JenkinsFile.md

JenkinsFile explanation

The plugins installed into Jenkins enhance what is available to the Groovy Pipeline DSL. The values.yaml files we used has several plugins, including the kubernetes plugin.

Based on the Scaling Docker with Kubernetes article, automates the scaling of Jenkins agents running in Kubernetes.

The plugin creates a Kubernetes Pod for each agent started, defined by the Docker image to run, and stops it after each build.

Agents are launched using JNLP, so it is expected that the image connects automatically to the Jenkins master. For that some environment variables are automatically injected:

JENKINS_URL: Jenkins web interface url JENKINS_SECRET: the secret key for authentication JENKINS_NAME: the name of the Jenkins agent

podTemplate

The podTemplate is a template of a pod that will be used to create agents. It can be either configured via the user interface, or via pipeline.

node

node is a special step that schedules the contained steps to run by adding them to Jenkins’ build queue. Even better, requesting a node leverages Jenkins’ distributed build system. Of course, to select the right kind of node for your build, the node element takes a label expression node("test")

The node step also creates a workspace: a directory specific to this job where you can check out sources, run commands, and do other work. Resource-intensive work in your pipeline should occur on a node. You can also use the ws step to explicitly ask for another workspace on the current slave, without grabbing a new executor slot. Inside its body all commands run in the second workspace.

stage

Stages are usually the topmost element of Workflow syntax. Stages allow you to group your build step into its component parts. By default, multiple builds of the same workflow can run concurrently.

Declarative pipelines

pipeline {
  agent {
    kubernetes {
      label 'mypod'
      defaultContainer 'jnlp'
      yaml """
apiVersion: v1
kind: Pod
metadata:
  labels:
    some-label: some-label-value
spec:
  containers:
  - name: maven
    image: maven:alpine
    command:
    - cat
    tty: true
  - name: busybox
    image: busybox
    command:
    - cat
    tty: true
"""
    }
  }
  stages {
    stage('Run maven') {
      steps {
        container('maven') {
          sh 'mvn -version'
        }
        container('busybox') {
          sh '/bin/busybox'
        }
      }
    }
  }
}