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jenkins controller agent

Prerequisites​

  • System: Two Ubuntu servers with root or sudo access and network connectivity
    • controller-server: 192.168.64.10
    • agent-server: 192.168.64.11

Step 1: Install Java (Both Servers)​

Jenkins requires a Java Runtime Environment (JRE) to run. We will install the OpenJDK package

On controller

sudo apt update
sudo apt install openjdk-17-jdk -y

java -version

On agent

sudo apt update
sudo apt install openjdk-17-jdk -y

java --version

sudo systemctl status ssh

Step 2: Install Jenkins (Controller Server)​

Add Jenkins repository

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

Update package list and install Jenkins

sudo apt-get update
sudo apt-get install jenkins -y

Start and enable Jenkins service

sudo systemctl start jenkins
sudo systemctl enable jenkins
sudo systemctl status jenkins

Initial Jenkins setup

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

Step 3: Generate SSH Key Pair (Controller Server)​

Configure SSH key

  • Controller stores the private key
  • Agent stores the public key
sudo su - jenkins

ssh-keygen -t rsa -b 4096

cat ~/.ssh/id_rsa.pub

Step 4: Add Public Key (Agent Server)​

Ensure SSH directory and authorized_keys file exist with correct permissions

mkdir -p ~/.ssh
chmod 700 ~/.ssh
touch ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

Add the public key

vim ~/.ssh/authorized_keys

Step 5: Configure Agent Node (Controller Server)​

Retrieve the private key

sudo cat /var/lib/jenkins/.ssh/id_rsa

Add SSH credentials in Jenkins UI

  • SSH Username with private key
    • ID: agent-ssh-key
    • Description: SSH key for agent-server
    • Username: ubuntu
    • Private key: ...

Add new node

  • Node name: ubuntu-agent-1
  • Description: Ubuntu Agent VM
  • Number of executors: 1
  • Remote root directory: /home/ubuntu/jenkins-agent-ubuntu
  • Labels; ubuntu agent
  • Launch method: Launch agents via SSH
    • Host: 192.168.64.11
    • Credentials: ubuntu (SSH key for agent-server)

Step 5: Test With a Job​

Freestyle project

  • Restrict where this project can be run
    • Label expression: ubuntu
  • Build steps
    • Execute shell
echo "Hello from Jenkins Agent!"
echo "Running on host: $(hostname)"
echo "Workspace directory: $(pwd)"
echo "Java version on agent:"
java -version
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