I have an inventory with three host groups, something like:

    [all:vars]
    ansible_user = myuser
    ansible_port = 22

    [A]
    XXX.XXX.XXX.XX ansible_ssh_common_args='-o StrictHostKeyChecking=accept-new' 

    [B]
    XXX.XXX.XXX.XX ansible_ssh_common_args='-o StrictHostKeyChecking=accept-new' 

    [C]
    XXX.XXX.XXX.XX ansible_ssh_common_args='-o StrictHostKeyChecking=accept-new'

Each group has a single host.
I have a playlist with multiple task lists, hived off into blocks. I want to run a task list against one host in group A. If that list fails, I want to run a different task list against all the machines in group A and B.

I’m using Ansible v2.16.4.

I thought I might be able to do something like:

- hosts: "[A, B]"
  tags: always
  tasks:
    - name: Execute against A
      block:
        - name: Do something against A
          ansible.builtin.include_tasks:
            file: ./task_lists/a_tasks.yaml
          run_once: true
          delegate_to: "{{ groups['A'][0] }}"

      rescue:
        - name: Do something against A and B
          ansible.builtin.include_tasks:
            file: ./task_lists/ab_tasks.yaml

but this causes my plays to fail. The output seem to show the plays being executed from A onto B, but I’m not entirely sure what [A -> B] means or what it’s doing. As far as I can tell from the docs, I would have assumed the output to have been something like [localhost -> A] for the first bit and then [localhost -> A] [localhost -> B] for the second rescue block.

Does anyone have a better approach?

Thanks