs://mycluster</value>
  </property>

• In your hdfs-site.xml configuration file:

  dfs.nameservices

  <property>
    <name>dfs.nameservices</name>
    <value>mycluster</value>
  </property>

    Note:

  If you are also using HDFS Federation, this configuration setting will include the list of other nameservices, HA or otherwise, as a comma-separated list.

  dfs.ha.namenodes.[nameservice ID]

  A list of comma-separated NameNode IDs used by DataNodes to determine all the NameNodes in the cluster. For example, if you used mycluster as the NameService ID, and you used nn1 and nn2 as the individual IDs of the NameNodes, you would have configured this as follows:

  <property>
    <name>dfs.ha.namenodes.mycluster</name>
    <value>nn1,nn2</value>
  </property>

  dfs.namenode.rpc-address.[nameservice ID]

  For both of the previously-configured NameNode IDs, the full address and RPC port of the NameNode process. For example:

  <property>
    <name>dfs.namenode.rpc-address.mycluster.nn1</name>
    <value>machine1.example.com:8020</value>
  </property>
  <property>
    <name>dfs.namenode.rpc-address.mycluster.nn2</name>
    <value>machine2.example.com:8020</value>
  </property>

    Note:

  You may have similarly configured the servicerpc-address setting.

  dfs.namenode.http-address.[nameservice ID]

  The addresses for both NameNodes' HTTP servers to listen on. For example:

  <property>
    <name>dfs.namenode.http-address.mycluster.nn1</name>
    <value>machine1.example.com:50070</value>
  </property>
  <property>
    <name>dfs.namenode.http-address.mycluster.nn2</name>
    <value>machine2.example.com:50070</value>
  </property>

    Note:

  If you have Hadoop's Kerberos security features enabled, and you use HSFTP, you will have set the https-address similarly for each NameNode.

  dfs.namenode.shared.edits.dir

  The path to the remote shared edits directory which the Standby NameNode uses to stay up-to-date with all the file system changes the Active NameNode makes. You should have configured only one of these directories, mounted read/write on both NameNode machines. The value of this setting should be the absolute path to this directory on the NameNode machines. For example:

  <property>
    <name>dfs.namenode.shared.edits.dir</name>
    <value>file:///mnt/filer1/dfs/ha-name-dir-shared</value>
  </property>

  dfs.client.failover.proxy.provider.[nameservice ID]

  The name of the Java class which the DFS Client uses to determine which NameNode is the current Active, and therefore which NameNode is currently serving client requests. The only implementation which shipped with Hadoop is the ConfiguredFailoverProxyProvider. For example:

  <property>
    <name>dfs.client.failover.proxy.provider.mycluster</name>
    <value>org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider</value>
  </property>

  dfs.ha.fencing.methods - a list of scripts or Java classes which will be used to fence the Active NameNode during a failover.

    Note:

  If you implemented your own custom fencing method, see the org.apache.hadoop.ha.NodeFencer class.

  • The sshfence fencing method

    sshfence - SSH to the Active NameNode and kill the process

    For example:

    <property>
      <name>dfs.ha.fencing.methods</name>
      <value>sshfence</value>
    </property>
    
    <property>
      <name>dfs.ha.fencing.ssh.private-key-files</name>
      <value>/home/exampleuser/.ssh/id_rsa</value>
    </property>

    Optionally, you may have configured a non-standard username or port to perform the SSH, as shown below, and also a timeout, in milliseconds, for the SSH:

    <property>
      <name>dfs.ha.fencing.methods</name>
      <value>sshfence([[username][:port]])</value>
    </property>
    <property>
      <name>dfs.ha.fencing.ssh.connect-timeout</name>
      <value>30000</value>
      <description>
        SSH connection timeout, in milliseconds, to use with the builtin
        sshfence fencer.
      </description>
    </property>

  • The shell fencing method

    shell - run an arbitrary shell command to fence the Active NameNode

    The shell fencing method runs an arbitrary shell command, which you may have configured as shown below:

    <property>
      <name>dfs.ha.fencing.methods</name>
      <value>shell(/path/to/my/script.sh arg1 arg2 ...)</value>
    </property>

• In your hdfs-site.xml:

  <property>
    <name>dfs.ha.automatic-failover.enabled</name>
    <value>true</value>
  </property>

• In your core-site.xml file, add:

  <property>
    <name>ha.zookeeper.quorum</name>
    <value>zk1.example.com:2181,zk2.example.com:2181,zk3.example.com:2181</value>
  </property>