Open Stack

On Wednesday at the PTG, TripleO held a session around our current use
of Ansible and how to move forward. I'll summarize the results of the
session. Feel free to add anything I forgot and provide any feedback
or questions.

We discussed the existing uses of Ansible in TripleO and how they
differ in terms of what they do and how they interact with Ansible. I
covered this in a previous email[1], so I'll skip over summarizing
those points again.

I explained a bit about the  "openstack overcloud config download"
approach implemented in Pike by the upgrades squad. This method
no-op's out the deployment steps during the actual Heat stack-update,
then uses the cli to query stack outputs to create actual Ansible
playbooks from those output values. The Undercloud is then used as the
Ansible runner to apply the playbooks to each Overcloud node.

I created a sequence diagram for this method and explained how it
would also work for initial stack deployment[2]:

https://slagle.fedorapeople.org/tripleo-ansible-arch.png

The high level proposal was to move in a direction where we'd use the
config download method for all Heat driven stack operations
(stack-create and stack-update).

We highlighted and discussed several key points about the method shown
in the diagram:

- The entire sequence and flow is driven via Mistral on the Undercloud
by default. This preserves the API layer and provides a clean reusable
interface for the CLI and GUI.

- It would still be possible to run ansible-playbook directly for
various use cases (dev/test/POC/demos). This preserves the quick
iteration via Ansible that is often desired.

- The remaining SoftwareDeployment resources in tripleo-heat-templates
need to be supported by config download so that the entire
configuration can be driven with Ansible, not just the deployment
steps. The success criteria for this point would be to illustrate
using an image that does not contain a running os-collect-config.

- The ceph-ansible implementation done in Pike could be reworked to
use this model. "config download" could generate playbooks that have
hooks for calling external playbooks, or those hooks could be
represented in the templates directly. The result would be the same
either way though in that Heat would no longer be triggering a
separate Mistral workflow just for ceph-ansible.

- We will need some centralized log storage for the ansible-playbook
results and should consider using ARA.

As it would be a lot of work to eventually make this method the
default, I don't expect or plan that we will complete all this work in
Queens. We can however start moving in this direction.

Specifically, I hope to soon add support to config download for the
rest of the SoftwareDeployment resources in tripleo-heat-templates as
that will greatly simplify the undercloud container installer. Doing
so will illustrate using the ephemeral heat-all process as simply a
means for generating ansible playbooks.

I plan to create blueprints this week for Queens and beyond. If you're
interested in this work, please let me know. I'm open to the idea of
creating an official squad for this work, but I'm not sure if it's
needed or not.

As not everyone was able to attend the PTG, please do provide feedback
about this plan as it should still be considered open for discussion.

[1] http://lists.openstack.org/pipermail/openstack-dev/2017-July/119405.html
[2] https://slagle.fedorapeople.org/tripleo-ansible-arch.png

-- 
-- James Slagle
--