CI/CD as Code Part III - Stateless Jenkins - Jobs as Code

The purpose of these sample series is to create a simple set of examples, which showcasesCI/CD as Code, using Jenkins. Main goal is to create a stateless CI/CD setup, which can be bootstrapped from a set of configuration files and scripts so that many problems related to maintenance of the infrastructure and other operational issues are reduced.

First Steps to "job as code"

Checkout this example from here
We are going to introduce necessary plugins to achieve the goal of programmatic job descriptions in this step and configure them accordingly via programmatic means.
The first plugin that we are going to introcude is jobDsl plugin. The most common job creation mechanism in Jenkins is that users usually create jobs by cloning/copying an existing project. As experienced by most of us, when the number of jobs grows in Jenkins or the job description gets complicated, use of user interface oriented method becomes more tedious. This is where jobDsl plugin comes in handy. It provides the programmatic bridge to create jobs using scripts or configuration files.
In order to serve it's purpose, jobDsl plugin uses a free style jenkins job, is called "Seed Job". This job is a standard free style job to which you add a "Process Job DSLs" step. This step uses the configured DSL and generates jobs configured in it. (For further information please visit the official tutorial)
That's enough talking. Let's move to the practical part.

Adding jobDsl support and creating a job using dslScript

We introduced automatic plugin installation support to our stateless jenkins instance in the previous step(s). Now we can use our plugin installation file to add our new plugin.
Open configs/plugins file and add job-dsl as a new line to this file
The next step is to configure the seed job by programmatic means. Since we already have the support for "Post-initialization scripts" in our container, we can add a groovy script to create our "Seed Job". Let's add a new groovy script file named 1-init-dsl-seed-job.groovy to our init scripts (init.groovy/1-dsl-seed-job.groovy). Please remember that the reason a numbered prefix is used in the script file names is that these scripts are executed by Jenkins in alphabetical order.
As mentioned earlier, the primary goal of this script is to create the seed job for the plugin. Additionally, we will also add a simple job dsl to the seed job using the "Use the provided DSL script (useScriptText=true)" option. This job, which is going to be created by our seed job, will only print "Hello World!" to the stdout.

Note that, there are more advanced ways to create jobs using the seed job, but simple job definition serves the purpose of this step.

The example job dsl is as follows:

job('example') {
  steps {
    shell('echo Hello World!')
  }
}

The content of the init.groovy/1-dsl-seed-job.groovy script will be as follows:

Test what has been done so far

1. run the docker-compose up --build command against your docker-compose file.
2. Browse to the Jenkins instance http://localhost:7080 and login.
3. Run the SeedJob job.

   The job will fail first time you run it. It's because the jobDsl plugin limits execution of the scripts without admin approval. In order to approve the execution, go to configuration page of the job and click save.

4. Check if a job named example is created.
5. Run the example job and check the output of the job using the console output link on the interface.

Disable Script Security Checks for jobDsl Plugin

If you followed the execution steps in the previous section, you must have noticed the failure of SeedJob and had resolved it manually. Since our goal is to minimize the manual work as much as possible and to get a stateless jenkins instance, we are going to introduce one additional jenkins init script to disable script execution limitation for jobDSL plugin.  The script below does the job for us:

After adding this script to our init.groovy folder, we can repeat the steps mentioned in "Test what has been done" section, but this time without facing the problem mentioned in item 3 of the list there.