[Feature Request] rolling-upgrade of a marathon HA cluster with the leading-marathon last

[lhoss]

Motivation:

Do the upgrade with the minimum (1) leader fail-overs (vs worst-case: 'number of HA master/marathon nodes'), as recommended on:
https://mesosphere.github.io/marathon/docs/upgrade/index.html
http://stackoverflow.com/questions/33042343/is-it-possible-to-perform-a-zero-downtime-upgrade-or-reconfiguration-of-mesos

Current State

Currently I've a flexible serial attribute to provide the (optional) rolling upgrade logic, in a typical
playbook:

- hosts: marathon
  become: True
  roles:
    - {role: teralytics.marathon}
  environment: "{{proxy_env}}"
  tags: marathon
  serial: "{{ (rolling_upgrade|default(false)|bool)|ternary(1,0) }}"

Goal

run the upgrade in a specific order, so that the current leader (can be provided for ex. using a consul-DNS or mesos-dns url like 'leader.mesos' ) is deployed last.

I've some ideas, but before doing actual work, wanted to ask the ansible/devOps community for any existing solutions or recommendations.
I see 2 diff approaches:

• (a) Splitting the playbook into 2 diff runs:
• 1.run on the list of all selected-nodes, excluding the leader.mesos (could be done with some list mangling, including the resolution of dns entries to IPs to match the leader.mesos with the actual hostname (from the inventory)! )
• 2.run on the remaining leader.mesos host
• (b): using a dynamic inventory, resp. extra python logic that returns a single list of hosts in the right order

Ideas!?