Jenkins multibranch pipeline with Jenkinsfile from different repository

Question

I have a Git repository with code I'd like to build but I'm not "allowed" to add a Jenkinsfile in its root (it is a Debian package so I can't add files to upstream source). Is there a way to store the Jenkinsfile in one repository and have it build code from another repository? Since my code repository has several branches to build (one for each Debian release) this should be a multibranch pipeline. Commits in either the code or Jenkinsfile repositories should trigger a build.

Bonus complexity: I have several code/packaging repositories like this and I'd like to reuse the same Jenkinsfile for all of them. Thus it should somehow dynamically fetch the right Git URL to use. The branches to build have the same names across all repositories.

Answer 1

Short answer is : you cannot do that with a multibranch pipeline. Multibranch pipelines are only designed (at least for now) to execute a specific pipeline in Pipeline script from SCM style, with a fixed Jenkinsfile at the root of the project.

You can however use the Multi-Branch Project plugin made for multibranch freestyle projects. First, you need to define your multibranch freestyle configuration just like you would with a multibranch pipeline configuration. Select this new item like shown below :

This type of configuration will behave exactly same as the multibranch pipeline type, i.e. it will create you a folder with the name of your configuration and a sub-project for each branch it automatically detected.

The implementation should then be a piece of cake :

1. Specify your SCM repository in the multibranch configuration
2. Call another build as part of your build/post-build as you would do in a standard freestyle project, except that you have to call a parameterized job (let's call it build-job) and give it your repository information, i.e. Git URL and current branch (you can use the pre-defined variables $GIT_URL and $GIT_BRANCH for this purpose)
3. In your build-job, just define either an inline pipeline or a pipeline script checked out from SCM, and inside this script do a SCM checkout and go on with the steps you need to build. Example of build-job pipeline content :

.

node() {   stage 'Checkout'   checkout scm: [$class: 'GitSCM', branches: [[name: '*/${GIT_BRANCH}']], userRemoteConfigs: [[url: '${GIT_URL}']]]    stage 'Build'   // Build steps... } 

Of course if your different multibranches projects need to be treated a bit differently, you could also use intermediate projects (let's say build-project-A, build-project-B, ...) that would in turn call the generic build-job pipeline)

The one, major drawback of this solution is that you will only have one job responsible for all of your builds, making it harder to debug. You would still have your multibranch projects going blue/red in case of success/error but you will have to go back to called build-job to find the real problem of your build.