[OpenStack-Infra] Cross-Repo Dependencies in Zuul

Boris Pavlovic boris at pavlovic.me
Tue Feb 10 22:42:50 UTC 2015


Anita,


By "guys" I refer to whole infra team including women...
P.S. I thought that "guys" is gender-neutral....


Best regards,
Boris Pavlovic

On Wed, Feb 11, 2015 at 1:34 AM, Anita Kuno <anteaya at anteaya.info> wrote:

> On 02/10/2015 05:26 PM, Boris Pavlovic wrote:
> > James,
> >
> > Awesome! Amazing! You guys rock!=)
> Hopefully the women do too.
>
> Anita.
> >
> > Best regards,
> > Boris Pavlovic
> >
> >
> >
> > On Wed, Feb 11, 2015 at 1:26 AM, James E. Blair <corvus at inaugust.com>
> wrote:
> >
> >> Hi,
> >>
> >> We have added support for cross-repo dependencies (CRD) in Zuul.  The
> >> important bits:
> >>
> >> * To use them, include "Depends-On: <gerrit-change-id>" in the footer of
> >>   your commit message.  Use the full Change-ID ('I' + 40 characters).
> >>
> >> * These are one-way dependencies only -- do not create a cycle.
> >>
> >> * This is what all the grey dots and lines are in the check pipeline.
> >>
> >> Cross-Repo Dependencies Explained
> >> =================================
> >>
> >> There are two behaviors that might go by the name "cross-repo
> >> dependencies".  We call them one-way and multi-way.
> >>
> >> Multi-way CRD allow for bidirectional links between changes.  For
> >> instance, A depends on B and B depends on A.  The theory there is that
> >> both would be tested together and merged as a unit.  This is _not_ what
> >> we have implemented in Zuul.  Discussions over the past two years have
> >> revealed that this type of behavior could cause problems for continuous
> >> deploments as it means that two components must be upgraded
> >> simultaneously.  Not supporting this behavior is a choice we have made.
> >>
> >> One-way CRD behaves like a directed acyclic graph (DAG), like git
> >> itself, to indicate a one-way dependency relationship between changes in
> >> different git repos.  Change A may depend on B, but B may not depend on
> >> A.  This is what we have implemented in Zuul.
> >>
> >> Gate Pipeline
> >> =============
> >>
> >> When Zuul sees CRD changes, it serializes them in the usual manner when
> >> enqueuing them into a pipeline.  This means that if change A depends on
> >> B, then when they are added to the gate pipeline, B will appear first
> >> and A will follow.  If tests for B fail, both B and A will be removed
> >> from the pipeline, and it will not be possible for A to merge until B
> >> does.
> >>
> >> Note that if changes with CRD do not share a change queue (such as the
> >> "integrated gate" then Zuul is unable to enqueue them together, and the
> >> first will be required to merge before the second is enqueued.
> >>
> >> Check Pipeline
> >> ==============
> >>
> >> When changes are enqueued into the check pipeline, all of the related
> >> dependencies (both normal git-dependencies that come from parent commits
> >> as well as CRD changes) appear in a dependency graph, as in gate.  This
> >> means that even in the check pipeline, your change will be tested with
> >> its dependency.  So changes that were previously unable to be fully
> >> tested until a related change landed in a different repo may now be
> >> tested together from the start.
> >>
> >> All of the changes are still independent (so you will note that the
> >> whole pipeline does not share a graph as in gate), but for each change
> >> tested, all of its dependencies are visually connected to it, and they
> >> are used to construct the git references that Zuul uses when testing.
> >> When looking at this graph on the status page, you will note that the
> >> dependencies show up as grey dots, while the actual change tested shows
> >> up as red or green.  This is to indicate that the grey changes are only
> >> there to establish dependencies.  Even if one of the dependencies is
> >> also being tested, it will show up as a grey dot when used as a
> >> dependency, but separately and additionally will appear as its own red
> >> or green dot for its test.
> >>
> >> (If you don't see grey dots on the status page, reload the page to get
> >> the latest version.)
> >>
> >> Multiple Changes
> >> ================
> >>
> >> A Gerrit change ID may refer to multiple changes (on multiple branches
> >> of the same project, or even multiple projects).  In these cases, Zuul
> >> will treat all of the changes with that change ID as dependencies.  So
> >> if you say that a tempest change Depends-On a change ID that has changes
> >> in nova master and nova stable/juno, then when testing the tempest
> >> change, both nova changes will be applied, and when deciding whether the
> >> tempest change can merge, both changes must merge ahead of it.
> >>
> >> A change may depend on more than one Gerrit change ID as well.  So it is
> >> possible for a change in tempest to depend on a change in devstack and a
> >> change in nova.  Simply add more "Depends-On:" lines to the footer.
> >>
> >> Cycles
> >> ======
> >>
> >> If a cycle is created by use of CRD, Zuul will abort its work very
> >> early.  There will be no message in Gerrit and no changes that are part
> >> of the cycle will be enqueued into any pipeline.  This is to protect
> >> Zuul from infinite loops.  I hope that we can improve this to at least
> >> leave a message in Gerrit in the future.  But in the meantime, please be
> >> cognizant of this and do not create dependency cycles with Depends-On
> >> lines.
> >>
> >> Examples
> >> ========
> >>
> >> The following two infra changes have been tested together because of the
> >> Depends-On: line in the commit message of the first:
> >>
> >>   https://review.openstack.org/#/c/152508/
> >>   https://review.openstack.org/#/c/152504/
> >>
> >> In fact, you can see earlier test results failing until it was rechecked
> >> after CRD went into production (around 2015-02-10 15:20 UTC).
> >>
> >> This devstack change depended on a grenade change:
> >>
> >>   https://review.openstack.org/#/c/154575/
> >>   https://review.openstack.org/#/c/153702/
> >>
> >> And with CRD, was able to be tested in check together as well as being
> >> enqueued into the gate at the same time as its dependency.
> >>
> >> Note that in this example, the Gerrit change ID that 154575 depends on
> >> is actually associated with two changes on two separate branches.  In
> >> cases such as this, Zuul treats all instances as dependencies (so both
> >> changes would be tested together, and both must merge before 154575
> >> may).
> >>
> >> Further Questions
> >> =================
> >>
> >> This is a fairly substantial new feature, and we may still have a bit to
> >> learn about it.
> >>
> >> If you have any further questions, feel free to ask here or in the
> >> #openstack-infra channel on Freenode.
> >>
> >> We will update the infra manual soon to reflect this change.
> >>
> >> -Jim
> >>
> >> _______________________________________________
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> >> OpenStack-Infra at lists.openstack.org
> >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-infra
> >>
> >
> >
> >
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