PullRequest Build Validation with Jenkins and OnPrem Az-Devops - jenkins

Question

First off the setup in question:
A Jenkins Instance with several build nodes and on prem Azure-Devops server containing the Git Repositories.
The Repo in question is too large to always build on push for all branches and all devs, so a small workaround was done:
The production branches have a polling enabled twice a day (because of testing duration which is handled downstream more builds would not help with quality)
All other branches have their automated building suppressed. They still can start it manually for Builds/Deployments/Unittests if they so choose.
The jenkinsfile has parameterization for which platforms to build, on prod* all the platforms are true, on all other branches false.
This helps because else the initial build of a feature branch would always build/deploy locally all platforms which would take too much of a load on the server infrastructure.
I added a service endpoint for Jenkins in the Azure Devops, added a Buildvalidation .yml - this basically works because when I call the sourcebranch of the pull request with the merge commitID i added a parameter
isPullRequestBuild which contains the ID of the PR.
snippet of the yml:
- task: JenkinsQueueJob#2
inputs:
serverEndpoint: 'MyServerEndpoint'
jobName: 'MyJob'
isMultibranchJob: true
captureConsole: true
capturePipeline: true
isParameterizedJob: true
multibranchPipelineBranch: $(System.PullRequest.SourceBranch)
jobParameters: |
stepsToPerform=Build
runUnittest=true
pullRequestID=$(System.PullRequest.PullRequestId)
Snippet of the Jenkinsfile:
def isPullRequest = false
if ( params.pullRequestID?.trim() )
{
isPullRequest = true
//do stuff to change how the pipeline should react.
}
In the jenkinsfile I look whether the parameter is not empty and reset the platforms to build to basically all and to run the unittests.
The problem is: if the branch has never run, Jenkins does not already know the parameter in the first run, so it is ignored, building nothing, and returning with 0 because "nothing had to be done".
Is there any way to only run the jenkins build if it hasnt run already?
Or is it possible to get information from the remote call if this was the build with ID 1?
The only other thing would be to Call the Jenkins via web api and check for the last successful build, but in that case I would have have the token somewhere stored in source control.
Am I missing something obvious here? I dont want to trigger the feature branch builds to do nothing more than once, because Devs could lose useful information about their started builds/deployments.
Any ideas appreciated

Answer 1

To whom it may concern with similar problems:
In the end I used the following workaround:
The Jenkins Endpoint is called via a user that only is used for automated builds. So, in case that this user triggered the build, I set everything to run a Pull Request Validation, even if it is the first build. Along the lines of
def causes = currentBuild.getBuildCauses('hudson.model.Cause$UserIdCause')
if (causes != null)
{
def buildCauses= readJSON text: currentBuild.getBuildCauses('hudson.model.Cause$UserIdCause').toString()
buildCauses.each
{
buildCause ->
if (buildCause['userId'] == "theNameOfMyBuildUser")
{
triggeredByAzureDevops = true
}
}
}
getBuildcauses must be allowed to run by a Jenkins Admin for that to work.