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      How To Install Jenkins on Kubernetes


      The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program.

      Introduction

      Continuous Integration/Continuous Deployment (CI/CD) pipelines are one of the core components of the DevOps environment. They help streamline the workflow between multiple teams and increase productivity. Jenkins is a widely-used open source automation server that can set up CI/CD pipelines.

      In this tutorial, you will install Jenkins on Kubernetes. You will then access the Jenkins UI and run a sample pipeline.

      Prerequisites

      To follow this tutorial, you will need:

      Step 1 — Installing Jenkins on Kubernetes

      Kubernetes has a declarative API and you can convey the desired state using either a YAML or JSON file. For this tutorial, you will use a YAML file to deploy Jenkins. Make sure you have the kubectl command configured for the cluster.

      First, use kubectl to create the Jenkins namespace:

      • kubectl create namespace jenkins

      Next, create the YAML file that will deploy Jenkins.

      Create and open a new file called jenkins.yaml using nano or your preferred editor:

      Now add the following code to define the Jenkins image, its port, and several more configurations:

      jenkins.yaml

      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: jenkins
      spec:
        replicas: 1
        selector:
          matchLabels:
            app: jenkins
        template:
          metadata:
            labels:
              app: jenkins
          spec:
            containers:
            - name: jenkins
              image: jenkins/jenkins:lts
              ports:
                - name: http-port
                  containerPort: 8080
                - name: jnlp-port
                  containerPort: 50000
              volumeMounts:
                - name: jenkins-vol
                  mountPath: /var/jenkins_vol
            volumes:
              - name: jenkins-vol
                emptyDir: {}
      

      This YAML file creates a deployment using the Jenkins LTS image and also opens port 8080 and 50000. You use these ports to access Jenkins and accept connections from Jenkins workers respectively.

      Now create this deployment in the jenkins namespace:

      • kubectl create -f jenkins.yaml --namespace jenkins

      Give the cluster a few minutes to pull the Jenkins image and get the Jenkins pod running.

      Use kubectl to verify the pod’s state:

      • kubectl get pods -n jenkins

      You will receive an output like this:

      NAME                       READY   STATUS    RESTARTS   AGE
      jenkins-6fb994cfc5-twnvn   1/1     Running   0          95s
      

      Note that the pod name will be different in your environment.

      Once the pod is running, you need to expose it using a Service. You will use the NodePort Service type for this tutorial. Also, you will create a ClusterIP type service for workers to connect to Jenkins.

      Create and open a new file called jenkins-service.yaml:

      • nano jenkins-service.yaml

      Add the following code to define the NodePort Service:

      jenkins-service.yaml

      apiVersion: v1
      kind: Service
      metadata:
        name: jenkins
      spec:
        type: NodePort
        ports:
          - port: 8080
            targetPort: 8080
            nodePort: 30000
        selector:
          app: jenkins
      
      ---
      
      apiVersion: v1
      kind: Service
      metadata:
        name: jenkins-jnlp
      spec:
        type: ClusterIP
        ports:
          - port: 50000
            targetPort: 50000
        selector:
          app: jenkins
      

      In the above YAML file, you define your NodePort Service and then expose port 8080 of the Jenkins pod to port 30000.

      Now create the Service in the same namespace:

      • kubectl create -f jenkins-service.yaml --namespace jenkins

      Check that the Service is running:

      • kubectl get services --namespace jenkins

      You will receive an output like this:

      Output

      NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE jenkins NodePort your_cluster_ip <none> 8080:30000/TCP 15d

      With NodePort and Jenkins operational, you are ready to access the Jenkins UI and begin exploring it.

      Step 2 — Accessing the Jenkins UI

      In this step, you will access and explore the Jenkins UI. Your NodePort service is accessible on port 30000 across the cluster nodes. You need to retrieve a node IP to access the Jenkins UI.

