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

For MRS 2.x or earlier, perform the following operations:

Download the client configuration file.
1. Log in to the MRS console. In the left navigation pane, choose Clusters > Active Clusters, and click the cluster to be operated.
2. Click the Components tab.
3. Click Download Client.
  Set Client Type to Only configuration files, Download Path to Server, and click OK to generate the client configuration file. The generated file is saved in the /tmp/MRS-client directory on the active management node by default.
  
  Figure 1 Downloading only the client configuration files
Log in to the active management node of MRS Manager.
1. On the MRS console, choose Clusters > Active Clusters and click a cluster name. On the Nodes tab, view the node names. The node whose name contains master1 is the Master1 node, and the node whose name contains master2 is the Master2 node.
  The active and standby management nodes of MRS Manager are installed on Master nodes by default. Because Master1 and Master2 are switched over in active and standby mode, Master1 is not always the active management node of MRS Manager. Run a command in Master1 to check whether Master1 is active management node of MRS Manager. For details about the command, see 2.d.
2. Log in to the Master1 node using the password as user root.
3. Run the following commands to switch to user omm:
  sudo su - root
  
  su - omm
4. Run the following command to check the active management node of MRS Manager:
  sh ${BIGDATA_HOME}/om-0.0.1/sbin/status-oms.sh
  
  In the command output, the node whose HAActive is active is the active management node, and the node whose HAActive is standby is the standby management node. In the following example, mgtomsdat-sh-3-01-1 is the active management node, and mgtomsdat-sh-3-01-2 is the standby management node.
```
Ha mode
double
NodeName              HostName                      HAVersion          StartTime                HAActive             HAAllResOK           HARunPhase 
192-168-0-30          mgtomsdat-sh-3-01-1           V100R001C01        2014-11-18 23:43:02      active               normal               Actived    
192-168-0-24          mgtomsdat-sh-3-01-2           V100R001C01        2014-11-21 07:14:02      standby              normal               Deactived
```
5. Log in to the active management node, for example, 192-168-0-30 of MRS Manager 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/MRS-client/MRS_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.
```
You can also refer to method 2 in Updating a Client (Versions Earlier Than 3.x) to perform operations in 1 to 4.
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 is enabled for the current cluster, run the following command to authenticate the current 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
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
```

For MRS 3.x or later, perform the following operations:

Download the client configuration file.
1. Log in to FusionInsight Manager. For details, see Accessing FusionInsight Manager (MRS 3.x or Later).
2. Choose Cluster > Name of the desired cluster > Dashboard > More > Download Client.
3. 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.. 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
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
```