Ansible for sysadmins - the modern CM tool

Ansible is the most common configuration management tool for sysadmins. It is agentless (uses SSH), declarative (YAML), and has a large module ecosystem.

Install Ansible

# Debian/Ubuntu
sudo apt install ansible

# RHEL family
sudo dnf install ansible-core

# Or via pip
pip install ansible

Configure inventory

/etc/ansible/hosts:

[webservers]
web01.example.com
web02.example.com
web03.example.com

[databases]
db01.example.com

[production:children]
webservers
databases

Or in YAML:

all:
  children:
    webservers:
      hosts:
        web01.example.com:
        web02.example.com:
        web03.example.com:
    databases:
      hosts:
        db01.example.com:

First playbook

# ping.yml
- name: Ping all hosts
  hosts: all
  tasks:
    - name: Ping
      ansible.builtin.ping:

Run:

ansible-playbook -i inventory ping.yml

Modules

Modules are the building blocks. Common ones:

# Package
- apt:
    name: nginx
    state: present
  become: yes

# Service
- service:
    name: nginx
    state: started
    enabled: yes
  become: yes

# File
- copy:
    src: files/nginx.conf
    dest: /etc/nginx/nginx.conf
    owner: root
    group: root
    mode: '0644'
  become: yes

# User
- user:
    name: deploy
    state: present
    shell: /bin/bash
  become: yes

# Command (only when no module exists)
- command: /usr/bin/foo --bar
  become: yes

Variables and templates

- hosts: webservers
  vars:
    nginx_worker_processes: 4
    nginx_listen_port: 80
  tasks:
    - template:
        src: nginx.conf.j2
        dest: /etc/nginx/nginx.conf
      become: yes

nginx.conf.j2:

worker_processes {{ nginx_worker_processes }};
listen {{ nginx_listen_port }};

Handlers

Run only on change:

- name: Configure nginx
  template:
    src: nginx.conf.j2
    dest: /etc/nginx/nginx.conf
  become: yes
  notify: reload nginx

handlers:
  - name: reload nginx
    service:
      name: nginx
      state: reloaded
    become: yes

Handlers run at the end of the playbook, only if a task notified them.

Roles

Organise playbooks:

roles/
  nginx/
    tasks/main.yml
    handlers/main.yml
    templates/nginx.conf.j2
    files/index.html
  postgresql/
    tasks/main.yml

Use:

- hosts: webservers
  roles:
    - nginx

Knowledge check