Are package facts getting invalidated automatically when I install remove packages?

Question

In Ansible I can use a task such as:

- name: Gather the package facts
  package_facts:
    manager: auto

to gather the package facts and a condition such as:

when: "'foobar' in ansible_facts.packages"

to only execute a task when package foobar is installed. Gathering the package facts is a rather lengthy process compared to many of the other tasks in my playbooks.

For the sake of this question we can also assume that instead of manager: auto I'm using manager: apt.

Now I was unable to find any information regarding if or when the fact ansible_facts.packages gets invalidated after a subsequent package manager operation and a look at the fact via debug module doesn't give me any indication as to when it was gathered. Similarly I found no obvious way of checking against the cache time of the package manager. So in essence I was unable to come up with a means of only gathering (or re-gathering) the package facts when necessary.

So, questions:

1. does the ansible_facts.packages fact get invalidated after subsequent package manager operations?
2. if not: how can I get close to the desired "only gather package facts if something changed"?

NB: according to ansible --version I am running version 2.10.7.

Answer 1

Package facts (as any other facts like devices, disks and their partitions, IP addresses...) don't refresh automagically.

In your case, you can use a handler and notify it from any task that can possibly invalidate the cache. Here is a quickNdirty example:

- name: Pseudo code demo for package facts refresh
  hosts: localhost
  
  tasks:

    - name: Gather the package facts unconditionally at play start
      package_facts:

    - name: Make sure package X is installed
      package:
        name: package_X
      notify: refresh_package_facts
    
    # By default, handlers run at the end of the play.
    # If you want to force them to run at a certain point,
    # you need the following meta task.
    # Note => this will run !!ALL!! notified handlers
    - name: Run handlers if notified
      meta: flush_handlers

    - name: This task will run with an up-to-date cache
      debug:
        msg: "{{ ansible_facts.packages | length }} packages are installed"

  handlers:

    - name: Refresh the package facts
      package_facts:
      listen: refresh_package_facts