Instead of hardcoding values in every task, you define variables once and reference them everywhere. Facts go further — Ansible automatically discovers information about each host that you can use without defining anything manually.
Variable Sources
| Source | Scope | Example use |
|---|---|---|
group_vars/all.yml | All hosts | NTP server, DNS |
group_vars/<group>.yml | Hosts in a group | Subnet per VLAN |
host_vars/<host>.yml | Single host | Per-host port |
Playbook vars: | Current play | One-off overrides |
host_vars overrides group_vars, which overrides all. Playbook vars: overrides all of these.
Defining Variables
BASH
homelab-ansible/
├── group_vars/
│ ├── all.yml
│ └── servers.yml
└── host_vars/
└── web01.ymlhomelab-ansible/
├── group_vars/
│ ├── all.yml
│ └── servers.yml
└── host_vars/
└── web01.yml
group_vars/all.yml
ntp_server: "pool.ntp.org"
timezone: "Europe/Amsterdam"ntp_server: "pool.ntp.org"
timezone: "Europe/Amsterdam"
host_vars/web01.yml
http_port: 8080http_port: 8080
Use them in tasks with {{ variable_name }}:
tasks/main.yml
- name: Set timezone
community.general.timezone:
name: "{{ timezone }}"- name: Set timezone
community.general.timezone:
name: "{{ timezone }}"
Ansible Facts
When gather_facts: true (the default), Ansible collects system information from the host at the start of each play.
| Fact | Example value |
|---|---|
ansible_hostname | web01 |
ansible_default_ipv4.address | 192.168.1.10 |
ansible_distribution | Ubuntu |
ansible_os_family | Debian |
ansible_memtotal_mb | 7976 |
To see all available facts for a host:
BASH
ansible web01 -m setupansible web01 -m setup
Using Facts in Tasks
tasks/main.yml
- name: Install packages (Debian)
ansible.builtin.apt:
name: curl
state: present
when: ansible_os_family == "Debian"
- name: Install packages (RedHat)
ansible.builtin.dnf:
name: curl
state: present
when: ansible_os_family == "RedHat"- name: Install packages (Debian)
ansible.builtin.apt:
name: curl
state: present
when: ansible_os_family == "Debian"
- name: Install packages (RedHat)
ansible.builtin.dnf:
name: curl
state: present
when: ansible_os_family == "RedHat"
Registering Task Output
Use register to capture a task result and act on it:
tasks/main.yml
- name: Check if nginx is running
ansible.builtin.systemd:
name: nginx
register: nginx_status
changed_when: false
failed_when: false
- name: Start nginx if not running
ansible.builtin.systemd:
name: nginx
state: started
when: nginx_status.status is defined and nginx_status.status.ActiveState != "active"- name: Check if nginx is running
ansible.builtin.systemd:
name: nginx
register: nginx_status
changed_when: false
failed_when: false
- name: Start nginx if not running
ansible.builtin.systemd:
name: nginx
state: started
when: nginx_status.status is defined and nginx_status.status.ActiveState != "active"
The debug Module
Use debug to inspect variables while developing:
YAML
- name: Show host IP
ansible.builtin.debug:
msg: "Host IP is {{ ansible_default_ipv4.address }}"
- name: Dump all facts
ansible.builtin.debug:
var: ansible_facts- name: Show host IP
ansible.builtin.debug:
msg: "Host IP is {{ ansible_default_ipv4.address }}"
- name: Dump all facts
ansible.builtin.debug:
var: ansible_facts
Recap
You’ve now covered:
- Defining variables in
group_varsandhost_vars - Using gathered facts like
ansible_os_familyfor host-aware tasks - Capturing task output with
register - Inspecting variables with
debug