Open Stack

I proposed a session for the PTG
(https://etherpad.openstack.org/p/tripleo-ptg-queens) about forming a
common plan and vision around Ansible in TripleO.

I think it's important however that we kick this discussion off more
broadly before the PTG, so that we can hopefully have some agreement
for deeper discussions and prototyping when we actually meet in
person.

Right now, we have multiple uses of Ansible in TripleO:

(0) tripleo-quickstart which follows the common and well accepted
approach to bundling a set of Ansible playbooks/roles.

(1) Mistral calling Ansible. This is the approach used by
tripleo-validations where Mistral directly executes ansible playbooks
using a dynamic inventory. The inventory is constructed from the
server related stack outputs of the overcloud stack.

(2) Ansible running playbooks against localhost triggered by the
heat-config Ansible hook. This approach is used by
tripleo-heat-templates for upgrade tasks and various tasks for
deploying containers.

(3) Mistral calling Heat calling Mistral calling Ansible. In this
approach, we have Mistral resources in tripleo-heat-templates that are
created as part of the overcloud stack and in turn, the created
Mistral action executions run ansible. This has been prototyped with
using ceph-ansible to install Ceph as part of the overcloud
deployment, and some of the work has already landed. There are also
proposed WIP patches using this approach to install Kubernetes.

There are also some ideas forming around pulling the Ansible playbooks
and vars out of Heat so that they can be rerun (or run initially)
independently from the Heat SoftwareDeployment delivery mechanism:

(4) https://review.openstack.org/#/c/454816/

(5) Another idea I'd like to prototype is a local tool that runs on
the undercloud and pulls all of the SoftwareDeployment data out of
Heat as the stack is being created and generates corresponding Ansible
playbooks to apply those deployments. Once a given playbook is
generated by the tool, the tool would signal back to Heat that the
deployment is complete. Heat then creates the whole stack without
actually applying a single deployment to an overcloud node. At that
point, Ansible (or Mistral->Ansible for an API) would be used to do
the actual deployment of the Overcloud with the Undercloud as the
ansible runner.

All of this work has merit as we investigate longer term plans, and
it's all at different stages with some being for dev/CI (0), some
being used already in production (1 and 2), some just at the
experimental stage (3 and 4), and some does not exist other than an
idea (5).

My intent with this mail is to start a discussion around what we've
learned from these approaches and start discussing a consolidated plan
around Ansible. And I'm not saying that whatever we come up with
should only use Ansible a certain way. Just that we ought to look at
how users/operators interact with Ansible and TripleO today and try
and come up with the best solution(s) going forward.

I think that (1) has been pretty successful, and my idea with (5)
would use a similar approach once the playbooks were generated.
Further, my idea with (5) would give us a fully backwards compatible
solution with our existing template interfaces from
tripleo-heat-templates. Longer term (or even in parallel for some
time), the generated playbooks could stop being generated (and just
exist in git), and we could consider moving away from Heat more
permanently

I recognize that saying "moving away from Heat" may be quite
controversial. While it's not 100% the same discussion as what we are
doing with Ansible, I think it is a big part of the discussion and if
we want to continue with Heat as the primary orchestration tool in
TripleO.

I've been hearing a lot of feedback from various operators about how
difficult the baremetal deployment is with Heat. While feedback about
Ironic is generally positive, a lot of the negative feedback is around
the Heat->Nova->Ironic interaction. And, if we also move more towards
Ansible for the service deployment, I wonder if there is still a long
term place for Heat at all.

Personally, I'm pretty apprehensive about the approach taken in (3). I
feel that it is a lot of complexity that could be done simpler if we
took a step back and thought more about a longer term approach. I
recognize that it's mostly an experiment/POC at this stage, and I'm
not trying to directly knock down the approach. It's just that when I
start to see more patches (Kubernetes installation) using the same
approach, I figure it's worth discussing more broadly vs trying to
have a discussion by -1'ing patch reviews, etc.

I'm interested in all feedback of course. And I plan to take a shot at
working on the prototype I mentioned in (5) if anyone would like to
collaborate around that.

I think if we can form some broad agreement before the PTG, we have a
chance at making some meaningful progress during Queens.


-- 
-- James Slagle
--