Setting up seed job with the Job DSL

Prerequisites

1. Download and run Jenkins
   1. Download Jenkins.
   2. Open up a terminal in the download directory.
   3. Run java -jar jenkins.war --httpPort=8080.
   4. Browse to http://localhost:8080.
   5. Follow the instructions to complete the installation.
2. Familiarity with Jenkins Pipeline.

Part 1. Proof of concept

Now that the prerequisites are out of the way, the first thing we are going to do is set up a simple proof of concept Freestyle project (seedJob) in Jenkins. This job will be used to generate other jobs you want to on-board into Jenkins.

graph LR
A[seedJob] -- generates --> B{simple}

Loading

1. Install the Job DSL plugin

Navigate to http://localhost:8080/ in your browser and login to Jenkins with the credentials you set up. We need to configure Jenkins to use the Jenkins Job DSL API.

• Navigate to Dashboard > Manage Jenkins > Manage Plugins > select Available tab > search for Job DSL and install.

2. Creating the Freestyle Project seedJob

We will set up our seedJob the same way any other job is created.

1. On the left hand side of the page, select New Item
2. In the text box for Enter an item name, enter seedJob > select the Freestyle project > select OK.

3. Configure seedJob to use hola-jenkinsgithub repository

Now we are going to store the code for our seedJob in a github repository called hola-jenkins. Since we are using the hola-jenkins repository to load seed.groovy, we need to configure seedJob to use this repository.

1. Navigate to Dashboard > select seedJob > select Configure.
2. Scroll to the Source Code Management section > select Git.
3. In the Repository URL field, enter https://github.com/hereischen/hola-jenkins.
   • Leave everything else as the default configuration.

4. Configure seedJob to use the seed.groovy file we will store in github

Now that we have configured Jenkins to use our hola-jenkins repository, we need to set up seedJob to load seed.groovy from our hola-jenkins repository. This is necessary for us to start using the Jenkins Job DSL API functionality.

Since we will be using our hola-jenkins repository, we will need to add some additional configuration to the seedJob to get this working.

1. Navigate to Dashboard > select seedJob > select Configure.
2. Scroll to the Build section > select Add Build step > Select Process Job DSLs.
3. Select Look on Filesystem.
4. In the DSL Scripts input field, enter dsl/seed.groovy (this is the path to the seed.groovyfile we will be setting up later).
   • Leave everything else as the default configuration

5. Configure seedJob to take a parameter as the job name

We will give our job the name when we plan to build (simpleJob). In order to do this we will need to add a String parameter to the seedJob that will be used inside of seed.groovy.

1. Navigate to Dashboard > select seedJob > select Configure .
2. Select This project is parameterized > select Add Parameter > select String Parameter.
3. Enter jobName in Name field.
4. In the Description field, enter The name of your job(typo in the image).

6. Creating a simple demo Freestyle job

We are using the hola-jenkins github repository. This repository will be used to store our seed code. Later, we will include our Shared Library code in this repository.

1. Inside of the hola-jenkins repository, we have created a directory dsl with seed.groovy inside.
   • hola-jenkins/dsl/seed.groovy.
2. Below are the contents of seed.groovy.
   • We create a simple Freestyle Job and use the String Param named jobName from seedJob to name our Freestyle job.

job(jobName) {
    description("A simple Freestyle Job generated from seed.groovy")
}

7. Running the seedJob

Now that we have our seedJob setup to read in seed.groovy from our github hola-jenkins repository, we are ready to trigger our seedJob to create a Freestyle job with jobName

1. Navigate to Dashboard > select seedJob > select Build Now.
2. Under Build History, select the top red circle.
3. This will take you to the Console Output.
   • The job failed.
   • Due to Script Security, this will happen every time you change seed.groovy. The Script Security Plugin is integrated with the Job DSL plugin and the Script Security Plugin is set up with a set of scripts that are pre approved for use. Since this is a new script, it will require an admin approval to use.

8. Approving our seed.groovy script

We need to tell Jenkins it is ok to use this script.

• Navigate to Dashboard > Manage Jenkins > In-process Script Approval.
• Select Approve for the seed.groovy script.

