Stage Specific Agents

In this lab we will get an introduction to the Jenkins Kubernetes plugin that enables the use of dynamic and ephemeral agents with CloudBees CI on a Kubernetes cluster - allowing you to leverage the scaling capabilities of Kubernetes to schedule build agents.

CloudBees CI has out-of-the-box support for Kubernetes build agents, with the capability to create and manage Kubernetes agent templates - called Pod Templates - at both the the Cloud Operations Center level to be shared by multiple controllers and at the the Managed Controller level for more granular agent configuration. The Kubernetes based agent is contained in a Kubernetes pod, where a pod is a group of one or more containers (e.g. Docker container) sharing a common storage system and network. A pod is the smallest deployable unit of computing that Kubernetes can create and manage (you can read more about pods in the Kubernetes documentation).

We will use the Kubernetes plugin Pipeline container block to run Pipeline steps inside a specific container configured as part of a Jenkins Kubernetes Agent Pod template. In our initial Pipeline, we used agent any which required at least one Jenkins agent configured to Use this node as much as possible - resulting in the use of a Pod Template that only had a jnlp container. But now we want to use Node.js in our Pipeline. Jenkins CasC was used to pre-configure the CloudBees Kube Agent Management plugin to include a Kubernetes Pod Template at the managed controller level to provide a Node.js container.

1. In the pipelines folder on your controller, click on the simple-pipeline-job link and then click on the Pod Templates link.
2. The Available pod templates screen will show you what pod templates are available to use on your controller and includes the Label to use for the agent and lists the Containers configured for the template. Note the label, container name and image for the nodejs-app template.
3. Navigate to and click on the Jenkinsfile file in the add-jenkinsfile branch of your insurance-frontend repository and click on the Edit this file button (pencil) and replace the global agent section with the following:

  agent none

4. Next, in the Say Hello stage add the following agent section right above the steps section so that we will get the Kubernetes Pod Template configured for your Managed Controller with the Container Template that includes the us-east1-docker.pkg.dev/core-workshop/workshop-registry/node:14-alpine Docker(container) image above:

    agent { label 'nodejs-app' }

pipeline {
  agent none
  stages {
    stage('Say Hello') {
      agent { label 'nodejs-app' }
      steps {
        echo 'Hello World!'   
        sh 'java -version'
      }
    }
  }
}

5. Commit that change to the add-jenkinsfile branch and navigate to your insurance-frontend job on your Managed Controller. The build logs should be almost the same as before because we are still using the default jnlp container.
6. Let’s change that by replacing the Say Hello stage with the following Test stage so the steps run in the nodejs container. Edit the Jenkinsfile file in the add-jenkinsfile branch of your forked insurance-frontend repository so the entire pipeline looks like the following:

pipeline {
  agent none
  stages {
    stage('Test') {
      agent { label 'nodejs-app' }
      steps {
        container('nodejs') {
          echo 'Hello World!'   
          sh 'java -version'
        }
      }
    }
  }
}

All of the Pipeline steps within the container block will run in the container specified by the Name of the Container Template - and in this case that Container Template is using the us-east1-docker.pkg.dev/core-workshop/workshop-registry/node:14-alpine container image as we saw above. Commit the changes and the insurance-frontend job will run - it will result in an error because the nodejs container does not have Java installed (and why should it). Hover over the failed stage in the Stage View of your add-jenkinsfile branch job and click on the Logs button. Next, expand the last step - sh 'java -version' - to see the error. 7. We will fix the error in the Test stage we added above by replacing the sh 'java -version' step with the sh 'node --version' step and moving the sh 'java -version step above the container block in the Jenkinsfile file in the add-jenkinsfile branch of your forked insurance-frontend repository so the entire pipeline looks like the following:

pipeline {
  agent none
  stages {
    stage('Test') {
      agent { label 'nodejs-app' }
      steps {
        sh 'java -version'
        container('nodejs') {
          echo 'Hello World!'   
          sh 'node --version'
        }
      }
    }
  }
}

8. Commit the changes and the insurance-frontend add-jenkinsfile branch job will run and it will complete successfully with the following output:

Finished Jenkinsfile for Stage Specific Agents Lab

Important: For the finished Jenkinsfile for this stage, remove the sh 'java -version' step and make sure you copy the Pipeline as below and replace yours.

pipeline {
  agent none
  stages {
    stage('Test') {
      agent { label 'nodejs-app' }
      steps {
        container('nodejs') {
          echo 'Hello World!'   
          sh 'node --version'
        }
      }
    }
  }
}