Triggering Branch Indexing on Multibranch Pipeline

Question

I'm trying to automatically trigger 'Branch Indexing' on a Multibranch Pipelines job in Jenkins.

At the moment, only one method seems to actually work, which is polling, but I am unable to do that and polling is a bad solution anyway.

The plug-in doesn't support 'Trigger builds remotely (e.g., from scripts)' (options are not saved), so I cannot trigger it via a web hook on push etc.

I tried creating a 'trigger' freestyle build on the repo but the 'Post-build Actions - Build other projects' claims the Multibranch Pipeline project is not a buildable project.

If polling is the only way I can do this, then I need to disable automatic SCM triggering (otherwise we get duplicate builds when we re-index) because I'll need to enable web hook triggering on the branch projects.

But that doesn't work, because I'm setting up the web hook via a pipeline script in the branch project, and you need to have built it at least once to have that property registered.

I've been going around in circles for a while, so hopefully I've just missed something obvious, but any help would be appreciated.

I imagined being able to do one of the following

• Somehow trigger the multi-branch project as a downstream project

• Poll the multibranch project, and only build branch projects which have not been built before

Cheers

Answer 1

Based on @jjc's answer, I've created a version using the build step also for triggering the scan:

String downStreamProject = 'my-folder/my-multibranch-project'
String downStreamJob = "${downStreamProject}/${env.BRANCH_NAME}"
if (Jenkins.instance.getItemByFullName(downStreamJob) == null) {
    // we would need "wait: true", which is not possible as of now
    // https://github.com/jenkinsci/pipeline-build-step-plugin/blob/3ff14391fe27c8ee9ccea9ba1977131fe3b26dbe/src/main/java/org/jenkinsci/plugins/workflow/support/steps/build/BuildTriggerStepExecution.java#L66
    build job: downStreamProject, wait: false
    // continue only once the expected job appears
    while (Jenkins.instance.getItemByFullName(downStreamJob) == null) {
        sleep(1)
    }
}
build downStreamJob

This requires the following signatures to be approved:

• method jenkins.model.Jenkins getItemByFullName java.lang.String
• staticMethod jenkins.model.Jenkins getInstance

Answer 2

The method ComputedFolder.scheduleBuild() can be invoked from a groovy script.

I have just triggered branch indexing in one multibranch pipeline project from the groovy code in a different multibranch pipeline project, which is then triggering a downstream build in that project.

The code is something like:

@NonCPS
void scanRepo(String downStreamProjectName) {
    Jenkins.instance.getItemByFullName(downStreamProjectName).scheduleBuild()
}
...
String downStreamProject = 'my-folder/my-multibranch-project'
String downStreamJob = "${downStreamProject}/${env.BRANCH_NAME}"
if (Jenkins.instance.getItemByFullName(downStreamJob) == null) {
    scanRepo(downStreamProject)
    while (Jenkins.instance.getItemByFullName(downStreamJob) == null) {
        sleep(1)
    }
}
build([job: downStreamJob, wait: false, quietPeriod: 0])

Notice that Jenkins.instance.getItemByFullName(downStreamProjectName) is the WorkflowMultiBranchProject which is not Serializable, so some care needs to be taken.

Answer 3

The easiest option by far (that I'm aware of) is to remotely tell the Jenkins Git plugin that there's a new commit for a defined repository. However, this will not trigger Jenkins to start a job immediately. What happens is that the Git plugin starts (re-)indexing the specific repository. The Jenkins job is then started if changes are detected.

From your repository (GitHub, GitLab, etc.) you should trigger the following URL:

http://my-jenkins-host/git/notifyCommit?url=[e-mail]:group/repository.git&delay=0sec

The value for url must match the SCM URL you configured in the Jenkins job (Git plugin)!

Gotcha: it may be that your Jenkins is not deployed under the root context (/) in which case the URL would be http://my-jenkins-host/context-path/git/...