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Apache Zookeeper - creating Server Ensemble Using Docker Desktop

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Thirumurthi S
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Table of contents

  • In this post we will run three Zookeeper Server Ensemble using Docker and connect using Docker zkcli client.

Pre-requisites:

  • Docker desktop installed

Create Configuration for each Zookeeper server

  1. Create the zookeeper configuration for three Zookeeper server.

    • Note: This configuration usually can be updated as zk.conf file, check the documentation in here we will use the configuration file as environment variable to the docker container.

    • Create a folder named zookeeper

    • Save the below content in zk1.env file, similarly we do the same for other servers as well.

  2. Below is configuration for zookeeper1 server

    • Note: the ZOO_SERVERS key value should be in single line sperated by space for each server.
ZOO_TICK_TIME=3000
ZOO_INIT_LIMIT=5
ZOO_SYNC_LIMIT=2
ZOO_MY_ID=1
ZOO_STANDALONE_ENABLED=true
ZOO_ADMINSERVER_ENABLED=true
ZOO_SERVERS=server.1=zookeeper1:2888:3888;2181 server.2=zookeeper2:2888:3888;2181 server.3=zookeeper3:2888:3888;2181
  • Below is configuration for Zookeeper2 server save as zk2.env, ZOO_MY_ID=2
ZOO_TICK_TIME=3000
ZOO_INIT_LIMIT=5
ZOO_SYNC_LIMIT=2
ZOO_MY_ID=2
ZOO_STANDALONE_ENABLED=true
ZOO_ADMINSERVER_ENABLED=true
ZOO_SERVERS=server.1=zookeeper1:2888:3888;2181 server.2=zookeeper2:2888:3888;2181 server.3=zookeeper3:2888:3888;2181
  • Below is configuration for Zookeeper2 server save as zk3.env, ZOO_MY_ID=3
ZOO_TICK_TIME=3000
ZOO_INIT_LIMIT=5
ZOO_SYNC_LIMIT=2
ZOO_MY_ID=2
ZOO_STANDALONE_ENABLED=true
ZOO_ADMINSERVER_ENABLED=true
ZOO_SERVERS=server.1=zookeeper1:2888:3888;2181 server.2=zookeeper2:2888:3888;2181 server.3=zookeeper3:2888:3888;2181

Create docker bridge network for each Zookeeper to connect

  1. Create a docker bridge network for each of the Server to connect
$ docker network create --driver bridge zk-cluster

## use below command to list the bridge network we created

$ docker network ls

Run Zookeeper container exposing ports

  1. Using the docker run command we will start three Zookeeper ensemble server

    • Below are the command to run the zookeeper image and expose the ports so host can connect to it.

    • Port usage

      • 2181 - Client connection port
      • 2888 - is used by the leader node to communicate with follower node called Quorum port
      • 8080 - Admin server port, we can access the state of the node using API
      • 3888 - Leader election port (to vote a leader)

      Note: We only need to expose two port 2181 and 8080 since other ports are used by the Zookeeper Ensemble

# navigate to the zookeeper folder in gitbash terminal

# running container in detached mode and removing once stopped 
# passing the environment file along with created network 
# we are using the image zookeeper from the docker hub

docker run -d --rm -p 2181:2181 -p 8880:8080 --env-file zk1.env --name zookeeper1 --network zk-cluster zookeeper:latest

docker run -d --rm -p 2182:2181 -p 8881:8080 --env-file zk2.env --name zookeeper2 --network zk-cluster zookeeper:latest

docker run -d --rm -p 2183:2181 -p 8882:8080 --env-file zk3.env --name zookeeper3 --network zk-cluster  zookeeper:latest

Validate the Zookeeper services are running

  • Running the above command will start the Zookeeper ensemble, we can validate using docker ps command.
$ docker ps
CONTAINER ID   IMAGE              COMMAND                  CREATED          STATUS          PORTS                                                                NAMES
d54accf53541   zookeeper:latest   "/docker-entrypoint.…"   9 seconds ago    Up 7 seconds    2888/tcp, 3888/tcp, 0.0.0.0:2183->2181/tcp, 0.0.0.0:8882->8080/tcp   zookeeper3
b09e008a0e94   zookeeper:latest   "/docker-entrypoint.…"   24 seconds ago   Up 22 seconds   2888/tcp, 3888/tcp, 0.0.0.0:2182->2181/tcp, 0.0.0.0:8881->8080/tcp   zookeeper2
c561495d7d49   zookeeper:latest   "/docker-entrypoint.…"   39 seconds ago   Up 36 seconds   2888/tcp, 0.0.0.0:2181->2181/tcp, 3888/tcp, 0.0.0.0:8880->8080/tcp   zookeeper1

Use Docker Zookeeper zkCli.sh to connect to the server ensemble

  • Connect using Docker Zookeeper client (zkCli.sh) to the above ensemble
    • we are using the container name as host and corresponding client port to connect
$ docker run -it --rm --network zk-cluster --link zookeeper1:zookeeper1 zookeeper zkCli.sh -server "zookeeper1:2181,zookeeper2:2181,zookeeper3:2181"
  • Snapshot of client connecting to the servers

image

Check for the leader info

Access the admin API from host to check the leader amongst the server ensemble

  • Use http://localhost:8880/commands/leader to check which is the leader node, output should be something like below
   {
    is_leader: false,
    leader_id: 2,
    leader_ip: "zookeeper2",
    command: "leader",
    error: null
    }
  • Zookeeper2 url http:///loclahost:8881/commands/leader current this one is elected as leader
  {
    is_leader: true,
    leader_id: 2,
    leader_ip: "zookeeper2",
    command: "leader",
    error: null
    }
  • Zookeeper3 url http://localhost:8882/commands/leader
   {
      is_leader: false,
      leader_id: 2,
      leader_ip: "zookeeper2",
      command: "leader",
      error: null
      }

Notes:

  • The above is not production ready, in case we need to persist the data, logs, etc. for which we need to mount volumes.
  • We can create the volumes for data and logs using docker volume and attach during docker run command

  • Sample command of how to create volume and attach to run command

    $ docker volume create --driver local --opt type=none --opt device=/c/thiru/zookeeper/data/zk1 --opt o=bind --name zk1-dataDir

$ docker run -d --rm -p 2182:2181 --publish 8880:8080 --env-file zk1.env --mount source=zk12-dataDir,target=/data --mount source=zk1-logs,target=/logs 
--name zookeeper2 --network zk-cluster zookeeper:latest

Reference:

zookeeperDocker