Jenkins – Docker as a pipeline agent.

In another step in configuring Jenkins for pipelines, in this post I will show how to use Docker Container as an Agent, K8s Pods can also be used, but I will show this in another post later on.

The use of containers as an agent opens up a huge variety and possibility of processes, in any language, in any way you want, whatever you can do in a conventional container. I use a lot of scripts in Python, and this way I can create many processes, including with Ansibles, accessing other services, taking advantage of many code modules that exist.

For this example, I created an image in Ubuntu, very simple, just with Python, which will serve as the base image for the pipelines. https://devops-db.com/base-image-for-docker-python/

Let’s start configuring Jenkins, the first step is to install the Docker Plugin.
With an administrative account in Jenkins, open Manage Jenkins / Cloud. Click Install Plugin: Docker

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Then, in the same Manage Jenkins / Cloud, there will be one more option: New Cloud, click on the option.

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Choose a name for the Cloud and choose the Docker type.

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This option should open a series of configuration options. Enter the Docker Host URI, in my case the IP is 172.21.5.70 and as it is on the same host as Jenkins, I do not need to create credentials. Check the Enable option and do a Test Connection. Save, the configuration is that simple.

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On your Docker host, you may need to change permissions due to unix:///var/run/docker.sock.
Adding the user jenkins to the docker group already solves the problem, in the worst case, for testing, apply chmod 777 to the /var/run/docker.sock file (This option should not be applied in a production environment)

Now you need to install a second plugin, again in Manage Jenkins / Plugins / Available Plugins: Install the Docker Pipeline plugin

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Restart Jenkins to take effect the changes.

Now, let’s change the groovy pipeline script we made in the previous post. Change the script and merge it into Master from the repository http://gitlab.devops-db.internal/infrastructure/pipelines/dns

pipeline {
    agent any
    options { timestamps () }
    stages {
        stage('Build') {
            when { not { changeRequest() } }
            agent {
                docker {
                    image 'ubuntu_python:3.10.6'
                }
            }            
            steps {
                updateGitlabCommitStatus name: 'Finish', state: 'pending'
                sh 'printenv'
                sh 'ls -lah ${WORKSPACE}'
                updateGitlabCommitStatus name: 'Finish', state: 'success'
            }
        }
        stage('Finish') {
            when { branch 'master' }
            agent {
                docker {
                    image 'ubuntu_python:3.10.6'
                }
            }            
            steps {
                updateGitlabCommitStatus name: 'Finish', state: 'pending'
                sh 'printenv'
                updateGitlabCommitStatus name: 'Finish', state: 'success'
            }
        }
    }
}

Make any commit / push to the GitLab project we use for testing this pipeline and see the result:

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