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What is the difference between a variable and a fact?

Infrastructure as Code (Terraform, Ansible) · Intermediate level

Answer

A variable is a value you define or pass into Ansible. A fact is information discovered from a managed host, such as OS family, IP addresses, CPU count, memory, and distribution version. Facts are gathered at runtime and can drive conditional logic.

Technical explanation

Facts are host-derived and can change over time.

Variables can come from inventory, roles, playbooks, command line, or registered results.

Caching facts can speed large runs but requires freshness awareness.

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: What is the difference between a variable and a fact?

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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• What does terraform init do?
• What is the Terraform state file, and why is it critical?
• Why should state be stored remotely, and what backend would you use on AWS?
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