# Idempotency — Ansible: Automate Servers with Playbooks

Source: https://www.geekswithgeeks.com/en/ansible/pb-idempotency

> Show that running a playbook twice leaves the system unchanged the second time.

## Run it again safely

Idempotency is Ansible's most valuable property: modules check the current state and act only if it differs from what you asked for. That makes playbooks safe to run repeatedly, from CI, on a schedule, or to repair **drift** when someone changed a server by hand. The `command` and `shell` modules are **not** inherently idempotent; use a purpose-built module when one exists, or add `creates:`, `removes:` or `changed_when:` so Ansible can tell whether anything really changed.

## Second run, run for real

I ran the same playbook again. Every task reports ok, the handler does not fire, and the recap shows `changed=0` for both hosts.

```bash
ansible-playbook -i inventory.ini site.yml
```

Output:

```
PLAY RECAP *********************************************************************
web1                       : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
web2                       : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
```

## Prefer modules over shell

`ansible.builtin.apt`, `file`, `copy`, `user`, `service` and many more describe state. `shell: apt install nginx` would report changed every time.

**Quiz:** Why is idempotency valuable?

- [x] Playbooks can be re-run safely and repair drift
- [ ] It makes tasks slower
- [ ] It removes the need for inventory
- [ ] It only works on Windows

*Answer:* Playbooks can be re-run safely and repair drift. Declared state means repeated runs converge to the same result.