Getting started with Jenkins and Docker

Thu, 15 Aug 2024 00:00:00 +0000

Introduction

Jenkins is one of the most popular and powerful automation tools, widely used for integrating and deploying software projects continuously. While it’s possible to quickly start Jenkins using a simple Docker command, this setup looks like “Hello World” in any programming language: useful for begginers, but insufficient for production environments.

In this post, we go beyond the basics. The goal here is to guide you with some techniques for a (almost) robust and scalable Jenkins architecture using Docker and Docker Compose. We’ll explore fundamental concepts like machine isolation and set up an environment near real world scenario. By the end, you’ll have a solid structure ready to be adapted and expanded according to your needs.

If you’re ready to move from begginer to professional CI/CD environment, read on!

“Environment near real world scenario” does not mean production environment. Use this post as a reference, not a production ready solution.

Prerequisites

Before diving into the technical details, it’s essential to ensure that some prerequisites are met:

Linux (In my case, I use Windows as main SO, so I need to use some virtualizer like WSL, Virtualbox, VmWare, etc.)
Docker

Key Concepts

With the prerequisites defined, we can now explore some key concepts that will guide the Jenkins setup.

Isolation

The first best practice for using Jenkins is not to run everything on the same machine. Both for security and scalability reasons, it is recommended to use at least two machines.

The first machine is what we usually call the controller. It is the main machine, primarily responsible for the interface, settings, and job execution control.

The other machines are called nodes. These machines are responsible for executing all the jobs.

Machine Configuration

Both the controller and the nodes need to be configured within an operating system.

Installing prerequisites, creating directories, and setting user permissions are some examples. Additionally, we will take this opportunity to perform some Jenkins configurations that will only take effect on startup or restart.

We will use the Jenkins images and Docker Compose for this step.

Jenkins Configuration

With Jenkins running, we need to configure the environment to work properly:

Access credentials
Configuration of communication between the controller and the node

These configurations will not be done manually. We will use the Configuration as Code plugin to automate this process.

Basic Structure

With the concepts understood, it’s time to start defining the basic structure of the project.

This is the basic structure. This model will be used in future posts.

.
└── demo/
    ├── casc/                             # Jenkins configuration as code
    │   └── *.yaml
    ├── plugins/
    │   └── plugins.txt                   # Plugin list
    ├── scripts/
    │   └── *.groovy                      # Jenkins initialization scripts
    ├── ssh                               # Public and private keys
    ├── docker-compose.yaml
    ├── Dockerfile
    ├── start.sh
    └── stop.sh

Dockerfile

Within this structure, the Dockerfile plays a central role. Let’s examine it in detail:

FROM jenkins/jenkins:lts

RUN mkdir -p $JENKINS_HOME/.ssh
RUN chown -R jenkins:jenkins $JENKINS_HOME/.ssh
RUN touch $JENKINS_HOME/.ssh/known_hosts
RUN chmod 600 $JENKINS_HOME/.ssh/known_hosts
COPY --chown=jenkins:jenkins ./ssh/jenkins_key  $JENKINS_HOME/.ssh/jenkins_key
RUN chmod 600 $JENKINS_HOME/.ssh/jenkins_key

COPY --chown=jenkins:jenkins ./scripts/ /usr/share/jenkins/ref/init.groovy.d/

COPY --chown=jenkins:jenkins ./plugins/plugins.txt /usr/share/jenkins/ref/plugins.txt
RUN jenkins-plugin-cli -f /usr/share/jenkins/ref/plugins.txt

RUN mkdir -p $JENKINS_HOME/casc_configs
RUN chown -R jenkins:jenkins $JENKINS_HOME/casc_configs
COPY --chown=jenkins:jenkins ./casc/* $JENKINS_HOME/casc_configs/

ENV CASC_JENKINS_CONFIG="$JENKINS_HOME/casc_configs/"
ENV JAVA_OPTS="-Djenkins.install.runSetupWizard=false"

A summary of the Dockerfile content:

lines 3 to 8: Creation of the .ssh directory and copying of the private key stored in the project’s ssh folder.
line 10: Copying of Groovy scripts stored in the project’s scripts folder.
lines 12 and 13: Copying the plugin list and installing the plugins in the image.
lines 15 to 17: Creation of the JCasC plugin folder and copying the configuration files from the project’s casc folder (Configuration as Code).
line 20: Sets the environment variable CASC_JENKINS_CONFIG to configure the default folder where Jenkins will retrieve these files.
line 21: Configures the environment variable JAVA_OPTS to skip the installation Wizard.

