zookeeper server ensemble

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

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.
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

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

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

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:

Apache Zookeeper - creating Server Ensemble Using Docker Desktop

Table of contents

Create Configuration for each Zookeeper server

Create docker bridge network for each Zookeeper to connect

Run Zookeeper container exposing ports

Validate the Zookeeper services are running

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

Check for the leader info