Using ZooKeeper from Scratch

ZooKeeper is an open-source, highly reliable, and distributed consistency coordination service. ZooKeeper is designed to solve the problem that data consistency cannot be ensured for complex and error-prone distributed systems. There is no need to develop dedicated collaborative applications, which is suitable for high availability services to ensure data consistency.

Background Information

Before using the client, you need to download and update the client configuration file on all clients except the client of the active management node.

Procedure

Download the client configuration file.
1. Log in to FusionInsight Manager. For details, see Accessing FusionInsight Manager.
  - Versions earlier than MRS 3.3.0: Choose Cluster > Name of the desired cluster > Dashboard > More > Download Client.
  - MRS 3.3.0 and later: In the upper right corner of the homepage, click More and select Download Client.
2. Download the cluster client.
  Set Select Client Type to Configuration Files Only, select a platform type, and click OK to generate the client configuration file which is then saved in the /tmp/FusionInsight-Client/ directory on the active management node by default.
Log in to the active management node of Manager.
1. Log in to any node where Manager is deployed as user root.
2. Run the following command to identify the active and standby nodes:
  sh ${BIGDATA_HOME}/om-server/om/sbin/status-oms.sh
  
  In the command output, the value of HAActive for the active management node is active, and that for the standby management node is standby. In the following example, node-master1 is the active management node, and node-master2 is the standby management node.
```
HAMode 
double 
NodeName             HostName        HAVersion          StartTime                HAActive             HAAllResOK           HARunPhase  
192-168-0-30         node-master1    V100R001C01        2020-05-01 23:43:02      active               normal               Actived     
192-168-0-24         node-master2    V100R001C01        2020-05-01 07:14:02      standby              normal               Deactived 
```
3. Log in to the primary management node as user root and run the following command to switch to user omm:
  sudo su - omm
Run the following command to switch to the client installation directory, for example, /opt/client:

cd /opt/client
Run the following command to update the client configuration for the active management node.

sh refreshConfig.sh /opt/client Full path of the client configuration file package

For example, run the following command:

sh refreshConfig.sh /opt/client /tmp/FusionInsight-Client/FusionInsight_Cluster_1_Services_Client.tar

If the following information is displayed, the configurations have been updated successfully:
```
ReFresh components client config is complete.
Succeed to refresh components client config.
```

Use the client on a Master node.
1. On the active management node where the client is updated, for example, node 192-168-0-30, run the following command to go to the client directory:
  cd /opt/client
2. Run the following command to configure environment variables:
  source bigdata_env
3. If Kerberos authentication has been enabled for the current cluster, run the following command to authenticate the current user. For details, see Managing Roles to configure roles with required permissions. For details about how to bind roles with users, see Creating a User. If Kerberos authentication is disabled for the current cluster, skip this step:
  kinit MRS cluster user
  
  Example: kinit zookeeperuser.
4. Run the following Zookeeper client command:
  zkCli.sh -server <zookeeper installation node IP>:<port>
  
  Example: zkCli.sh -server node-master1DGhZ:2181
  You can search for clientPort in all ZooKeeper configuration parameters to obtain the value of <port>. The default ports are as follows:
  
  The default open-source port number is 2181.
  
  The default customized port number is 24002.
  Port customization/open source: When creating an LTS version cluster, you can set Component Port to Open source or Custom. If Open source is selected, the open source port is used. If Custom is selected, the customized port is used.
Run the ZooKeeper client command.
1. Create a ZNode.
```
create /test
```
2. View ZNode information.
```
ls /
```
3. Write data to the ZNode.
```
set /test "zookeeper test"
```
4. View the data written to the ZNode.
```
get /test
```
5. Delete the created ZNode.
```
delete /test
```