[atomic-devel] Changing hosted ostree repo so that we align "released content" with 2wk releases

[Dusty Mabe <dusty dustymabe com>]

Note: please don't respond to this email. Please continue discussion
      in the linked ticket.

This is a partial implementation of releng ticket 6545 [1] which is a
migration of the old releng trac ticket 6313 [2].

Gross simplification: In the ticket two things were requested:

- The ostree commits should have slower cadence
- Version numbers of the pungi run match the ostree commits

I have got together with colin (some time ago) and patrick (recently)
to discuss an implementation for the first bulleted ask: "ostree
commits should have slower cadence". This proposal is for that work
item.

Currently what we have is ostree composes that run as part of (or
immediately after) bodhi runs that push out new updated rpms into the
updates or updates-testing yum repos in Fedora. As part of this a new
ostree commit is created with the new content and the 
fedora-atomic/25/x86_64/docker-host ref within the ostree repo gets
updated.

This fedora-atomic/25/x86_64/docker-host ref is the one that our users
running atomic host are following. It means that when they run
`rpm-ostree upgrade` they are getting the latest commit from the last
bodhi run, not the commit from the last two week release.

We'd like to change this so that user's only get new commits ~every
two weeks (when we do a release). We can achieve this by making a 
few changes:

- change bodhi ostree composes to update a different "ref"
    - we are proposing this ref should be called 
      "fedora-atomic/25/x86_64/updates/docker-host"
      since it tracks the updates yum repo
    - alternatively we already have 
      fedora-atomic/25/x86_64/testing/docker-host
      which tracks the updates-testing yum repo.
      In the future we will change this name to 
      "updates-testing" vs just "testing"

- updating the two week release process to update the 
  fedora-atomic/25/x86_64/docker-host ref
    - This means that ref will only get updated when we do a release.

- building the iso/cloud images from the "updates" ref
  but pointing them to the 2wk release ref
    - This will mean we can still get new images every night to test
      but when we release one of these images it tracks the 2wk ref
      by default.

I've talked with patrick and these changes are pretty simple to make.
We welcome feedback, but hope to implement these changes soon.

I'll be updating ticket 6545 with this information as well. Please
comment with any discussion in the ticket!

Dusty

[1] https://pagure.io/releng/issue/6545
[2] https://fedorahosted.org/rel-eng/ticket/6313