Ansible Playbook Development
Overview
Ansible playbooks declare desired system state rather than imperative commands. The core principle is idempotency: running a playbook multiple times produces the same result without unintended changes.
When to Use
- Creating new playbooks or roles
- Writing inventory files
- Debugging YAML syntax errors
- Troubleshooting module parameter issues
- Understanding variable precedence
- Converting shell scripts to Ansible
Quick Reference
Project Structure
project/
├── ansible.cfg # Configuration
├── inventory # Host definitions
├── group_vars/ # Group variables
├── host_vars/ # Host-specific vars
├── roles/ # Reusable roles
└── playbooks/ # Playbook files
Essential ansible.cfg
[defaults]
inventory = ./inventory
roles_path = ./roles
host_key_checking = False
stdout_callback = yaml
[privilege_escalation]
become = True
become_method = sudo
Module Patterns
| Operation | Module | Key Parameters |
|---|
| Create directory | ansible.builtin.file | state: directory, mode, owner |
| Copy file | ansible.builtin.copy | src, dest, mode |
| Template | ansible.builtin.template | src, dest, variables in .j2 |
| Install package | ansible.builtin.package | name, state: present |
| Manage service | ansible.builtin.service | name, state, enabled |
| Run command | ansible.builtin.command | cmd, register result, set changed_when |
Variable Precedence (lowest to highest)
- Role defaults (
defaults/main.yml) - Inventory group_vars
- Inventory host_vars
- Playbook vars
- Role vars (
vars/main.yml) - Task vars
- Extra vars (
-e)
Handlers
tasks:
- name: Update config
ansible.builtin.template:
src: app.conf.j2
dest: /etc/app.conf
notify: Restart app
handlers:
- name: Restart app
ansible.builtin.service:
name: app
state: restarted
Error Handling
- block:
- name: Risky operation
ansible.builtin.command: /opt/app/upgrade.sh
rescue:
- name: Handle failure
ansible.builtin.debug:
msg: "Upgrade failed, rolling back"
always:
- name: Cleanup
ansible.builtin.file:
path: /tmp/upgrade.lock
state: absent
Common Mistakes
| Mistake | Fix |
|---|
| Using short module names | Always use FQCN: ansible.builtin.copy not copy |
| Hardcoded values | Extract to variables in defaults/main.yml |
Missing changed_when on commands | Add changed_when: "'created' in result.stdout" |
| Forgetting handler flush | Use meta: flush_handlers when needed before dependent tasks |
| YAML indentation errors | Use 2 spaces, never tabs |
| Colon in unquoted string | Quote values containing : |
Verification Commands
ansible-playbook --syntax-check playbook.yml # Check YAML
ansible-playbook --check playbook.yml # Dry run
ansible-playbook --check --diff playbook.yml # Show file changes
ansible-inventory --list # Verify inventory
ansible-inventory --host hostname # Check host vars
