How to simply build a Jenkins server and Agent

Having been working on another DevOps Academy it was surprising with the research that the students did on how to build a Jenkins server with Agent, how complicated most people made it.

This example is based on using AWS with 2 EC2 instances, but would work on-prem and other clouds.

Steps to build

1. Create 2 Ubuntu instances both Medium

• 1 is Controller
• 1 is the Agent
• Settings
• t2.medium
• 20GB disk
• Ubuntu image
• Select or create a security group (e.g. jenkinssg) that has the following inbound ports
• 8080
• 22
• 8200

2. Install Jenkins on the controller

• ssh onto the Jenkins controller
• sudo apt update # It's Ubunutu after all
• sudo apt -y install openjdk-11-jdk # Install Java, Jenkins needs it
• wget -q -O - https://pkg.jenkins.io/debian/jenkins.io.key | sudo apt-key add -
• sudo sh -c 'echo deb http://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'
• sudo apt update
• sudo apt install jenkins
• sudo cat /var/lib/jenkins/secrets/initialAdminPassword   # Get the login password

3. Web browser

• Point your web browser at http://yourPublicIPforInstance:8080
• Paste in the text from the file
• Click Continue button
• Click Install suggested plugins
• Fill in the form to create the main Jenkins user
• Username: admin
• Password: secret123
• Confirm password: secret123
• Fullname: Administrator
• E-mail address: root@nowhere.com
• Click Save and Continue button
• Change the IP address to the Private IP address of your Jenkins instance
• Leave the http:// and the :8080/
• Click Save and Finish button
• Click Start using Jenkins button

4. Configuring Jenkins to see the new node to be the agent

• After doing step 3 you should be logged in as Administrator
• If not log in using admin and the password you set
• Click Manage Jenkins in the left menu
• Click Manage Nodes and Clients
• Click New Node in the new menu
• Set the Node name to Worker1
• Select Permanent Agent
• Click Create button
• New screen
• Number of executors: 2
• Remote root directory: /home/ubuntu
• Labels: all
• Leave all other as default
• Click Save
• The worker node will show as not connected
• Click on Worker1 link
• You'll notice an error message
• JNLP agent port is disabled and agents cannot connect this way. Go to security configuration screen and change it.
• Click the link Go to security configuration screen and change it.
• Scroll down to Agents
• Select Fixed
• Set the Port to 8200 (This is already allowed by jenkinssg)
• Scroll to the bottom and click the Save button
• Click Manage Nodes and Clients
• Click Worker1
• Right click the blue agent.jar link and Copy link address

5. Now ssh on to your Worker/Agent instance

• sudo apt update
• sudo apt -y install openjdk-11-jdk
• wget http://52.213.211.75:8080/jnlpJars/agent.jar
• Where the http:// link is pasted from the Copy link address
• On the Jenkins web page copy the 2nd box echo line
• Paste this line into the terminal of the Worker/Agent ssh session
• On the Jenkins web page copy the 2nd box java -jar line
• In the terminal of the Worker/Agent ssh session
• Type the word   nohup
• Then paste the java -jar line after this
• Type a space and then   &    at the end of the line
• e.g.
• nohup java -jar agent.jar -jnlpUrl http://172.31.16.36:8080/computer/Worker1/jenkins-agent.jnlp -secret @secret-file -workDir "/home/ubuntu" &

6. Back to the Jenkins web site

• Click Back to List if you are in the Agent Worker1 screen
• or
• Click Dashboards top left of the page
• Click Manage Jenkins
• Click Manage Nodes and Clouds
• Note your agent is now connected

NOTE:

This configuration doesn't create a service to start the agent on reboot, but is purely an example to get it running.  To make the agent a proper service you would need to create the appropriate file in /etc/systemd/system (call it jenkins-agent.service) or for older systems the service script in /etc/init.d.