Is it possible to `include` a tasks file with a different set of hosts?

Question

Ideally, I'd like to be able to do something like:

- include: deregister_from_loadbalancer.yml
  delegate_to: loadbalancer

In such a way that I still have access to the vars for the host I'm running the overall play against, but actions are taking place on the loadbalancer host.

Why not separate plays?

I can't just break this into separate plays, because I'm taking machines out of loadbalancer rotation one-at-a-time. Separating into multiple plays would mean something like:

- hosts: loadbalancers
  tasks:
    - include: remove_from_loadbalancer.yml
      vars:
        machine: "{{ item }}"
      with_items: "{{ groups['webservers'] }}"

# at this point in the play I'm being fired for gross incompetence

- hosts: webservers
  tasks:
    # ... update them

- hosts: loadbalancers
  tasks:
    - include: add_to_loadbalancer.yml
      vars:
        machine: "{{ item }}"
      with_items: "{{ groups['webservers'] }}"

Answer 1

If the example you posted...

- include: deregister_from_loadbalancer.yml
  delegate_to: loadbalancer

...does not work, you can still do this. Includes in general can take parameters, so you could write it as:

- include: deregister_from_loadbalancer.yml
  delegate_host: loadbalancer

And in your include deregister_from_loadbalancer.yml you use that var to delegate all your tasks then:

- some: task
  delegate_to: "{{ delegate_host | default(omit) }}"

- another: task
  delegate_to: "{{ delegate_host | default(omit) }}"