Using ansible local facts to make your playbooks more declarative

Sometimes you need to declaratively manage packages on your target system but absense of state in ansible makes it inconvinient

For example you want a certain variable/list to represent a set of installed packages on your system, but when you remove package from the list it still is present on your target machine

Here is the simple pattern based on ansible_local facts that i found on the internet that may help you

Basically it holds state information in a file /etc/ansible/facts.d/*.fact on your target machine in a json/ini format and to reference it u can use {{ ansible_local.* }}

In this example we manage package creation but you can adapt it to yout own needs like maybe managing ssh authorized_keys file, etc.

- name: Defining packages to install
  set_fact:
    packages_to_install:
      - curl
      - git
      - vim

- name: Installing a bunch of packages
  apt:
    name: "{{ packages_to_install }}"
    state: present

- name: Checking if state has changed
  apt:
    name: "{{ item }}"
    state: absent
  loop: "{{ ansible_local.packages | default(packages_to_install) | difference(packages_to_install) }}"
  register: removed_packages

- name: Ensuring that facts.d directory exists
  file:
    state: directory
    path: /etc/ansible/facts.d
    recurse: true
    owner: root
    mode: "0644"

- name: Adding current state to packages.fact
  copy:
    content: "{{ packages_to_install | to_json }}"
    dest: /etc/ansible/facts.d/packages.fact
    owner: root
    mode: "0644"
  when: removed_packages.changed

References

1. Discovering variables: facts and magic variables # adding custom facts - https://docs.ansible.com/projects/ansible/latest/playbook_guide/playbooks_vars_facts.html#adding-custom-facts