Enabling High Availability for HiveServer2

Configuring Hive

Modify the warden.hs2.conf file as shown below on all the nodes where Hive is installed.
```
services=hs2:all
```

Add the following properties to the hive-site.xml file on all the nodes where HiveServer2 is installed.

Property	Value	Description
`hive.server2.support.dynamic.service.discovery`	`true` (default is `false`)	Set to `true` to enable HiveServer2 dynamic service discovery for its clients.
`hive.server2.zookeeper.namespace`	hiveserver2 (default value)	The parent node in ZooKeeper, which is used by HiveServer2 when supporting dynamic service discovery.
`hive.zookeeper.quorum`	<hostname>:5181,<hostname>:5181,<hostname>:5181	List of ZooKeeper servers to talk to. Used in connection string by JDBC/ODBC clients instead of URI of specific HiveServer2 instance.
`hive.zookeeper.client.port`	5181 (default value)	The port of the ZooKeeper servers to talk to. If the list of Zookeeper servers specified in `hive.zookeeper.quorum` does not contain port numbers and so, this value is used.
`hive.zookeeper.session.timeout`	600000 (default value)	Zookeeper client's session timeout value. The client is disconnected, and as a result, all locks are released if a heartbeat is not sent within the timeout period.

Restart all the nodes where Hive service is installed after updating the configuration.

Connect to HiveServer2 with JDBC/ODBC clients using the following connection string:

jdbc:hive2://<zookeeper_ensemble>/;serviceDiscoveryMode=zooKeeper;
zooKeeperNamespace=<hiveserver2_zookeeper_namespace>

Here:

<zookeeper_ensemble>	Specifies a comma-separated list of ZooKeeper servers that form the ensemble. For example: `<zk_host1>:<zk_port1>,<zk_host2>:<zk_port2>,<zk_host3>:<zk_port3>`.
<hiveserver2_zookeeper_namespace>	Specifies the namespace on Zookeeper under which HiveServer2 znodes are added. The namespace value is configured in `hive.server2.zookeeper.name` space.

Remove a HiveServer2 instance from Zookeeper by running the following commands (in the ZooKeeper command line interface) to deregister the server.

Launch the ZooKeeper command line interface and get the HiveServer2 znode by running the following commands:
```
/opt/mapr/zookeeper/zookeeper-<version>/bin/zkCli.sh -server <ip:port of zookeeper instance>
ls /<hive.server2.zookeeper.namespace>
```
Run the command to deregister HiveServer2. To deregister:
- A particular HiveServer2, run the following command:
```
delete  serverUri=<hostname:port>;version=<hive version>;sequence=<sequence number>
```
  After you deregister the HiveServer2 from Zookeeper, it will not return the deregistered HiveServer2 for new client connections. However, active client sessions are not affected by deregistering the HiveServer2 from Zookeeper.
- All HiveServer2 instances of a particular version, run the following command:
```
hive --service hiveserver2 --deregister <version_number>
```