Ansible 2.4 -> 2.7, include_role and delegate_to

The final solution

Short description of the problem: In Ansible 2.4 it was possible to write something like that:

- include_role:
    name: foo
  delegate_to: foo_host

And it worked as expected: role foo run on host foo_host. Ansible 2.5 has changed that, and include_role ignores delegate_to. (Contrary, import_role, does respect it). I found few clever tricks to live with this, but Alexey Miasoedov pointed out that there is a much neater way, by using an apply parameter for include_role, which supports delegate_to as well as tags and become. I have trouble to find words to express gratitude for that, as it saves me tons of efforts to refactor thousands lines of code.

The final solution

- include_role:
    name: foo
    apply:
      delegate_to: foo_host

(note that apply is offset, as it’s an include_role's parameter).

Compatibility

Unfortunately, there is no way to write a code which works with 2.4 and 2.7 at the same time. apply does not understood in 2.4, so transition should be done in atomic manner.