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ZooKeeper 3-Node Cluster Installation Guide

Introduction

ZooKeeper is commonly used in distributed systems to manage configuration information, naming services, distributed synchronization, quorum, and state. In addition, distributed systems rely on ZooKeeper to implement consensus, leader election, and group management.

In a production environment, each ZooKeeper node should be run on separate host. This prevents service disruption due to host hardware failure or reboots. This is an important and necessary architectural consideration for building a resilient and highly available distributed system.

Specs

  • 3-node deployment
  • Ubuntu 18.04.3 LTS
  • 4 vCPUs
  • 4 GB RAM
  • 32 GB disk
  • 1 NIC

Prerequisites

Install OpenJDK on all 3 nodes.

sudo apt install openjdk-8-jdk

Installation

Creating Dedicated User for ZooKeeper

sudo useradd zk -m
sudo usermod --shell /bin/bash zk
sudo passwd zk
sudo usermod -aG sudo zk

Configuring SSH Daemon

In /etc/ssh/sshd_config:

PermitRootLogin no
DenyUsers zk

sudo systemctl restart sshd.service

Switch to the zk user for the rest steps.

Creating Data Directory for ZooKeeper

sudo mkdir -p /data/zookeeper
sudo chown zk:zk /data/zookeeper

Downloading and Extracting the ZooKeeper Binaries

cd /opt
sudo wget http://ftp.mirror.tw/pub/apache/zookeeper/zookeeper-3.4.14/zookeeper-3.4.14.tar.gz
sudo tar -zxvf zookeeper-3.4.14.tar.gz
sudo chown zk:zk -R zookeeper-3.4.14
sudo ln -s zookeeper-3.4.14 zookeeper
sudo chown -h zk:zk zookeeper

Configuring ZooKeeper

In /opt/zookeeper/conf/zoo.cfg:

tickTime=2000
dataDir=/data/zookeeper
clientPort=2181
maxClientCnxns=60

Starting ZooKeeper and Testing the Standalone Installation

Start ZooKeeper with the [zkServer.sh](http://zkserver.sh) command.

cd /opt/zookeeper
bin/zkServer.sh start

Connect to the local ZooKeeper server with the following command:

bin/zkCli.sh -server 127.0.0.1:2181

After you’ve done some testing using the client, you will close the client session and shut down the ZooKeeper service.

bin/zkServer.sh stop

Creating and Using a Systemd Unit File

In /etc/systemd/system/zk.service:

[Unit]
Description=ZooKeeper Daemon
Documentation=http://zookeeper.apache.org
Requires=network.target
After=network.target

[Service]
Type=forking
WorkingDirectory=/opt/zookeeper
User=zk
Group=zk
ExecStart=/opt/zookeeper/bin/zkServer.sh start /opt/zookeeper/conf/zoo.cfg
ExecStop=/opt/zookeeper/bin/zkServer.sh stop /opt/zookeeper/conf/zoo.cfg
ExecReload=/opt/zookeeper/bin/zkServer.sh restart /opt/zookeeper/conf/zoo.cfg
TimeoutSec=30
Restart=on-failure

[Install]
WantedBy=default.target

sudo systemctl start zk.service
sudo systemctl enable zk.service

Configuring a Multi-Node ZooKeeper Cluster

In /opt/zookeeper/conf/zoo.cfg, append the following configurations on each of the three nodes:

initLimit=10
syncLimit=5
server.1=zookeeper-1.bampi.net:2888:3888
server.2=zookeeper-2.bampi.net:2888:3888
server.3=zookeeper-3.bampi.net:2888:3888

Create /data/zookeeper/myid with their corresponding IDs, for example zookeeper-1:

1

Running and Testing the Multi-Node Installation

To start a quorum node, first change to the /opt/zookeeper directory on each node:

cd /opt/zookeeper
java -cp zookeeper-3.4.13.jar:lib/log4j-1.2.17.jar:lib/slf4j-log4j12-1.7.25.jar:lib/slf4j-api-1.7.25.jar:conf org.apache.zookeeper.server.quorum.QuorumPeerMain conf/zoo.cfg

Then you can test each node with zkCli.sh.

References