docker-compose.yaml

After configuring the Dockerfile, we need to orchestrate the services with docker-compose.yaml:

version: '3.7'
volumes:
  jenkins_data:
    name: jenkins_data
services:
  jenkins:
    container_name: jenkins_master
    build: .
    ports:
      - 8080:8080
      - 50000:50000
    volumes:
      - jenkins_data:/var/jenkins_home/
      - /var/run/docker.sock:/var/run/docker.sock
  ssh-agent:
    container_name: jenkins_agent
    image: jenkins/ssh-agent
    environment:
      - JENKINS_AGENT_SSH_PUBKEY=${JENKINS_AGENT_SSH_PUB}
    depends_on:
      - jenkins

There is no secret to docker-compose. The jenkins service runs the official Jenkins image, with the main ports mapped, and the ssh-agent service will be the execution node for the pipelines.

In line 19, we configure the environment variable JENKINS_AGENT_SSH_PUBKEY to inform the generated public key.

plugins.txt

Now that the services are configured, let’s define the essential plugins in the plugins.txt file:

cloudbees-folder
build-timeout
credentials
timestamper
ws-cleanup
pipeline-milestone-step
pipeline-input-step
pipeline-stage-step
pipeline-graph-analysis
pipeline-rest-api
pipeline-stage-view
pipeline-build-step
pipeline-model-api
pipeline-model-extensions
pipeline-stage-tags-metadata
pipeline-model-definition
ssh-credentials
ssh-slaves
config-file-provider
workflow-aggregator
configuration-as-code

executors.groovy

Following the recommendations at the beginning of the article, it is necessary to adjust the Jenkins executors, which we will do in the executors.groovy script:

1
2

import jenkins.model.*
Jenkins.instance.setNumExecutors(0) // Recommended to not run builds on the built-in node

ssh-agent.yaml

Finally, we need to configure secure communication between the controller and the nodes, using ssh-agent.yaml:

credentials:
  system:
    domainCredentials:
      - credentials:
          - basicSSHUserPrivateKey:
              scope: SYSTEM
              id: ssh_agent_key
              username:
              description: "SSH passphrase with private key file. Private key provided"
              privateKeySource:
                directEntry:
                  privateKey: "${readFile:${JENKINS_HOME}/.ssh/jenkins_key}"
jenkins:
  nodes:
  - permanent:
      launcher:
        ssh:
          credentialsId: "ssh_agent_key"
          host: "jenkins_agent"
          port: 22
          sshHostKeyVerificationStrategy: "nonVerifyingKeyVerificationStrategy"
      name: "jenkins_agent"
      numExecutors: 2
      remoteFS: "/tmp"
      retentionStrategy: "always"

Here, we configure Jenkins using the configuration as code plugin:

Lines 1 to 12: Creation of a Jenkins credential of type SSH Username with private key with the private key.
Lines 13 to 25: We create the node configuration.

Start up

With all the configurations in place, it’s time to put everything into practice and start the environment. We’ll use the start.sh script to automate the execution of docker-compose (especially useful for repeated executions):

#!/bin/sh
work_path=$(pwd)
echo $work_path
sh $work_path/stop.sh

ssh-keygen -t rsa -f $work_path/ssh/jenkins_key -N "" -C ""

export JENKINS_AGENT_SSH_PUB=$(cat $work_path/ssh/jenkins_key.pub)
echo $JENKINS_AGENT_SSH_PUB
docker-compose up --build -d

In summary, the start.sh script:

Executes the stop.sh script to remove any existing environment.
Generates the ssh key for secure communication between the jenkins and ssh-agent containers.
Exports the environment variable JENKINS_AGENT_SSH_PUB.
Builds and starts the environment.

Conclusion

In this article, we explored some essential concepts for a robust Jenkins setup and then proceeded with the actual configuration.

Starting with the environment setup, we used the Dockerfile and docker-compose.yaml to define and orchestrate the environment’s services. We then configured Jenkins’ essential features, such as plugins and executors, using the plugins.txt and executors.groovy files.

Finally, we used a script (start.sh) to automate the execution of all these steps.

The final project will be available in the repository repo-link.

In future articles, we will add more steps and configurations for Jenkins. If you’re interested, stay tuned for updates.

Photo by Chilli Charlie on Unsplash

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