Jenkins – How to wait for user input in a Declarative Pipeline without blocking a heavyweight executor

Jenkinsjenkins-pipeline

I'm rebuilding an existing build pipeline as a jenkins declarative pipeline (multi-branch-pipeline) and have a problem handling build propagation.

After packaging and stashing all relevant files the pipeline is supposed to wait for user input to trigger deployment.

If i just add an input step the current build-node is blocked. As this executor is pretty heavy i would like to move this step to a more lightweight machine.

Initially i did the job as a scripted pipeline and just created two different node('label') blocks. is there a way for me to do something similar with the declarative syntax?

node('spine') { 
    stage('builder') {
        sh 'mvn clean compile'
        stash name: 'artifact', includes: 'target/*.war'
    }
}
node('lightweight') {
    stage('wait') {
        timeout(time:5, unit:'DAYS') {
            input message:'Approve deployment?'
        }
    }
    // add deployment stages
}

I tried a couple of things already:

configuring the agent on the top-level and adding an additional agent config to the propagation step, but then i have two executors blocking as the top-level defined build-node is not stopped.

Setting agent none on top-level and configuring the agents per step. then the git checkout is not present on the first node.

EDIT 1

i reconfigured my pipeline following you advice, it currently looks like this:

pipeline {
agent none
tools {
    maven 'M3'
}
stages {
    stage('Build') {
        agent { label 'spine' }
        steps {
            checkout scm // needed, otherwise the workspace on the first step is empty
            sh "mvn clean compile"
        }
    }
    stage('Test') {
        agent { label 'spine' }
        steps {
            sh "mvn verify" // fails because the workspace is empty aggain
            junit '**/target/surefire-reports/TEST-*.xml'
        }
    }
}
}

this build will fail because the workspace does not carry over between steps as they dont run on the same executor.

EDIT 2

apparently sometimes the steps run on the same executor and sometimes don't. (we spawn build slaves on our mesos/dcos cluster on demand, so changing the executor mid build would be a problem)

I expected jenkins to just run with the current executor as long as the label in the agent definition does not change.

Best Answer

See best practice 7: Don’t: Use input within a node block. In a declarative pipeline, the node selection is done through the agent directive.

The documentation here describes how you can define none for the pipline and then use a stage-level agent directive to run the stages on the required nodes. I tried the opposite too (define a global agent on some node and then define none on stage-level for the input), but that doesn't work. If the pipeline allocated a slave, you can't release the slave for one or more specific stages.

This is the structure of our pipeline:

pipeline {
  agent none
  stages {
    stage('Build') {
      agent { label 'yona' }
      steps {
        ...
      }
    }
    stage('Decide tag on Docker Hub') {
      agent none
      steps {
        script {
          env.TAG_ON_DOCKER_HUB = input message: 'User input required',
              parameters: [choice(name: 'Tag on Docker Hub', choices: 'no\nyes', description: 'Choose "yes" if you want to deploy this build')]
        }
      }
    }
    stage('Tag on Docker Hub') {
      agent { label 'yona' }
      when {
        environment name: 'TAG_ON_DOCKER_HUB', value: 'yes'
      }
      steps {
        ...
      }
    }
  }
}

Generally, the build stages execute on a build slave labeled "yona", but the input stage runs on the master.

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