Configure and Start Apache ZooKeeper
| ![[Tip]](../common/images/admon/tip.png) | Tip | 
|---|---|
| If you are running a highly available HDFS cluster, configure and restart Apache ZooKeeper before you upgrade HDFS. This best practice lets the upgraded ZKFC work with your primary NameNode and your Standby NameNode. | 
- Replace your configuration after upgrading on all the ZooKeeper nodes. Replace the ZooKeeper template configuration in - /etc/zookeeper/conf.
- Start ZooKeeper. - On all ZooKeeper server host machines, run the following command to start ZooKeeper and the ZKFC: - su - zookeeper -c "/usr/hdp/current/zookeeper-server/bin/zookeeper-server start" 

