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.

UNDER DEVELOPMENT

19. Configuring Jenkins-Slave

Activity 19.1: Configuring the Jenkins-slave
Activity 19.2: Configuring the Jenkins Node

Activity 19.1: Configuring the Jenkins-slave

Prerequisites

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:

Copy public key to slave.
Create local SSH keys.
Configure slave
Create Jenkins-slave container
On the Jenkins-master

Step 1: Copy public key to slave

Step	Action	Comment
1	$ ssh-copy-id <user>@<ip-address slave>
2	$ sudo chmod 666 /var/run/docker.sock

Step 2: Install Docker on slave

Step	Action	Comment
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

Step	Action	Comment
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

Step	Action	Comment
1	$ ssh-keyscan -p 2222 <ip-address slave> >> /var/jenkinshome/.ssh/knownhosts

Test:

Step	Action	Comment
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.