Ansible Variables — Define, Use, and Override Vars

---
- name: Deploy application
  hosts: webservers
  vars:
    app_name: myapp
    app_port: 8080
    app_env: production
    app_user: deploy
  tasks:
    - name: Show config
      ansible.builtin.debug:
        msg: "Deploying {{ app_name }} on port {{ app_port }}"

# vars/production.yml
app_name: myapp
app_port: 8080
app_env: production
db_host: db.internal
db_port: 5432
db_name: myapp_prod

# playbook.yml
---
- hosts: webservers
  vars_files:
    - vars/production.yml
  tasks:
    - debug:
        msg: "DB: {{ db_host }}:{{ db_port }}/{{ db_name }}"

project/
├── inventory/
│   ├── production
│   ├── group_vars/
│   │   ├── all.yml           ← All hosts
│   │   ├── webservers.yml    ← Web server group
│   │   └── dbservers.yml     ← DB server group
│   └── host_vars/
│       ├── web-01.yml        ← Specific host
│       └── db-01.yml

# group_vars/all.yml — applies to all hosts
ntp_server: time.google.com
dns_servers:
  - 8.8.8.8
  - 8.8.4.4

# group_vars/webservers.yml
nginx_worker_processes: 4
app_port: 8080

# host_vars/web-01.yml
nginx_worker_processes: 8    # Override for this specific host

# Extra vars (highest precedence!)
ansible-playbook site.yml -e "app_version=2.1.0 app_env=staging"

# JSON format
ansible-playbook site.yml -e '{"app_version": "2.1.0", "debug_mode": true}'

# From a file
ansible-playbook site.yml -e @vars/deploy.yml

- name: Set variable at runtime
  ansible.builtin.set_fact:
    app_url: "https://{{ app_domain }}:{{ app_port }}"
    total_memory_gb: "{{ ansible_memtotal_mb / 1024 | round(1) }}"

- name: Get current version
  ansible.builtin.command: /opt/app/version
  register: version_result

- debug:
    msg: "Current version: {{ version_result.stdout }}"

# In task parameters
- ansible.builtin.template:
    src: "{{ app_name }}.conf.j2"
    dest: "/etc/{{ app_name }}/config.conf"
    owner: "{{ app_user }}"

# In conditions
- ansible.builtin.service:
    name: nginx
    state: started
  when: install_nginx | default(true)

# In loops
- ansible.builtin.user:
    name: "{{ item.name }}"
    groups: "{{ item.groups }}"
  loop: "{{ users }}"

# In templates (Jinja2)
# server {
#     listen {{ app_port }};
#     server_name {{ app_domain }};
#     root {{ app_root }};
# }

# String
app_name: myapp
app_name: "my app"        # Quotes for special chars

# Number
app_port: 8080
timeout: 30.5

# Boolean
debug_mode: true
ssl_enabled: false

# List
packages:
  - nginx
  - redis
  - postgresql
# Or inline: packages: [nginx, redis, postgresql]

# Dictionary
database:
  host: db.internal
  port: 5432
  name: myapp
  credentials:
    user: admin
    password: "{{ vault_db_password }}"

# Access dict values
# {{ database.host }}
# {{ database['port'] }}
# {{ database.credentials.user }}

# Use default filter to prevent undefined errors
- debug:
    msg: "Port: {{ app_port | default(8080) }}"

# Default for boolean
- service:
    name: nginx
    state: started
  when: install_nginx | default(true)

# Default empty list
- user:
    name: "{{ item }}"
  loop: "{{ extra_users | default([]) }}"

# Default empty string
- debug:
    msg: "Prefix: {{ prefix | default('') }}"

# Type conversion
port: "{{ input_port | int }}"
enabled: "{{ input_flag | bool }}"
items: "{{ input_csv | split(',') }}"

# String manipulation
lower: "{{ name | lower }}"
upper: "{{ name | upper }}"
replaced: "{{ path | replace('old', 'new') }}"
trimmed: "{{ input | trim }}"

# List operations
first: "{{ servers | first }}"
last: "{{ servers | last }}"
count: "{{ servers | length }}"
joined: "{{ servers | join(',') }}"
unique: "{{ tags | unique }}"
sorted: "{{ names | sort }}"

# Dict operations
keys: "{{ config | dict2items }}"
merged: "{{ defaults | combine(overrides) }}"

# Math
rounded: "{{ value | round(2) }}"
absolute: "{{ number | abs }}"
max_val: "{{ [10, 20, 5] | max }}"

group_vars/
├── all.yml              # Shared defaults
├── production.yml       # Production overrides
└── staging.yml          # Staging overrides

# group_vars/all.yml
app_port: 8080
log_level: info
replicas: 1

# group_vars/production.yml
log_level: warn
replicas: 3
ssl_enabled: true

# group_vars/staging.yml
log_level: debug
replicas: 1
ssl_enabled: false

vars:
  # OS-specific package names
  nginx_package: "{{ 'nginx' if ansible_os_family == 'Debian' else 'nginx' }}"
  php_package: "{{ 'php-fpm' if ansible_os_family == 'Debian' else 'php-fpm' }}"
  
  # Environment-based settings
  worker_count: "{{ ansible_processor_vcpus * 2 }}"
  cache_size: "{{ (ansible_memtotal_mb * 0.25) | int }}m"

# group_vars/production/vault.yml (encrypted)
vault_db_password: supersecret
vault_api_key: abc123

# group_vars/production/vars.yml (references vault)
db_password: "{{ vault_db_password }}"
api_key: "{{ vault_api_key }}"

# Encrypt
ansible-vault encrypt group_vars/production/vault.yml

# Run with vault
ansible-playbook site.yml --ask-vault-pass

# Check if defined before using
- debug:
    msg: "{{ my_var }}"
  when: my_var is defined

# Or use default
- debug:
    msg: "{{ my_var | default('fallback') }}"

# Debug: show where a variable comes from
ansible -m debug -a "var=hostvars[inventory_hostname]" web-01

# YAML auto-types: 8080 is an int, "8080" is a string
port: 8080       # int
port: "8080"     # string

# Force type with filters
- debug:
    msg: "{{ port | int + 1 }}"