Apache ZooKeeper

Ansible role for installing and configuring Apache ZooKeeper

This role can be used to install and cluster multiple ZooKeeper nodes, this uses all hosts defined for the "zookeeper-nodes" group in the inventory file by default. All servers are added to the zoo.cfg file along with the leader and election ports. Firewall ports could be opened after setting true to zookeeper_firewalld variable

Supported Platforms

• Debian 10.x
• RedHat 7
• RedHat 8
• Ubuntu 18.04.x
• Ubuntu 20.04.x

Requirements

Java: Java 8 / 11

Ansible 2.9.16 or 2.10.4 are the minimum required versions to workaround an issue with certain kernels that have broken the systemd status check. The error message "Service is in unknown state" will be output when attempting to start the service via the Ansible role and the task will fail. The service will start as expected if the systemctl start command is run on the physical host. See ansible/ansible#71528 for more information.

Role Variables

Variable	Default	Comment
zookeeper_mirror	https://dlcdn.apache.org/zookeeper
zookeeper_version	3.9.3
zookeeper_package	apache-zookeeper-{{ zookeeper_version }}-bin.tar.gz
zookeeper_group	zookeeper
zookeeper_user	zookeeper
zookeeper_root_dir	/usr/share
zookeeper_install_dir	'{{ zookeeper_root_dir}}/apache-zookeeper-{{zookeeper_version}}'
zookeeper_dir	'{{ zookeeper_root_dir }}/zookeeper'
zookeeper_log_dir	/var/log/zookeeper
zookeeper_data_dir	/var/lib/zookeeper
zookeeper_data_log_dir	/var/lib/zookeeper
zookeeper_client_port	2181
zookeeper_id	1	Unique per server and should be declared in the inventory file
zookeeper_leader_port	2888
zookeeper_election_port	3888
zookeeper_servers	zookeeper-nodes	See below
zookeeper_servers_use_inventory_hostname	false	See below
zookeeper_environment	"JVMFLAGS": "-javaagent:/opt/jolokia/jolokia-jvm-1.6.0-agent.jar"
zookeeper_config_params		A key-value dictionary that will be templated into zoo.cfg
zookeeper_firewalld	false

Inventory and zookeeper_servers variable

zookeeper_servers variable above accepts a list of inventory hostnames. These will be used in the zoo.cfg to configure a multi-server cluster so the hosts can find each other. By default, the hostname used in the zoo.cfg will be the hostname reported by the hostname command on the server(provided by the ansible_nodename variable). See the example below.

Assuming the below inventory file, and that the hostname command returns only the hostname and does not include the domain name.

[zookeeper-nodes]
zoo1.foo.com zookeeper_id=1       #hostname command returns "zoo1"
zoo2.foo.com zookeeper_id=2       #hostname command returns "zoo2"
zoo3.foo.com zookeeper_id=3       #hostname command returns "zoo3"

And assuming the following role variables:

---
- role: sleighzy.zookeeper
  zookeeper_servers:
    - zoo1.foo.com
    - zoo2.foo.com
    - zoo3.foo.com

The templated zoo.cfg file will contain the below entries:

server.1=zoo1:2888:3888
server.2=zoo2:2888:3888
server.3=zoo3:2888:3888

If you DO NOT want this behaviour and would like the zoo.cfg to template the inventory_hostname then set zookeeper_servers_use_inventory_hostname to true

Default Ports

Port	Description
2181	Client connection port
2888	Quorum port for clustering
3888	Leader election port for clustering

Default Directories and Files

Description	Directory / File
Installation directory	/usr/share/apache-zookeeper-<version>
Symlink to install directory	/usr/share/zookeeper
Symlink to configuration	/etc/zookeeper/zoo.cfg
Log files	/var/log/zookeeper
Data directory for snapshots and myid file	/var/lib/zookeeper
Data directory for transaction log files	/var/lib/zookeeper
Systemd service	/usr/lib/systemd/system/zookeeper.service
System Defaults	/etc/default/zookeeper

Starting and Stopping ZooKeeper services

• The ZooKeeper service can be started via: systemctl start zookeeper
• The ZooKeeper service can be stopped via: systemctl stop zookeeper

Four Letter Word Commands

ZooKeeper can use commands based on four letter words, see https://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_4lw

The below example uses the stat command to find out which instance is the leader :

for i in 1 2 3 ; do
  echo "zookeeper0$i is a "$(echo stat | nc zookeeper0$i 2181 | grep ^Mode | awk '{print $2}');
done

Dependencies

No dependencies

Example Playbook

- hosts: zookeeper-nodes
  roles:
    - sleighzy.zookeeper

Linting

Linting should be done using ansible-lint

pip3 install ansible-lint --user

ansible-lint -c ./.ansible-lint .

Testing

This module uses the Ansible Molecule testing framework. This test suite creates a ZooKeeper cluster consisting of three nodes running within Docker containers. Each container runs a different OS to test the supported platforms for this Ansible role.

As per the [Molecule Installation guide] this should be done using a virtual environment. The commands below will create a Python virtual environment and install Molecule including the Docker driver.

$ python3 -m venv molecule-venv
$ source molecule-venv/bin/activate
(molecule-venv) $ pip3 install ansible docker "molecule-plugins[docker]"

Run playbook and tests. Linting errors need to be corrected before Molecule will execute any tests. This will run all tests and then destroy the Docker containers.

molecule test

The below command can be used to run the playbook without the tests. This can be run multiple times when making changes to the role, and ensuring that operations are idempotent.

molecule converge

The below commands can be used to just run the tests without tearing everything down. The command molecule verify can be repeated for each test run.

molecule create
molecule converge
molecule verify

Tear down Molecule tests and Docker containers.

molecule destroy

License