19. Configuring Jenkins-Slave

The Udemy course Learn DevOps: CI/CD with Jenkins using Pipelines and Docker teaches how to work with Jenkins slaves. I had some problems with activating the Jenkins-slave container on a second system.



Activity 19.1: Configuring the Jenkins-slave

  • The system with the Jenkins-Master runs in a Docker container on Ubuntu 20.04.
  • Your second system with Jenkins-Slave runs as a Docker container on Ubuntu 20.04.
  • You have started the two computer.
  • You have the SSH keys available.

In this activity you will:

  1. Copy public key to slave.
  2. Create local SSH keys.
  3. Configure slave
  4. Create Jenkins-slave container
  5. On the Jenkins-master
Step 1: Copy public key to slave
1$ ssh-copy-id <user>@<ip-address slave>
2$ sudo chmod 666 /var/run/docker.sock
Step 2: Install Docker on slave
1$ sudo apt update
2$ sudo apt install docker.io
3$ sudo systemctl start docker
4$ sudo systemctl docker enable
5$ sudo groupadd docker
6$ sudo usermod -aG docker USER
7$ sudo reboot
Step 3: Configure slave
1$ mkdir -p /var/jenkins_home/.ssh
2$ cp /home/USER/.ssh/authorizedkeys /var/jenkinshome/.ssh
3$ sudo chmod 700 /var/jenkins_home/.ssh
4$ sudo chmod 600 /var/jenkinshome/.ssh/authorizedkeys
5$ sudo chown -R 1000:1000 /var/jenkins_home
6$ sudo chmod 666 /var/run/docker.sock
Step 4: Create Jenkins-slave container

Run the following docker command:

docker run -p 2222:22 \
  -v /var/jenkins_home:/var/jenkins_home \
  -v /var/run/docker.sock:/var/run/docker.sock \
  --restart always \
  -d wardviaene/jenkins-slave
Step 5: On the Jenkins-master
1$ ssh-keyscan -p 2222 <ip-address slave> >> /var/jenkinshome/.ssh/knownhosts


2$ docker exec -it jenkins bash
3$ ssh jenkins@<ip-address slave> -p 2222

Activity 19.2: Configuring the Jenkins Node

In Jenkins, select New node:

Name: Builder 2
# of executers: 2 
Remote root directory: /var/jenkins_home
Labels: builder2
Use: Only build jobs with label expressions matching this node
Output method:
 Launch agent via SSH
 Host: <ip-address Jenkins slave>
 Credentials: #1
 Host Key Verifications Strategy:
   Select 'Require manual verification of initial connection' #2

#1 Create an account with the name jenkins and past the your private key in the field (cat rsa-id.pub)

#2 The first time you will see the message ??? appears in the menu, click on it.