Open Stack

I pushed a patch[1] to update our containerized deployment
architecture docs yesterday. There are 2 new fairly useful sections we
can leverage with TripleO's stepwise deployment. They appear to be
used somewhat sparingly so I wanted to get the word out.

The first is 'deploy_steps_tasks' which gives you a means to run
Ansible snippets on each node/role in a stepwise fashion during
deployment. Previously it was only possible to execute puppet or
docker commands where as now that we have deploy_steps_tasks we can
execute ad-hoc ansible in the same manner.

The second is 'external_deploy_tasks' which allows you to use run
Ansible snippets on the Undercloud during stepwise deployment. This is
probably most useful for driving an external installer but might also
help with some complex tasks that need to originate from a single
Ansible client.

The only downside I see to these approaches is that both appear to be
implemented with Ansible's default linear strategy. I saw shardy's
comment here [2] that the :free strategy does not yet apparently work
with the any_errors_fatal option. Perhaps we can reach out to someone
in the Ansible community in this regard to improve running these
things in parallel like TripleO used to work with Heat agents.

This is also how host_prep_tasks is implemented which BTW we should
now get rid of as a duplicate architectural step since we have
deploy_steps_tasks anyway.

[1] https://review.openstack.org/#/c/614822/
[2] http://git.openstack.org/cgit/openstack/tripleo-heat-templates/tree/common/deploy-steps.j2#n554