Playbooks, Modules & Handlers

Inventory & a Basic Playbook

# inventory.ini
[webservers]
web1.example.com
web2.example.com

[dbservers]
db1.example.com

# site.yml
- hosts: webservers
  become: true       # escalate privileges (sudo) for this play
  tasks:
    - name: Install nginx
      apt:               # dedicated module — idempotent by design
        name: nginx
        state: present

    - name: Deploy config
      template:
        src: nginx.conf.j2   # Jinja2 template
        dest: /etc/nginx/nginx.conf
      notify: restart nginx  # only fires the handler if this task actually changed something

  handlers:
    - name: restart nginx
      service:
        name: nginx
        state: restarted

ansible-playbook -i inventory.ini site.yml
ansible-playbook -i inventory.ini site.yml --check   # dry run — see what WOULD change

Why Idempotency Matters

# BAD — shell/command are NOT idempotent by default; Ansible has no way
# to know if this actually changed anything, so it ALWAYS reports "changed",
# and any handler notified by it fires on every single run
- name: Install nginx (wrong way)
  shell: apt-get install -y nginx

# GOOD — the apt module checks current state first, only reports
# "changed" when a real change happened
- name: Install nginx (correct)
  apt:
    name: nginx
    state: present