Triggers

The process of merging a change starts with proposing a change to be merged. Currently Zuul only supports Gerrit as a triggering system. Zuul's design is modular, so alternate triggering and reporting systems can be supported. However, Gerrit has a particularly robust data model, and Zuul does make some assumptions that include that data model. Nonetheless, patches to support alternate systems are welcome.

Gerrit

Zuul works with standard versions of Gerrit by invoking the gerrit stream-events command over an SSH connection. It also reports back to Gerrit using SSH.

Gerrit Configuration

Zuul will need access to a Gerrit user. Consider naming the user Jenkins so that developers see that feedback from changes is from Jenkins (Zuul attempts to stay out of the way of developers, most shouldn't even need to know it's there).

Create an SSH keypair for Zuul to use if there isn't one already, and create a Gerrit user with that key:

cat ~/id_rsa.pub | ssh -p29418 gerrit.example.com gerrit create-account --ssh-key - --full-name Jenkins jenkins

Give that user whatever permissions will be needed on the projects you want Zuul to gate. For instance, you may want to grant Verified +/-1 and Submit to the user. Additional categories or values may be added to Gerrit. Zuul is very flexible and can take advantage of those.

Zuul References

As the DependentPipelineManager may combine several changes together for testing when performing speculative execution, determining exactly how the workspace should be set up when running a Job can be complex. To alleviate this problem, Zuul performs merges itself, merging or cherry-picking changes as required and identifies the result with a Git reference of the form refs/zuul/<branch>/Z<random sha1>. Preparing the workspace is then a simple matter of fetching that ref and checking it out. The parameters that provide this information are described in launchers.

These references need to be made available via a Git repository that is available to Jenkins. You may accomplish this by either allowing Zuul to push the references back to Gerrit, in which case you may simply use the Gerrit Git repository. If you do not have access to the Gerrit repository, or would prefer Zuul not push its refs there, you may directly serve the Git repositories that Zuul uses, and configure Jenkins to use those. Instructions for each of these alternatives are in the following sections.

Pushing to Gerrit

If you want to push Zuul refs back to Gerrit, set the following permissions for your project (or All-Projects) in Gerrit (where CI Tools is a group of which the user you created above is a member):

[access "refs/zuul/*"]
        create = group CI Tools
        push = +force CI Tools
        pushMerge = group CI Tools
[access "refs/for/refs/zuul/*"]
        pushMerge = group CI Tools

And set push_change_refs to true in the zuul section of zuul.conf.

Serving Zuul Git Repos

Zuul maintains its own copies of any needed Git repositories in the directory specified by git_dir in the zuul section of zuul.conf (by default, /var/lib/zuul/git). If you want to serve Zuul's Git repositories in order to provide Zuul refs for Jenkins, you can configure Apache to do so using the following directives:

SetEnv GIT_PROJECT_ROOT /var/lib/zuul/git
SetEnv GIT_HTTP_EXPORT_ALL

AliasMatch ^/p/(.*/objects/[0-9a-f]{2}/[0-9a-f]{38})$ /var/lib/zuul/git/$1
AliasMatch ^/p/(.*/objects/pack/pack-[0-9a-f]{40}.(pack|idx))$ /var/lib/zuul/git/$1
ScriptAlias /p/ /usr/lib/git-core/git-http-backend/

And set push_change_refs to false (the default) in the zuul section of zuul.conf.

Note that Zuul's Git repositories are not bare, which means they have a working tree, and are not suitable for public consumption (for instance, a clone will produce a repository in an unpredictable state depending on what the state of Zuul's repository is when the clone happens). They are, however, suitable for automated systems that respond to Zuul triggers.

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