Master Ansible: Automate Docker Installation on CentOS with Playbooks

Ansible Overview

Ansible is a Python‑written automation tool that enables cluster management and common operations tasks.

Many companies deploy services on clusters ranging from a few virtual machines to thousands; Ansible can perform batch operations across such clusters.

Automation platform based on Ansible scripts

Jenkins‑style CI/CD automation platform

SDK‑based Python automation platform

Docker containers with orchestration

This article shares experience using Ansible to automatically install Docker and Docker‑Compose.

1. Install Ansible

The control node must have Python 2. Windows cannot be used as a control node; supported OS include Red Hat, Debian, CentOS, macOS, BSD, etc.

Install via pip

sudo pip install ansible

Install via system package manager

CentOS (yum): sudo yum install ansible Ubuntu (apt):

sudo apt-get install software-properties-common
sudo apt-add-repository ppa:ansible/ansible
sudo apt-get update
sudo apt-get install ansible

2. Basic Ansible Usage

Using ansible-playbook

An ansible‑playbook (playbook) combines a series of automation tasks in a defined order and logic, making task management easier.

Typical command to run a playbook:

ansible-playbook docker.yml -i hosts -u alex -k -K

This command specifies the remote user and prompts for the SSH and sudo passwords.

To view module documentation:

# List all modules
ansible-doc -l
# Show usage of the yum module
ansible-doc yum

Playbook Directory Structure

├── group_vars        ← common variables for all hosts
│   └── all
├── hosts             ← inventory file
├── roles             ← reusable roles (e.g., etcd, initial, loop)
│   ├── etcd
│   │   ├── files
│   │   │   └── etcd-proxy.service
│   │   ├── handlers
│   │   │   └── main.yml
│   │   ├── tasks
│   │   │   ├── config.yml
│   │   │   ├── main.yml
│   │   │   ├── package.yml
│   │   │   └── service.yml
│   │   └── templates
│   │       └── etcd-proxy.conf
│   ├── initial
│   │   ├── files
│   │   │   ├── hosts
│   │   │   ├── resolv.conf
│   │   │   └── updatedb.conf
│   │   ├── handlers
│   │   ├── tasks
│   │   │   ├── main.yml
│   │   │   ├── mlocate.yml
│   │   │   ├── package.yml
│   │   │   ├── sysctl.yml
│   │   │   └── yumrepo.yml
│   │   └── templates
│   │       ├── centos7.repo
│   │       └── docker.repo
│   └── loop
│       ├── files
│       ├── handlers
│       ├── tasks
│       │   ├── main.yml
│       │   └── t1.yml
│       └── templates
└── site.yml          ← main entry playbook

3. Ansible Install Docker

The playbook checks whether Docker is available, installs Docker, adds the user to the Docker group, and installs pip and Docker‑Compose.

Prefer Built‑in Modules

When a built‑in module can accomplish a task, use it instead of raw shell commands.

# Using shell to install a package
- name: install yum-utils
  shell: yum install yum-utils

# Using the yum module
- name: install yum-utils
  yum:
    name: yum-utils
    state: present

# Using pip module to install docker‑compose
- name: install docker-compose
  pip:
    name: docker-compose
    extra_args: "-i {{ pip.index_url }} --trusted-host {{ pip.trusted_host }}"

Using register and when

register

stores a task's result in a variable; when evaluates that variable to conditionally run subsequent tasks.

- name: check docker
  shell: docker -v
  register: result
  ignore_errors: true

- name: include install tasks if docker not present
  include_tasks: install.yml
  when: result is failed

Execution results are shown in the following screenshots: