Conditionals¶

What You'll Learn¶

• How when: decides whether a task runs
• Common conditional patterns using facts and registered results
• How when: interacts with loops

Minimal Example¶

- name: Install nginx only on Debian-family hosts
  ansible.builtin.package:
    name: nginx
    state: present
  when: ansible_facts['os_family'] == "Debian"

when: is evaluated per host, fresh, every time the task is reached — not computed once for the whole play.

Practical Example — Gating on a Registered Result¶

- name: Check if the app is already deployed
  ansible.builtin.stat:
    path: /opt/app/current
  register: app_check

- name: Deploy the app
  ansible.builtin.copy:
    src: app.tar.gz
    dest: /opt/app/current
  when: not app_check.stat.exists

register captures a task's result; a later when: reads it. This is the standard pattern for "only do this if that other thing hasn't already happened."

Combining Conditions¶

when:
  - ansible_facts['os_family'] == "Debian"
  - ansible_facts['distribution_major_version'] | int >= 20

A YAML list under when: is an implicit AND. For OR, use Jinja2's or directly:

when: ansible_facts['distribution'] == "Ubuntu" or ansible_facts['distribution'] == "Debian"

when: With loop¶

- name: Only install packages that are Debian-specific
  ansible.builtin.package:
    name: "{{ item }}"
    state: present
  loop:
    - nginx
    - ufw
  when: ansible_facts['os_family'] == "Debian"

The condition is re-evaluated for every item, not once for the whole loop.

Common Mistakes¶

• Wrapping the condition in {{ }} — when: is already Jinja2-evaluated; when: "{{ x == 1 }}" works but is redundant and non-idiomatic. Write when: x == 1.
• Forgetting a when: on a loop is checked per item, leading to surprise when only some items run.
• Gating a privilege-escalated (become: true) task on a condition that's wrong — a bad when: can skip a needed security control just as easily as skip a harmless one. Treat conditional logic on sensitive tasks with the same review rigor as the task itself.

Interview Questions¶

• Is when: evaluated once per play or once per host per task?
• How do you express AND vs. OR in a when: condition?
• How does when: interact with loop?

Next¶

Continue to Loops.