      Use kubectl to retrieve your node IPs:

      • kubectl get nodes -o wide

      kubectl will produce an output with your external IPs:

      Output

      NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME your_node Ready <none> 16d v1.18.8 your_internal_ip your_external_ip Debian GNU/Linux 10 (buster) 4.19.0-10-cloud-amd64 docker://18.9.9 your_node Ready <none> 16d v1.18.8 your_internal_ip your_external_ip Debian GNU/Linux 10 (buster) 4.19.0-10-cloud-amd64 docker://18.9.9 your_node Ready <none> 16d v1.18.8 your_internal_ip your_external_ip Debian GNU/Linux 10 (buster) 4.19.0-10-cloud-amd64 docker://18.9.9

      Copy one of the your_external_ip values.

      Now open a web browser and navigate to http://your_external_ip:30000.

      A page will appear asking for an administrator password and instructions on retrieving this password from the Jenkins Pod logs.

      Let’s use kubectl to pull the password from those logs.

      First, return to your terminal and retrieve your Pod name:

      • kubectl get pods -n jenkins

      You will receive an output like this:

      NAME                       READY   STATUS    RESTARTS   AGE
      jenkins-6fb994cfc5-twnvn   1/1     Running   0          9m54s
      

      Next, check the Pod’s logs for the admin password. Replace the highlighted section with your pod name:

      • kubectl logs jenkins-6fb994cfc5-twnvn -n jenkins

      You might need to scroll up or down to find the password:

      Running from: /usr/share/jenkins/jenkins.war
      webroot: EnvVars.masterEnvVars.get("JENKINS_HOME")
      . . .
      
      Jenkins initial setup is required. An admin user has been created and a password generated.
      Please use the following password to proceed to installation:
      
      your_jenkins_password
      
      This may also be found at: /var/jenkins_home/secrets/initialAdminPassword
      . . .
      

      Copy your_jenkins_password. Now return to your browser and paste it into the Jenkins UI.

      Once you enter the password, Jenkins will prompt you to install plugins. Because you are not doing anything unusual, select Install suggested plugins.

      After installation, Jenkins will load a new page and ask you to create an admin user. Fill out the fields, or skip this step by pressing the skip and continue as admin link. This will leave your username as admin and your password as your_jenkins_password.

      Another screen will appear asking about instance configuration. Click the Not now link and continue.

      After this, Jenkins will create a summary of your choices and print Jenkins is ready! Click on start using Jenkins and the Jenkins home page will appear.

      jenkins wizard

      Now that you have installed and configured Jenkins on your cluster let’s demonstrate its capabilities and run a sample pipeline.

      Step 3 — Running a Sample Pipeline

      Jenkins excels at creating pipelines and managing CI/CD workflows. In this step we will build one of Jenkins’ sample pipelines.

      From the Jenkins home page, click on the New item link on the left-hand menu.

      A new page will appear. Choose Pipeline and press OK.

      jenkins wizard

      Jenkins will redirect you to the pipeline’s configuration. Find the Pipeline section and select Hello World from the try sample pipeline dropdown menu. This menu appears on the right-hand side. After selecting Hello World, click the Save button.

      jenkins wizard

      Jenkins will redirect you to the pipeline home page. Click on build now from the left-hand menu and watch the pipeline begin to run. The #1 signifies that this is the first build. Once the task completes, you will see some stats about the build.

      jenkins wizard

      You can also check the console output to see what happened while the pipeline was running. Hover over #1 and a dropdown menu will appear. Choose console output to view the build’s details.

      Your Hello World pipeline is not very sophisticated, but it does demonstrate just how well Jenkins can create and manage CI/CD workflows.

      Conclusion

      In this tutorial, you installed and configured Jenkins on a Kubernetes cluster and then you ran a sample pipeline. Jenkins has a large repository of plugins that can help you perform very complex operations. You can also add your GitHub repositories, multiple types of worker instances, and more. To learn more about using Jenkins, explore the official Jenkins documentation.



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