Jenkins Master/Slave Setup

In this article we will learn how to setup Devops tool Jenkins in master/slave mode.

With the growing popularity of Microservices, it is becoming necessary for any company to develop and launch several services at the same time. It's at this point that the CI tools must provide a way for sharing the load across several machines/servers.

Jenkins also has the capability of distributing build jobs across a large number of systems, which is known as Jenkins distributed builds. We can set up a farm of build servers using Jenkins to distribute the burden or perform the build jobs in different settings.

When we have a large project to build and the load has to be distributed across several machines on the network, distributed builds improve?the efficiency of the build process. Jenkins implements the Master/Slave architecture to manage distributed builds.

We may associate a project with the slave node and then schedule it for the build when we've created and configured it.

Jenkins Master is the primary Jenkins server and is responsible for the following tasks:

• It distributes the builds among the numerous slaves for execution.
• It organises the build projects.
• It keeps an eye on the slaves at all times.
• Master can also run build jobs directly if necessary.
• It keeps track of the build outcomes and shows them.

Jenkins Slave runs on a remote machine. A slave is responsible for the following tasks:

• Slaves can be operated on a number of different operating systems.
• It responds to the Jenkins Master's demands.
• Apart from the fact that Jenkins executes the build task on the next available save,?
• we can always arrange the project to run on a certain sort of slave computer.
• It also completes construction operations that the Master has dispatched.

Steps -

1. Install Java on master node

2. Install Jenkins on master node

3. Install java on slave node

4. Create a user and ssh keys on slave node

5. Copy keys on master node

6. Join slave node to master

7. Test the setup

Procedure -

1. Install java on master node

[root@jenkins-master ~]# dnf install java-11-openjdk -y
        

2. Install jenkins on master node

[root@jenkins-master ~]# dnf install wget -y


[root@jenkins-master ~]# wget -O /etc/yum.repos.d/jenkins.repo? https://pkg.jenkins.io/redhat-stable/jenkins.repo


[root@jenkins-master ~]# rpm --import https://pkg.jenkins.io/redhat-stable/jenkins.io.key


[root@jenkins-master ~]# dnf install jenkins -y


[root@jenkins-master ~]# systemctl status jenkins


[root@jenkins-master ~]# systemctl enable --now? jenkins


[root@jenkins-master ~]# systemctl status jenkins


[root@jenkins-master ~]# firewall-cmd --permanent --add-port=8080/tcp


[root@jenkins-master ~]# firewall-cmd --reload
        

Access URL https://192.168.0.103:8080

We will be asked to enter the password, like below -

When prompted get the password from below location and enter it -

[root@jenkins-master ~]# cat /var/lib/jenkins/secrets/initialAdminPassword

8913aa206f044edb83ca0ddf52cbe085

Install the select the suggested plugins        

On next screen you can see its asking to install the suggested plugins -

On next screen you will be prompted to create Jenkins user -

Installation is completed

We get default Jenkins Dashboard

3. Install java on slave node

[root@jenkins-slave1 ~]# dnf install java-11-openjdk -y
        

4. Create a user and ssh keys on slave node

[root@jenkins-slave1 ~]#?useradd prayag
        

Generate ssh-key for user prayag and note down private key - to be added in Jenkins credentials -

[prayag@jenkins-slave ~]$ ssh-keygen -t rsa

[prayag@jenkins-slave ~]$ cd .ssh/

[prayag@jenkins-slave ~]$ cat id_rsa.pub > authorized_keys

[prayag@jenkins-slave ~]$ chmod 700 authorized_keys

[prayag@jenkins-slave ~]$ cat authorized_keys        

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5. Copy keys on master node

On master - copy public key in /var/lib/jenkins/.ssh/known_hosts - used when selecting option Know hosts key strategy

[root@jenkins-master ~]# mkdir /var/lib/jenkins/.ss

[root@jenkins-master ~]# chown jenkins:jenkins /var/lib/jenkins/.ssh

[root@jenkins-master ~]# echo "ssh-rsa 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 [email protected]" > /var/lib/jenkins/.ssh/known_hosts

[root@jenkins-master ~]# cat /var/lib/jenkins/.ssh/known_hosts

ssh-rsa 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 [email protected]

[root@jenkins-master ~]# ssh-keyscan -H jenkins-slave.example.com >>/var/lib/jenkins/.ssh/known_hostsh        

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6. Join slave node to master

To join the Jenkins slave node to Jenkins Master, perform below steps -

Select Build Executor Status > New Node > Type - Permanent?

Select below values -

Name - jenkins-slave1

Description - jenkins-slave1

Number of executors - 1?

Remote root directory - /home/prayag

Labels - jenkins-slave1

Usage - Use this mode as much as possible

Launch method - Launch agents via SSH

Host - 192.168.0.103

Credentials - use ssh username / private key options

Host Key Verification Strategy - Know hosts key strategy

Save and check that new slave node is added and is in sync

When prompted give node name

Select Permanent Agent

Create ssh credentials with Private key -

Enter node name and select Permanent Agent

We can see Jenkins Slave is launching ..

Agent status - "is being launched"

Jenkins Slave node is now is "In Sync"

7. Test Jenkins Jobs -

• Create "new item"
• Enter an item name – Job1

Chose Freestyle project

• Under General Section

Choose Restrict where this project can be run

Update your jenkins slave label jenkins-slave1

• Under Build section Execute shell

 #!/bin/bash
 echo "Testing Jenkins Master Slave Setup"
        

• Save your job
• Build job
• Check "console output"

Create new item and in General tab - select "Restrict where this project can be run"

Select Build as "Execute shell" and run echo command - "Testing Jenkins Master Slave Setup"

Save and run build - "Build Now"

Once the build is completed we can check the console output - "Building remotely jenkins-slave1" in workspace....

I hope you found this article to be useful in some way. I'll be back with some more interesting new articles on DEVOPS tools.