Playbook Variables¶

In this lab we explore how to define, pass, and use variables in Ansible playbooks.
Variables make playbooks reusable across different environments and hosts.
We will cover inline vars, variable files, register, set_fact, and Jinja2 filters.

What will we learn?¶

Defining variables inline, in files, and from the command line
Using vars_files to load variable files
Accessing variables with Jinja2 {{ variable }} syntax
Using register to capture task output and set_fact to create derived variables

Prerequisites¶

Complete Lab 004 to understand how playbooks are structured.

01. Defining Variables¶

In the Playbook (Inline)¶

---
- name: Inline variables example
  hosts: all
  vars:
    app_name: myapp
    app_port: 8080
    app_user: deploy
    app_packages:
      - nginx
      - curl
      - git
    app_config:
      max_connections: 100
      timeout: 30

  tasks:
    - name: Print app name
      ansible.builtin.debug:
        msg: "App: {{ app_name }} running on port {{ app_port }}"

    - name: Access list variable
      ansible.builtin.debug:
        msg: "Packages to install: {{ app_packages | join(', ') }}"

    - name: Access dictionary variable
      ansible.builtin.debug:
        msg: "Max connections: {{ app_config.max_connections }}"

In Separate Variable Files¶

# vars/main.yml
---
app_name: myapp
app_port: 8080
app_user: deploy
db_host: localhost
db_port: 5432
db_name: production_db

# Reference in playbook
---
- name: Load variables from file
  hosts: all
  vars_files:
    - vars/main.yml
    - vars/secrets.yml # Can load multiple files

  tasks:
    - name: Show app name
      ansible.builtin.debug:
        var: app_name

02. Variable Types and Syntax¶

---
- name: Variable types
  hosts: localhost
  vars:
    # String
    greeting: "Hello, World!"

    # Integer
    max_retries: 3

    # Boolean
    debug_mode: true

    # List
    servers:
      - web1
      - web2
      - web3

    # Dictionary
    database:
      host: localhost
      port: 5432
      name: mydb

    # Multiline string
    config_file: |
      [server]
      host = localhost
      port = 8080

  tasks:
    - name: Use string
      ansible.builtin.debug:
        msg: "{{ greeting }}"

    - name: Use list item
      ansible.builtin.debug:
        msg: "First server: {{ servers[0] }}"

    - name: Use dict value (dot notation)
      ansible.builtin.debug:
        msg: "DB host: {{ database.host }}"

    - name: Use dict value (bracket notation)
      ansible.builtin.debug:
        msg: "DB port: {{ database['port'] }}"

03. Command-Line Variables¶

# Pass a single variable
ansible-playbook site.yml -e "env=production"

# Pass multiple variables
ansible-playbook site.yml -e "env=production app_port=443"

# Pass a YAML/JSON string
ansible-playbook site.yml -e '{"env": "production", "app_port": 443}'

# Pass from a file (prefix with @)
ansible-playbook site.yml -e "@vars/production.yml"

04. `register` - Capture Task Output¶

---
- name: Capture command output
  hosts: all

  tasks:
    - name: Get disk usage
      ansible.builtin.command:
        cmd: df -h /
      register: disk_usage

    - name: Show disk usage
      ansible.builtin.debug:
        var: disk_usage.stdout

    - name: Show return code
      ansible.builtin.debug:
        msg: "Return code: {{ disk_usage.rc }}"

    - name: Show all registered data
      ansible.builtin.debug:
        var: disk_usage

Common `register` attributes¶

Attribute	Description
`stdout`	Standard output as a string
`stderr`	Standard error as a string
`stdout_lines`	Standard output as a list of lines
`rc`	Return code (0 = success)
`changed`	Whether the task made a change
`failed`	Whether the task failed

05. `set_fact` - Create Variables During Play¶

---
- name: Create facts dynamically
  hosts: all
  gather_facts: true

  tasks:
    - name: Set a fact based on OS
      ansible.builtin.set_fact:
        package_manager: "{{ 'apt' if ansible_os_family == 'Debian' else 'yum' }}"

    - name: Calculate a derived value
      ansible.builtin.set_fact:
        app_url: "http://{{ ansible_default_ipv4.address }}:{{ app_port | default(80) }}"

    - name: Show derived facts
      ansible.builtin.debug:
        msg:
          - "Package manager: {{ package_manager }}"
          - "App URL: {{ app_url }}"

06. `vars_prompt` - Interactive Variables¶

---
- name: Interactive variable input
  hosts: all
  vars_prompt:
    - name: app_env
      prompt: "Which environment? (dev/staging/prod)"
      default: dev
      private: false

    - name: db_password
      prompt: "Database password"
      private: true # Hides input (like a password field)

  tasks:
    - name: Show environment
      ansible.builtin.debug:
        msg: "Deploying to: {{ app_env }}"

