Local cachíng of Ansible Facts
Every time Ansible runs a Playbook, the first step (by default) is gathering facts about the target system:
PLAY [all-systems] TASK [Gathering Facts] ok: [host1] ok: [host2]
This step is implicit, and it is not necessary (but possible) to add the gather facts step to every Playbook. The module which retrieves all the information is "setup", and by default it tries to gather as much information about the target system as possible. When the "setup" task is added as an extra step in the Playbook, the information about the destination system is refreshed and updated:
tasks: - name: Refresh destination information setup:
That might be necessary when a Playbook changed vital system settings.
Gathering the facts is a time-consuming process, and for a short Playbook it is quite possible that this is the longest-running task. And it's repeated every time the Playbook runs.
Ansible provides Cache plugins which can store the gathered facts. If the system facts don't change between Playbook runs, this will greatly speed up the runtime of Playbooks. The facts cache can be stored in JSON files, in a Redis DB, in a Memcache, and a few other options. The simplest way, without additional tools required, is the "jsonfile" cache. Central implementations like Redis or Memcache allow multiple Ansible controller hosts to use the same facts cache, whereas local caches like "JSON" are only available on a single host, and every Ansible controller must build and maintain it's own cache.
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