Interview › Infrastructure as Code (Terraform, Ansible)
How does Ansible gather facts, and how do you use them in conditionals?
Infrastructure as Code (Terraform, Ansible) · Intermediate level
Answer
Ansible gathers facts with the setup module at the start of a play when gather_facts is true. Those facts are available under ansible_facts and commonly used in when clauses to branch by OS family, distribution version, network interface, or hardware capability.
Technical explanation
gather_facts can be disabled for speed when facts are not needed.
Fact names help write portable tasks such as ansible_facts['os_family'] == 'RedHat'.
For custom facts, use local facts or set_fact carefully.
Prefer idempotent modules over shell so repeated runs are safe and change reporting is meaningful.
Separate reusable role logic from inventory-specific variables so the same automation works across environments.
Run lint, syntax checks, check mode where useful, and staged rollouts before production-wide changes.
Hands-on example
1. Model variables and facts for: How does Ansible gather facts, and how do you use them in conditionals?
2. Create inventory variables:
group_vars/web.yml:
app_port: 8080
package_name_by_os:
RedHat: httpd
Debian: apache2
host_vars/web1.yml:
app_port: 9090
3. Use facts and variables in a task:
- name: Install OS-specific web package
ansible.builtin.package:
name: "{{ package_name_by_os[ansible_facts['os_family']] }}"
state: present
when: ansible_facts['os_family'] in package_name_by_os
4. Run ansible-playbook site.yml -e app_port=7070 in a lab to see extra vars override lower-precedence values.
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