Purge EC2 Tags that aren't explicitly passed in with Ansible

tagger.yml

# you'll need to have a variable called aws_tags_desired which should be dict with k/v pairs of the tags you want
# also define aws_tags_region
# Note that this is task file, so you'll need to include it or make it the main.yml for a role's tasks directory

- name: Get EC2 Facts
  ec2_metadata_facts:
  register: ec2_facts

- name: Get instance details at the AWS console level
  ec2_instance_facts:
    region: "{{ aws_tags_region }}"
    instance_ids:
      - "{{ ansible_facts['ec2_instance_id'] }}"
  delegate_to: localhost
  register: instance_facts

- name: Set cloudformation tags
  set_fact:
    cf_tags:
      'aws:cloudformation:logical-id': "{{ instance_facts['instances'][0]['tags']['aws:cloudformation:logical-id'] }}" 
      'aws:cloudformation:stack-id': "{{ instance_facts['instances'][0]['tags']['aws:cloudformation:stack-id'] }}" 
      'aws:cloudformation:stack-name': "{{ instance_facts['instances'][0]['tags']['aws:cloudformation:stack-name'] }}" 
  when:
    - instance_facts['instances'][0]['tags']['aws:cloudformation:logical-id'] is defined

- name: Set Desired tags
  set_fact:
    desired_tags: "{{ aws_tags_desired }}"

- name: Add cft tags if needed
  set_fact:
    desired_tags: "{{ desired_tags | combine(cf_tags) }}"
  when: cf_tags is defined

- name: Get list of current tags
  delegate_to: localhost
  become: no
  ec2_tag:
    state: list
    region: "{{ aws_tags_region }}"
    resource: "{{ ec2_facts.ansible_facts.ansible_ec2_instance_id }}"
  register: tag_list

- set_fact:
    tags_to_delete: "{{ tags_to_delete|default({}) | combine({ item.key : item.value }) }}"
  when: "{{ not item.key in desired_tags or desired_tags[item.key] != item.value }}"
  with_dict: "{{ tag_list.tags }}"
  delegate_to: localhost

- name: Remove necessary tags
  delegate_to: localhost
  become: no
  ec2_tag:
    state: absent
    region: "{{ aws_tags_region }}"
    resource: "{{ ec2_facts.ansible_facts.ansible_ec2_instance_id }}"
    tags:  "{{ tags_to_delete }}"
  with_dict: "{{ tags_to_delete }}"
  when: "{{ tags_to_delete is defined }}"

- name: Set instance tags
  become: no
  ec2_tag:
    region: "{{ aws_tags_region }}"
    resource: "{{ ec2_facts.ansible_facts.ansible_ec2_instance_id }}"
    tags: "{{ desired_tags }}"
  delegate_to: localhost