Note: We can apply configuration-as-code-plugin to by pass this behavior by adding a hola-jenkins/jenkins.yaml. in our hola-jenkins repository.

security:
    globalJobDslSecurityConfiguration:
      # Otherwise Job DSL either requires script approval or having all config whitelisted
      # https://github.com/jenkinsci/job-dsl-plugin/wiki/Script-Security
      useScriptSecurity: false

Consult JCasC for more information.

9. Rerunning the seedJob

Now that we have approved seed.groovy, we are ready for our seedJob to run (and succeed).

1. Navigate to Dashboard > select seedJob > select Build Now.
2. Under Build History, select the top blue circle.
3. Inside of Console Output, you will see GeneratedJob{name='freestyle'}.
   • Jenkins has created a new job called simple fromseed.groovy.

Part 2. One implementation

1. Introduction

In this second part, we will be setting up a Jenkins Shared library to execute our Jenkins jobs. As the complexity and number of jobs you maintain grow, the use of Shared Libraries provides the ability to share and reuse code across jobs for CI and CD processes.

In order to set up a practical application with our seed, we will modify seed.groovy to build a Pipeline job (composeTrigger) from a file named composeTrigger in Shared Libraries.

graph LR
A[seed] -- generates --> B{composeTrigger}
A[seed] -- generates --> C{acceptanceTrigger}
A[seed] -- generates --> D{otherJobN}

Loading

2. Configure default Shared Library set up for Jenkins

Since we will be using a Shared library, Jenkins needs to be set up to use our Shared Library.

1. Navigate to Dashboard > select Manage Jenkins > select Configure System > scroll down to Global Pipeline Libraries > select Add
2. Enter hola-jenkins in the Name field.
3. Enter new-imp in Default Version.
   • This tells jenkins which branch of our Shared Library we plan to use by default.
4. Under Source Code Management, select Git.
5. In the Project Repository field, enter https://github.com/hereischen/hola-jenkins > select Save.

3. Create seed to use a new-imp branch we will create in hola-jenkins

Create a new job DSL named seed, just like what we did in session 1.2. Under Source Code Management, change the Branch Specifier to */new-imp

1. Create a new branch new-imp in hola-jenkins.
2. In the new-imp branch, remove the original code in seed.groovy and paste in from seed.groovy. This script loads jobs from /vars/jobs and builds each job using its file name as the job name.
   • For a better understanding of the pipelineJob , make sure to go back and check the Jenkins Job DSL API.

#!/usr/bin/env groovy
import groovy.io.FileType

String jobDir = "${WORKSPACE}/vars/jobs"


def retrieveJobs (String jobDir) {
    def list = []
    def dir = new File(jobDir)
    dir.eachFileRecurse (FileType.FILES) { file ->
        list << file.getName()
    }
    return list
}

def buildPipelineJobs(String jobName){
    String repoUrl = "https://github.com/hereischen/hola-jenkins.git"
    println "Seeding job ${jobName}."
    pipelineJob(jobName) {
        definition {
            cpsScm {
                scm {
                    git {
                        remote {
                            url(repoUrl)
                        }
                        branches('new-imp')
                        extensions {
                            cleanBeforeCheckout()
                        }
                    }
                }
                scriptPath("vars/jobs/${jobName}")
            }
        }
        // build jobs to make their properties effective
        queue(jobName)
    }
}

def jobList = retrieveJobs (jobDir)
jobList.each {
    buildPipelineJobs(it)
}

3. Create a new file named composeTrigger(This will be the job name) under vars/jobs

#!/usr/bin/env groovy

// Configure using hola-jenkins
@Library("hola-jenkins@new-imp") _

properties([
    parameters([
        string(name: 'example_param1', defaultValue: 'hello word')
    ]),
])

node {
    stage('Checkout') {
        checkout scm
    }
    stage("Package artifact") {
        sh "echo this is it"
        println("properties:${params.example_param1}")
    }

}

4. Running the seed

All of our configuration is set up and our repository is ready to use. We will now run our seed to create our composeTrigger based on our seed.groovy set up.

1. Navigate to Dashboard > select seedJob -> select Build now