Jenkins

What is Jenkins?

Jenkins is an open-source automation server widely used to automate parts of the software development lifecycle. It is primarily used for continuous integration (CI) and continuous delivery (CD), enabling developers to automatically build, test, and deploy applications.

Jenkins supports hundreds of plugins to integrate with virtually every tool in the software development ecosystem, making it highly customisable and adaptable to various workflows. Jenkins can manage and monitor builds, trigger automated testing, and push changes to production without manual intervention, significantly improving development speed and reliability.

Key Features:

Extensive Plugin Ecosystem – Integrates with tools like Git, Docker, Kubernetes, Maven, and more.
Pipeline as Code – Enables the definition of build and deployment pipelines through Jenkinsfiles.
Scalability – Can distribute workloads across multiple machines to handle large builds and tests.
Extensible – Custom plugins allow for integration with numerous other tools, enabling a highly flexible CI/CD workflow.

Prerequsites

Virtual Machine running Ubuntu 22.04 or newer

Update Package Repository and Upgrade Packages

sudo apt update
sudo apt upgrade

Become root

sudo -i

Adoptium Java 17

Add Adoptium repository

wget -O - https://packages.adoptium.net/artifactory/api/gpg/key/public | tee /etc/apt/keyrings/adoptium.asc
echo "deb [signed-by=/etc/apt/keyrings/adoptium.asc] https://packages.adoptium.net/artifactory/deb $(awk -F= '/^VERSION_CODENAME/{print$2}' /etc/os-release) main" | tee /etc/apt/sources.list.d/adoptium.list

Install Java 17

Update repository and install Java

apt update
apt install temurin-17-jdk
/usr/bin/java --version
exit

Install Jenkins

sudo wget -O /usr/share/keyrings/jenkins-keyring.asc \
  https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key
echo "deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc]" \
  https://pkg.jenkins.io/debian-stable binary/ | sudo tee \
  /etc/apt/sources.list.d/jenkins.list > /dev/null
sudo apt-get update
sudo apt-get -y install jenkins

Start Jenkins

sudo systemctl daemon-reload
sudo systemctl enable jenkins
sudo systemctl start jenkins
sudo systemctl status jenkins

Print initial admin password

sudo cat /var/lib/jenkins/secrets/initialAdminPassword

Copy Temporary password

`Firewall Settings if required`

YOURPORT=8080
PERM="--permanent"
SERV="$PERM --service=jenkins"
firewall-cmd $PERM --new-service=jenkins
firewall-cmd $SERV --set-short="Jenkins ports"
firewall-cmd $SERV --set-description="Jenkins port exceptions"
firewall-cmd $SERV --add-port=$YOURPORT/tcp
firewall-cmd $PERM --add-service=jenkins
firewall-cmd --zone=public --add-service=http --permanent
firewall-cmd --reload

Enable TLS

Install Nginx

sudo apt install -y nginx

sudo systemctl enable nginx
sudo systemctl start nginx
sudo systemctl status nginx

Configure Nginx reverse proxy

sudo vim /etc/nginx/sites-available/jenkins.devopsfoundry.com

upstream jenkins {
    server 127.0.0.1:8080;
}
server {
    listen      80;
    server_name jenkins.devopsfoundry.com;
    access_log  /var/log/nginx/jenkins.access.log;
    error_log   /var/log/nginx/jenkins.error.log;
    proxy_buffers 16 64k;
    proxy_buffer_size 128k;
    location / {
        proxy_pass  http://jenkins;
        proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
        proxy_redirect off;
        proxy_set_header    Host            $host;
        proxy_set_header    X-Real-IP       $remote_addr;
        proxy_set_header    X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header    X-Forwarded-Proto https;
    }
}

sudo ln -s /etc/nginx/sites-available/jenkins.devopsfoundry.com /etc/nginx/sites-enabled/

sudo nginx -t
sudo systemctl restart nginx

Install Certbot and obtain SSL certificate

sudo apt install -y certbot python3-certbot-nginx
sudo certbot --nginx -d jenkins.devopsfoundry.com

Cloudflare Tunnel Config

tunnel: j-tunnel
credentials-file: /home/jenkins/.cloudflared/3e9dfb6f-63c9-4902-b48d-83aa2abb386a.json

ingress:
  - hostname: jenkins.devopsfoundry.com
    service: http://127.0.0.1:8080  # Another service using HTTP
  - service: http_status:404  # Default for unmatched requests

Sample Jenkinsfile

pipeline {
    agent any
    stages {
        stage('Hello World') {
            steps {
                echo 'Hello World'
            }
        }
    }
}

Setup Jenkins Agent

Run the following commands on your Jenkins agent node:

sudo adduser jenkins
sudo usermod -aG sudo jenkins
sudo apt install -y fontconfig openjdk-17-jre

Grant admin user passwordless sudo access

sudo visudo

jenkins ALL=(ALL) NOPASSWD:ALL

Generate SSH key pair on Jenkins-UI/Master server

ssh-keygen -t rsa -b 4096 -C "jenkins-agent"

Copy the public key to the Jenkins agent

ssh-copy-id jenkins@<agent-ip-address>

Enter password for Jenkins-agent if prompted

Ensure SSH key-based authentication works, then logout

ssh jenkins@<agent-ip-address>

Configure known hosts for Jenkins-UI Complete this on UI

sudo mkdir -p /var/lib/jenkins/.ssh/

Change permission for known_hosts

sudo chown -R jenkins:jenkins /var/lib/jenkins/.ssh

sudo ssh-keyscan -H <agent-ip-address> >> /var/lib/jenkins/.ssh/known_hosts

Create Jenkins credential with SSH username with private Key

Add private key directly

cat jenkinsAgent_rsa.pub >> ~/.ssh/authorized_keys

Ensure that the permissions of the ~/.ssh directory is secure, as most ssh daemons will refuse to use keys that have file permissions that are considered insecure:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys ~/.ssh/jenkinsAgent_rsa

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