Fact Caching¶

Why This Exists¶

Fact gathering is a real remote execution step (the implicit setup module call) with real cost, repeated at the start of nearly every play — fact caching lets a run reuse facts gathered recently instead of re-gathering them every single time.

What It Will Cover¶

[defaults]
fact_caching = jsonfile
fact_caching_connection = /tmp/ansible_fact_cache
fact_caching_timeout = 86400

• Backends: jsonfile (local disk, simplest), redis/memcached (shared across multiple control nodes or CI runners)
• fact_caching_timeout — how long a cached fact is trusted before re-gathering
• gather_facts: smart — gather only if the cache doesn't already have fresh facts for this host
• set_fact ... cacheable: true — persisting a computed value into the fact cache, not just the current run
• The tradeoff: stale cached facts (a host's IP changed, cache didn't expire yet) vs. gathering cost — when each backend makes sense

Common Mistakes¶

• Enabling fact caching with a long timeout on hosts whose facts genuinely change often (autoscaled infrastructure), then debugging "wrong" values that are actually just stale.
• Using jsonfile caching across multiple CI runners that don't share a filesystem — each runner gets its own cache, defeating the point.

Interview Questions¶

• What problem does fact caching solve, and what's the tradeoff against always gathering fresh?
• Why would a team choose redis fact caching over jsonfile?

Next¶

Continue to Connection Plugins.