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)

1. Role defaults (defaults/main.yml)
2. Inventory group_vars
3. Inventory host_vars
4. Playbook vars
5. Role vars (vars/main.yml)
6. Task vars
7. 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