CI/CD as Code Part IV - Stateless Jenkins : Jobs as Code - Advanced

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In the previous article of these examples , we created a stateless jenkins container which can be initialised solely by using scripts. In that example, a seed job for jobdsl plugin was also implemented. This job was later on used to create an automated simple jenkins job inline. In order to create more complex jobs in an automated fashion, we will extend previous seed job implementation further in this example. Our extended seedJob will poll a job definition repository to gather the information on how to create new complex jobs for some other remote repositories.
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CI/CD as Code Part II - Installing and Setting up Jenkins by Code

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The purpose of these sample series is to create a simple set of examples, which showcasesCI/CD as Code, using Jenkins. Primary 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.
We created a containerised Jenkins instance in the previous part of these example series. Most of the installation and setup work in that example was done manually via user interface. Our target in this step is to automate most of the manual work in our way towards a stateless Jenkins instance. 
Checkout this example from here

In summary, this basic setup will handle the following on behalf of an actual human being:

  1. Creation of the user(s) on jenkins programmatically.
  2. Installation of basic plugins to get up-and-running with Jenkins.

Creating the initial admin user for Jenkins programmatically

Jenkins provides a set of scripted execution mechanisms to allow automation in delivery processes using certain key Jenkins events. This mechanism is called "hook scripts". In this step, we are going to introduce "Post-initialization scripts" from this set to our container.
In a standard Jenkins setup, "post-initialization" scripts are located at /usr/share/jenkins/ref/init.groovy.d/. In order to use this feature in our container, let's add a folder named init.groovy to our code base and map the contents of this folder to our container's post-initialization scripts directory:
Add the following command to your Dockerfile
ADD init.groovy/ /usr/share/jenkins/ref/init.groovy.d/
Next step is to implement the script, which will create the initial admin user for us. Create a groovy script file under init.groovy named "0-disable-login.groovy" directory and paste the following code:
Note that, post-initialization scripts are executed in alphabetical order by Jenkins. This is why the prefix "0" is used for user creation script.

Adding initial set of necessary jenkins plugins programmatically

In this step, we need to collect a list of necessary jenkins plugins for our setup. For the purpose of keeping the example simple, you can use recommended plugins in a standard jenkins installation. In order to get this list, run your container created in the previous step and complete the setup via user interface. When the setup is finished, you can either use jenkins scripting interface located at " http://yourhost:port/script" or use the api provided by Jenkins.
Getting the lis using a script:
Getting the list using the api:
curl --user admin_groovy:123456  "http://localhost:7080/pluginManager/api/json?depth=1"
After getting the list of plugins, create a file named plugins under configs directory and paste the shortnames of the plugins to this file.
Excerpt of the plugins file:
ace-editor
ant
antisamy-markup-formatter
apache-httpcomponents-client-4-api
authentication-tokens
bouncycastle-api
branch-api
build-timeout
cloudbees-folder
...
Now that we have our list of necessary plugins, it's time to install them within our container. Add the following lines to your Dockerfile. 
COPY configs/plugins /var/jenkins_init_config/plugins
RUN /usr/local/bin/install-plugins.sh < /var/jenkins_init_config/plugins
The container can be tested after completing this step. Build your container, run it and check if everything works as expected from the user interface.

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