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Sounds like an important discussion to have with the operators in Denver. Should put this on the schedule for the Ops meetup.

--Rocky

> -----Original Message-----
> From: Matt Riedemann [mailto:mriedemos at gmail.com]
> Sent: Thursday, September 06, 2018 1:59 PM
> To: OpenStack Development Mailing List (not for usage questions)
> <openstack-dev at lists.openstack.org>; openstack-
> operators at lists.openstack.org
> Subject: [openstack-dev] [nova][placement][upgrade][qa] Some upgrade-
> specific news on extraction
> 
> I wanted to recap some upgrade-specific stuff from today outside of the
> other [1] technical extraction thread.
> 
> Chris has a change up for review [2] which prompted the discussion.
> 
> That change makes placement only work with placement.conf, not
> nova.conf, but does get a passing tempest run in the devstack patch [3].
> 
> The main issue here is upgrades. If you think of this like deprecating config
> options, the old config options continue to work for a release and then are
> dropped after a full release (or 3 months across boundaries for CDers) [4].
> Given that, Chris's patch would break the standard deprecation policy. Clearly
> one simple way outside of code to make that work is just copy and rename
> nova.conf to placement.conf and voila. But that depends on *all*
> deployment/config tooling to get that right out of the gate.
> 
> The other obvious thing is the database. The placement repo code as-is
> today still has the check for whether or not it should use the placement
> database but falls back to using the nova_api database [5]. So technically you
> could point the extracted placement at the same nova_api database and it
> should work. However, at some point deployers will clearly need to copy the
> placement-related tables out of the nova_api DB to a new placement DB and
> make sure the 'migrate_version' table is dropped so that placement DB
> schema versions can reset to 1.
> 
> With respect to grenade and making this work in our own upgrade CI testing,
> we have I think two options (which might not be mutually
> exclusive):
> 
> 1. Make placement support using nova.conf if placement.conf isn't found for
> Stein with lots of big warnings that it's going away in T. Then Rocky nova.conf
> with the nova_api database configuration just continues to work for
> placement in Stein. I don't think we then have any grenade changes to make,
> at least in Stein for upgrading *from* Rocky. Assuming fresh devstack installs
> in Stein use placement.conf and a placement-specific database, then
> upgrades from Stein to T should also be OK with respect to grenade, but
> likely punts the cut-over issue for all other deployment projects (because we
> don't CI with grenade doing
> Rocky->Stein->T, or FFU in other words).
> 
> 2. If placement doesn't support nova.conf in Stein, then grenade will require
> an (exceptional) [6] from-rocky upgrade script which will (a) write out
> placement.conf fresh and (b) run a DB migration script, likely housed in the
> placement repo, to create the placement database and copy the placement-
> specific tables out of the nova_api database. Any script like this is likely
> needed regardless of what we do in grenade because deployers will need to
> eventually do this once placement would drop support for using nova.conf (if
> we went with option 1).
> 
> That's my attempt at a summary. It's going to be very important that
> operators and deployment project contributors weigh in here if they have
> strong preferences either way, and note that we can likely do both options
> above - grenade could do the fresh cutover from rocky to stein but we allow
> running with nova.conf and nova_api DB in placement in stein with plans to
> drop that support in T.
> 
> [1]
> http://lists.openstack.org/pipermail/openstack-dev/2018-
> September/subject.html#134184
> [2] https://review.openstack.org/#/c/600157/
> [3] https://review.openstack.org/#/c/600162/
> [4]
> https://governance.openstack.org/tc/reference/tags/assert_follows-
> standard-deprecation.html#requirements
> [5]
> https://github.com/openstack/placement/blob/fb7c1909/placement/db_api
> .py#L27
> [6] https://docs.openstack.org/grenade/latest/readme.html#theory-of-
> upgrade
> 
> --
> 
> Thanks,
> 
> Matt
> 
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