Facts¶

Why This Exists¶

Most plays begin with an implicit setup module run that discovers dozens of details about the host — OS family, IP addresses, memory, mounted disks — before your first real task even starts. Facts are how a playbook adapts to the machine it's actually running against instead of assuming.

What It Will Cover¶

• The implicit Gathering Facts task and gather_facts: false to skip it
• ansible_facts['os_family'], ansible_facts['default_ipv4'], and the rest of the namespaced fact dictionary (vs. the older top-level ansible_* fact variables)
• ansible.builtin.setup run ad hoc, and filter:/gather_subset: to scope what's collected
• Custom facts via /etc/ansible/facts.d/*.fact
• Fact caching (fact_caching = jsonfile/redis) to avoid re-gathering on every run — previewed here, covered in full in Fact Caching

Common Mistakes¶

• Leaving gather_facts: true (the default) on every play, including ones that never reference a fact — real cost at scale, covered in Performance.
• Using the deprecated top-level ansible_distribution style instead of the namespaced ansible_facts['distribution'] form in new playbooks.

Interview Questions¶

• What does gather_facts actually do, and when would you disable it?
• What's the difference between a fact and a registered variable?
• How does fact caching change the cost of repeated runs?

Next¶

Continue to Registered Variables.