Host and Group Variables¶

• In this lab we master variable management in Ansible - defining variables at host, group, and global levels.
• Understanding variable precedence is critical for writing maintainable playbooks.
• We will practice organizing variables using host_vars/ and group_vars/ directories.

What will we learn?¶

• How to define variables in inventory, host_vars/, and group_vars/
• Ansible’s variable precedence order (22 levels!)
• How to use special variables and magic variables
• Best practices for organizing variables

Prerequisites¶

• Complete the Lab 002 in order to have a working Ansible controller and inventory configuration.
• Complete Lab 005 to understand how Ansible gathers host information.

01. Where to Define Variables¶

Ansible has many places to define variables. From lowest to highest priority:

TIP: Higher number = higher priority. Extra vars (-e) always win.

02. Inline Inventory Variables¶

# inventory (INI format)
[webservers]
linux-server-1 http_port=80 document_root=/var/www/html
linux-server-2 http_port=8080 document_root=/srv/www

[dbservers]
linux-server-3 db_port=5432

[all:vars]
ansible_user=root
env=production

03. group_vars/ Directory¶

# Directory structure
group_vars/
├── all.yml          # Applies to every host
├── webservers.yml   # Applies to [webservers] group only
└── dbservers.yml    # Applies to [dbservers] group only

# group_vars/all.yml
---
ansible_user: root
ansible_python_interpreter: /usr/bin/python3
ntp_server: pool.ntp.org
timezone: UTC


# group_vars/webservers.yml
---
http_port: 80
https_port: 443
document_root: /var/www/html
nginx_worker_processes: auto
max_upload_size: 100M


# group_vars/dbservers.yml
---
db_port: 5432
db_name: appdb
db_user: appuser
backup_enabled: true
backup_retention_days: 30

04. host_vars/ Directory¶

# Directory structure
host_vars/
├── linux-server-1.yml   # Only for linux-server-1
├── linux-server-2.yml   # Only for linux-server-2
└── linux-server-3.yml   # Only for linux-server-3

# host_vars/linux-server-1.yml
---
server_role: primary-web
http_port: 80
ssl_enabled: true
server_alias: web-primary


# host_vars/linux-server-3.yml
---
server_role: primary-db
db_port: 5432
db_max_connections: 200

05. Magic Variables¶

Ansible provides built-in variables automatically:

# Using magic variables in a task
- name: Show host information
  ansible.builtin.debug:
    msg: |
      Host: {{ inventory_hostname }}
      IP: {{ ansible_default_ipv4.address }}
      OS: {{ ansible_distribution }} {{ ansible_distribution_version }}
      Groups: {{ group_names | join(', ') }}

06. Hands-on¶

1. Create the group_vars/ and host_vars/ directory structure inside the controller, create group_vars/all.yml with ansible_user, env, and ntp_server keys, and create group_vars/webservers.yml with http_port and document_root.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && mkdir -p group_vars host_vars"
docker exec ansible-controller sh -c "cd /labs-scripts && cat > group_vars/all.yml << 'EOF'
---
ansible_user: root
ansible_python_interpreter: /usr/bin/python3
env: lab
ntp_server: pool.ntp.org
EOF"
docker exec ansible-controller sh -c "cd /labs-scripts && cat > group_vars/webservers.yml << 'EOF'
---
http_port: 80
document_root: /var/www/html
EOF"

1. Create host_vars/linux-server-1.yml that overrides http_port to 8080 and sets a server_alias variable.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && cat > host_vars/linux-server-1.yml << 'EOF'
---
server_alias: primary-web
http_port: 8080
EOF"

1. Write a playbook debug_vars.yml that prints inventory_hostname, group_names, http_port (with a default of N/A), and ansible_distribution for every host, then run it.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && cat > debug_vars.yml << 'EOF'
---
- name: Show variables
  hosts: all
  gather_facts: true
  tasks:
    - name: Display host-specific variables
      ansible.builtin.debug:
        msg:
          - \"Host: {{ inventory_hostname }}\"
          - \"Groups: {{ group_names }}\"
          - \"HTTP Port: {{ http_port | default('N/A') }}\"
          - \"OS: {{ ansible_distribution }}\"
EOF"
docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook debug_vars.yml"

1. Override the env variable at runtime to production without editing any file.

??? success “Solution”

docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook debug_vars.yml -e 'env=production'"

1. Use an ad-hoc command with the debug module (or setup) to confirm that linux-server-1 has a different http_port value than the other servers.

??? success “Solution”

# Run the playbook and observe the HTTP Port line differs for linux-server-1
docker exec ansible-controller sh -c "cd /labs-scripts && ansible-playbook debug_vars.yml"

### Output (relevant lines)
# linux-server-1 → HTTP Port: 8080  (from host_vars override)
# linux-server-2 → HTTP Port: 80    (from group_vars/webservers.yml)

07. Summary¶

• Variables have 15+ levels of precedence; extra vars (-e) always win
• Use group_vars/ for group-wide settings and host_vars/ for host-specific overrides
• Magic variables (inventory_hostname, ansible_distribution) are auto-populated by Ansible
• The hostvars dictionary lets you access any host’s variables from any task
• Inline inventory variables are convenient but group_vars/ and host_vars/ files scale better