[qa][openstack-ansible] redefining devstack

Mohammed Naser mnaser at vexxhost.com
Sat Jun 1 12:35:14 UTC 2019

Hi everyone,

This is something that I've discussed with a few people over time and
I think I'd probably want to bring it up by now.  I'd like to propose
and ask if it makes sense to perhaps replace devstack entirely with
openstack-ansible.  I think I have quite a few compelling reasons to
do this that I'd like to outline, as well as why I *feel* (and I could
be biased here, so call me out!) that OSA is the best option in terms
of a 'replacement'

# Why not another deployment project?
I actually thought about this part too and considered this mainly for
ease of use for a *developer*.

At this point, Puppet-OpenStack pretty much only deploys packages
(which means that it has no build infrastructure, a developer can't
just get $commit checked out and deployed).

TripleO uses Kolla containers AFAIK and those have to be pre-built
beforehand, also, I feel they are much harder to use as a developer
because if you want to make quick edits and restart services, you have
to enter a container and make the edit there and somehow restart the
service without the container going back to it's original state.
Kolla-Ansible and the other combinations also suffer from the same

OpenStack Ansible is unique in the way that it pretty much just builds
a virtualenv and installs packages inside of it.  The services are
deployed as systemd units.  This is very much similar to the current
state of devstack at the moment (minus the virtualenv part, afaik).
It makes it pretty straight forward to go and edit code if you
need/have to.  We also have support for Debian, CentOS, Ubuntu and
SUSE.  This allows "devstack 2.0" to have far more coverage and make
it much more easy to deploy on a wider variety of operating systems.
It also has the ability to use commits checked out from Zuul so all
the fancy Depends-On stuff we use works.

# Why do we care about this, I like my bash scripts!
As someone who's been around for a *really* long time in OpenStack,
I've seen a whole lot of really weird issues surface from the usage of
DevStack to do CI gating.  For example, one of the recent things is
the fact it relies on installing package-shipped noVNC, where as the
'master' noVNC has actually changed behavior a few months back and it
is completely incompatible at this point (it's just a ticking thing
until we realize we're entirely broken).

To this day, I still see people who want to POC something up with
OpenStack or *ACTUALLY* try to run OpenStack with DevStack.  No matter
how many warnings we'll put up, they'll always try to do it.  With
this way, at least they'll have something that has the shape of an
actual real deployment.  In addition, it would be *good* in the
overall scheme of things for a deployment system to test against,
because this would make sure things don't break in both ways.

Also: we run Zuul for our CI which supports Ansible natively, this can
remove one layer of indirection (Zuul to run Bash) and have Zuul run
the playbooks directly from the executor.

# So how could we do this?
The OpenStack Ansible project is made of many roles that are all
composable, therefore, you can think of it as a combination of both
Puppet-OpenStack and TripleO (back then).  Puppet-OpenStack contained
the base modules (i.e. puppet-nova, etc) and TripleO was the
integration of all of it in a distribution.  OSA is currently both,
but it also includes both Ansible roles and playbooks.

In order to make sure we maintain as much of backwards compatibility
as possible, we can simply run a small script which does a mapping of
devstack => OSA variables to make sure that the service is shipped
with all the necessary features as per local.conf.

So the new process could be:

1) parse local.conf and generate Ansible variables files
2) install Ansible (if not running in gate)
3) run playbooks using variable generated in #1

The neat thing is after all of this, devstack just becomes a thin
wrapper around Ansible roles.  I also think it brings a lot of hands
together, involving both the QA team and OSA team together, which I
believe that pooling our resources will greatly help in being able to
get more done and avoiding duplicating our efforts.

# Conclusion
This is a start of a very open ended discussion, I'm sure there is a
lot of details involved here in the implementation that will surface,
but I think it could be a good step overall in simplifying our CI and
adding more coverage for real potential deployers.  It will help two
teams unite together and have more resources for something (that
essentially is somewhat of duplicated effort at the moment).

I will try to pick up sometime to POC a simple service being deployed
by an OSA role instead of Bash, placement which seems like a very
simple one and share that eventually.

Thoughts? :)

Mohammed Naser — vexxhost
D. 514-316-8872
D. 800-910-1726 ext. 200
E. mnaser at vexxhost.com
W. http://vexxhost.com

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