3. Validating HA Configuration

Verify the state of each NameNode, using one the following methods:
1. Open the web page for each NameNode in a browser, using the configured URL.
  The HA state of the NameNode should appear in the configured address label; for example, NameNode example.com.8020 (standby).
  
  Note
  The NameNode state may be standby or active. After bootstrapping, the HA NameNode state is initially standby.
2. Query the state of a NameNode using JMX(tag.HAState)
3. Query the service state using the following command:
```
 hdfs haadmin -getServiceState
```

Verify automatic failover.

Locate the Active NameNode.
Use the NameNode web UI to check the status for each NameNode host machine.

Cause a failure on the Active NameNode host machine.

Turn off automatic restart of the service.
1. In the Windows Services pane, locate the Apache Hadoop NameNode service, right-click, and choose Properties.
2. On the Recovery tab, select Take No Action for First, Second, and Subsequent Failures, then choose Apply.

Simulate a JVM crash. For example, you can use the following command to simulate a JVM crash:

 taskkill.exe /t /f /im namenode.exe

Alternatively, power-cycle the machine or unplug its network interface to simulate an outage. The Standby NameNode state should become Active within several seconds.

	Note
	The time required to detect a failure and trigger a failover depends on the configuration of `ha.zookeeper.session-timeout.ms` property. The default value is 5 seconds.

Verify that the Standby NameNode state is Active.
1. If a standby NameNode does not activate, verify that the HA settings are configured correctly.
2. To diagnose issues, check log files for zkfc daemons and NameNode daemons.

Legal notices

	Note
	The NameNode state may be `standby` or `active`. After bootstrapping, the HA NameNode state is initially `standby`.