Friday, September 18, 2015

Mozharness' support for Buildbot Bridge triggered test jobs

I have landed today [1] some code which allows Buildbot *test* jobs triggered through the Buildbot Bridge (BBB) to work properly.

In my previous post I explain a bit on how Mozci works with the Buildbot Bridge.
In this post I will only explain what we fixed on the Mozharness side.

Buildbot Changes

If a Buildbot test job is scheduled through TaskCluster (The Buildbot Bridge supports this), then the generated Buildbot Change associated to a test job does not have the installer and
test urls necessary for Mozharness to download for a test job.

What is a Buildbot Change? It is an object which represents the files touched associated to a code push. For the build jobs, this value gets set as part of the process of polling the Mercurial repositories, however, the test jobs are triggered via  a "buildbot sendchange" step part of the build job.
This sendchange creates the Buildbot Change for the test job which Mozharness can then use.
The BBB does not listen to sendchanges, hence, jobs triggered via the BBB have an empty changes object. Therefore, we can't download the files needed to run a test job and fail to execute.

In order to overcome this limtation, we have to detect when a Buildbot job is triggered normally or through the Buildbot Bridge.
Buildbot Bridge triggered jobs have a 'taskId' property defined (this represents the task associated to this Buildbot job). Through this 'taskId' we can determine the parent task and find a file called properties.json [2], which, it is uploaded by every BBB triggered job.
In such file, we can find both the installer and test urls.