07. Variable Filters¶

---
- name: Variable filters
  hosts: localhost
  vars:
    my_list: [3, 1, 4, 1, 5, 9, 2, 6]
    my_string: "  hello world  "
    my_path: /etc/nginx/nginx.conf

  tasks:
    - name: String filters
      ansible.builtin.debug:
        msg:
          - "Upper: {{ my_string | upper }}"
          - "Trimmed: {{ my_string | trim }}"
          - "Length: {{ my_string | length }}"
          - "Replace: {{ my_string | replace('world', 'ansible') }}"

    - name: List filters
      ansible.builtin.debug:
        msg:
          - "Sorted: {{ my_list | sort }}"
          - "Unique: {{ my_list | unique }}"
          - "Min: {{ my_list | min }}"
          - "Max: {{ my_list | max }}"
          - "Joined: {{ my_list | join(', ') }}"

    - name: Default filter
      ansible.builtin.debug:
        msg: "Port: {{ undefined_var | default(8080) }}"

    - name: Basename filter
      ansible.builtin.debug:
        msg: "Filename: {{ my_path | basename }}"

Practice

08. Hands-on¶

Create a vars/ directory inside the controller and write a vars/lab014.yml file containing a greeting string, a lab_number integer, a packages list, and a server_config dictionary with port and max_connections keys.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && mkdir -p vars"
docker exec ansible-controller sh -c "cd /labs-scripts && cat > vars/lab014.yml << 'EOF'
---
greeting: \"Welcome to Ansible Labs!\"
lab_number: 14
packages:
  - curl
  - vim
  - git
server_config:
  port: 8080
  max_connections: 50
  debug: false
EOF"

Write a playbook lab014-variables.yml that loads vars/lab014.yml via vars_files, prints the greeting, the package list joined by commas, and the server port.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && cat > lab014-variables.yml << 'EOF'
---
- name: Variables Practice
  hosts: all
  gather_facts: true
  vars_files:
    - vars/lab014.yml
  vars:
    inline_var: \"I was defined inline\"

  tasks:
    - name: Show the greeting
      ansible.builtin.debug:
        msg: \"{{ greeting }}\"

    - name: Show lab number
      ansible.builtin.debug:
        msg: \"Lab {{ lab_number }}\"

    - name: Show package list
      ansible.builtin.debug:
        msg: \"Packages: {{ packages | join(', ') }}\"

    - name: Show server config
      ansible.builtin.debug:
        msg:
          - \"Port: {{ server_config.port }}\"
          - \"Max connections: {{ server_config.max_connections }}\"
EOF"

Add a task that runs hostname and registers the output, then prints it with debug.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && cat >> lab014-variables.yml << 'EOF'

    - name: Get hostname
      ansible.builtin.command:
        cmd: hostname
      register: hostname_output

    - name: Show registered hostname
      ansible.builtin.debug:
        msg: \"Hostname: {{ hostname_output.stdout }}\"
EOF"

Run the playbook, then re-run it overriding greeting from the command line.

??? success “Solution”

# Normal run
docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook lab014-variables.yml"

# Override greeting at runtime
docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook lab014-variables.yml -e \"greeting='Override greeting!'\""

Add a set_fact task that builds a server_url variable combining ansible_default_ipv4.address and server_config.port, then print it.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && cat >> lab014-variables.yml << 'EOF'

    - name: Create derived fact
      ansible.builtin.set_fact:
        server_url: \"http://{{ ansible_default_ipv4.address }}:{{ server_config.port }}\"

    - name: Show server URL
      ansible.builtin.debug:
        msg: \"Server URL: {{ server_url }}\"
EOF"
docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook lab014-variables.yml"

09. Summary¶

Variables can be defined inline (vars:), in files (vars_files:), or from the command line (-e)
Use {{ variable }} Jinja2 syntax to reference variables in any string value
register captures task output; access it with .stdout, .rc, .changed, .stdout_lines
set_fact creates new variables mid-play that persist for the rest of the play
Filters like | default(), | upper, | join() transform variable values inline
Extra vars (-e) always override any other variable definition

Playbook Variables¶

What will we learn?¶

Prerequisites¶

01. Defining Variables¶

In the Playbook (Inline)¶

In Separate Variable Files¶

02. Variable Types and Syntax¶

03. Command-Line Variables¶

04. register - Capture Task Output¶

Common register attributes¶

05. set_fact - Create Variables During Play¶

06. vars_prompt - Interactive Variables¶

07. Variable Filters¶

08. Hands-on¶

09. Summary¶

04. `register` - Capture Task Output¶

Common `register` attributes¶

05. `set_fact` - Create Variables During Play¶

06. `vars_prompt` - Interactive Variables¶