Playbooks, Plays, and Tasks¶

What You'll Learn¶

• The three-level structure: playbook → play(s) → task(s)
• The keywords that decide what runs, on which hosts, in what order
• How this scales past a single flat task list

Mental Model¶

flowchart TD
    P[Playbook: site.yml] --> Play1[Play: Configure web servers]
    P --> Play2[Play: Configure db servers]
    Play1 --> T1[Task: Install nginx]
    Play1 --> T2[Task: Deploy config]
    Play1 --> T3[Task: Start service]
    Play2 --> T4[Task: Install postgresql]
    Play2 --> T5[Task: Initialize database]

• A playbook is a YAML file containing one or more plays.
• A play maps a group of hosts to a set of tasks (and optionally roles) — it's the unit that has its own hosts:, become:, and vars:.
• A task calls exactly one module with specific arguments.

Minimal Example¶

---
- name: Configure web servers
  hosts: web
  become: true
  tasks:
    - name: Install nginx
      ansible.builtin.package:
        name: nginx
        state: present

Practical Example — Multiple Plays, Ordering Keywords¶

---
- name: Preflight checks on every host
  hosts: all
  tasks:
    - name: Ensure disk space is sufficient
      ansible.builtin.command: df -h /
      register: disk_check
      changed_when: false

- name: Configure web servers
  hosts: web
  become: true
  pre_tasks:
    - name: Update package cache
      ansible.builtin.package:
        update_cache: true
  roles:
    - nginx
  post_tasks:
    - name: Confirm nginx responds
      ansible.builtin.uri:
        url: "http://localhost"
        status_code: 200

- name: Configure database servers
  hosts: db
  become: true
  roles:
    - postgresql

• pre_tasks / post_tasks run before/after roles:, regardless of what's inside the role — useful for "always check X before this role runs" logic that shouldn't live inside the role itself.
• Plays run in order, top to bottom, each against its own hosts: pattern.
• Within a play, by default (the linear strategy), Ansible runs each task on all targeted hosts before moving to the next task — not host-by-host sequentially. See Forks, Serial, Strategy.

Key Play-Level Keywords¶

Common Mistakes¶

• Assuming tasks run host-by-host from top to bottom — the default is task-by-task, across the whole batch of hosts, which surprises people used to imperative scripting.
• Putting everything in one giant play instead of splitting by host group and responsibility.
• Setting gather_facts: true (the default) on plays that never use facts — wasted time on every run at scale. See Performance.

Interview Questions¶

• What's the difference between a playbook, a play, and a task?
• What do pre_tasks and post_tasks let you do that tasks alone can't?
• Does Ansible run task-by-task or host-by-host by default?

Next¶

Continue to Modules — the thing every task actually calls.