Jenkins -> Looping trough Docker-Agents

Question

I want to build some Packages using several Docker-Images in a Jenkins-Pipeline . The Pipeline below works .. but I want to implement the Stage(s) is a more "Loop"-ish way ....

pipeline {
  
  agent { label 'docker' }

  stages {

    stage ('Running on ubuntu:20.04') {
      agent {
        docker {
          reuseNode true
          label 'docker'
          image 'ubuntu:20.04'
        }
      }

      steps {
        sh 'uname -a && bash --version'
      }
    }

    stage ('Running on ubuntu:22.04') {
      agent {
        docker {
          reuseNode true
          label 'docker'
          image 'ubuntu:22.04'
        }
      }
      steps {
        sh 'uname -a && bash --version'
      }
    }
  }
}

An Ideas how to implement that ? ..

Initially I tried using something like this

pipeline {
  agent { label 'docker' }

  stages {
    stage ('Loop-Stage') {
      steps {
        script {
     
          // Loop trough List (*works*)
          for (item in ['ubuntu:20.04', 'ubuntu:22.04']) {
            
            // Create new stage (*works*)
            stage ('Running on ${item}') {
              
              // Set agent (*fails*)
              agent {
                docker {
                  reuseNode true
                  label 'docker'
                  image "${item}"
                }
              }

              steps {
                sh 'uname -a && bash --version'
              }
            }
          }
        }
      }
    }
  }
}

But this does now work. The Error seems to indicate a mixture between scripted&declarative Syntax .. you get the following error:

java.lang.NoSuchMethodError: No such DSL method 'agent' found among steps [ArtifactoryGradleBuild, MavenDescriptorStep, addInteractivePromotion, ansiColor, archive, artifactoryBuildTrigger, artifactoryDistributeBuild, artifactoryDownload, artifactoryEditProps, artifactoryGoPublish, ar

How can I apply a the corresponding "agent" to the dynamically generated Stage ?

Answer 1

When you go into a script block you can no longer use some of the declarative syntaxes like agent. That's why you are getting the error java.lang.NoSuchMethodError: No such DSL method 'agent'. Jenkins is confused about whether you are trying to use Declarative Pipeline syntax or just scripted syntax with groovy.

You can do something like this. This will create a list of stages and then execute them in parallel.

def stageList

def getStages(image) {
    return {
        stage("Running on Ubunt:${image}") {
          docker.image("ubuntu:${image}").inside {
                sh 'uname -a'
            }
        }
    }
}

pipeline {
agent any
  stages {
      
    stage ("Generate Stages") {
        steps {
            script {
                def imageList = ["20.04", "22.04"]
                stageList = imageList.collectEntries {
                        ["${it}" : getStages(it)]}
                    }
                
            }
        }

        stage("Run Stages") {
            steps {
                    script {
                        parallel stageList
                    }
                }
        }
        
    }
}

If you want sequential execution, you can modify your pipeline as shown below.

pipeline {
  agent { label 'docker' }

  stages {
    stage ('Loop-Stage') {
      steps {
        script {
     
          // Loop trough List (*works*)
          for (item in ['ubuntu:20.04', 'ubuntu:22.04']) {
            
            // Create new stage (*works*)
            stage ('Running on ${item}') {
              
            docker.image("${item}").inside {
                sh 'uname -a'
                sh 'uname -a && bash --version'
            }
            }
          }
        }
      }
    }
  }
}