KodeKloud Notes

In this hands-on guide, you’ll use a Jenkins Pipeline to build a Spring Boot JAR with Maven, run unit tests, then build and push a Docker image to Docker Hub, tagging it with the Git commit SHA.

Pipeline Stages

Stage	Purpose
Build Artifact – Maven	Compile code and package the JAR
Unit Tests – JUnit & JaCoCo	Execute tests and collect coverage
Docker Build & Push	Build Docker image, tag with `$GIT_COMMIT`, and push

Dockerfile

Include this Dockerfile at the repo root to define your container:

FROM openjdk:8-jdk-alpine
EXPOSE 8080
ARG JAR_FILE=target/*.jar
ADD ${JAR_FILE} app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

This:

Starts from the lightweight openjdk:8-jdk-alpine image
Exposes port 8080 (Spring Boot default)
Adds the JAR built by Maven
Runs the JAR on container start

Initial Jenkinsfile

Add a Docker Build & Push stage after Maven build and unit tests:

pipeline {
    agent any

    stages {
        stage('Build Artifact - Maven') {
            steps {
                sh 'mvn clean package -DskipTests=true'
                archive 'target/*.jar'
            }
        }

        stage('Unit Tests - JUnit and Jacoco') {
            steps {
                sh 'mvn test'
            }
            post {
                always {
                    junit 'target/surefire-reports/*.xml'
                    jacoco execPattern: 'target/jacoco.exec'
                }
            }
        }

        stage('Docker Build and Push') {
            steps {
                sh 'printenv'
                sh 'docker build -t siddharth67/numeric-app:"$GIT_COMMIT" .'
                sh 'docker push siddharth67/numeric-app:"$GIT_COMMIT"'
            }
        }
    }
}

Note

printenv lists all Jenkins environment variables. We leverage $GIT_COMMIT to tag images uniquely.

Inspecting Images on the Jenkins VM

On the VM where Docker runs, list existing images:

root@devsecops-cloud:~$ docker images
REPOSITORY                             TAG        IMAGE ID      CREATED         SIZE
weaveworks/weave-npc                  latest     d1a364dc548d  2 weeks ago     133MB
weaveworks/weave-kube                 2.8.1      f792d56d4ff  6 months ago    39.3MB
k8s.gcr.io/kube-proxy                 v1.20.0    df29c2434e6  6 months ago    89MB
...

Trigger the pipeline. The Docker Build step succeeds but the Push fails:

Successfully built c2552997972a
Successfully tagged siddharth67/numeric-app:936d67ea8d593e435dcdf8878fef8578c71c886
The push refers to repository [docker.io/siddharth67/numeric-app]
denied: requested access to the resource is denied

Warning

Push failure means Jenkins doesn’t have Docker Hub credentials configured.

Configuring Docker Hub Credentials in Jenkins

Ensure the Docker Pipeline plugin is installed:

The image shows the Jenkins Plugin Manager interface with a list of installed plugins, including Docker-related plugins. A search for "docker" is highlighted, and various plugins are listed with options to uninstall.

Then add Docker Hub credentials:

Go to Manage Jenkins → Manage Credentials → Global → Add Credentials
Select Username with password
Enter your Docker Hub username & password
Set an ID (e.g., docker-hub) and save

The image shows a Jenkins interface displaying the "Global credentials (unrestricted)" section, with a credential named "kubeconfig" listed as a secret file.

The image shows a Jenkins interface where a user is adding global credentials, including a username, password, and ID. The browser tabs and taskbar are also visible.

Updated Jenkinsfile

Wrap Docker commands in withDockerRegistry, referencing the credential ID:

pipeline {
    agent any

    stages {
        stage('Build Artifact - Maven') {
            steps {
                sh 'mvn clean package -DskipTests=true'
                archive 'target/*.jar'
            }
        }

        stage('Unit Tests - JUnit and Jacoco') {
            steps {
                sh 'mvn test'
            }
            post {
                always {
                    junit 'target/surefire-reports/*.xml'
                    jacoco execPattern: 'target/jacoco.exec'
                }
            }
        }

        stage('Docker Build and Push') {
            steps {
                withDockerRegistry(credentialsId: 'docker-hub', url: '') {
                    sh 'docker build -t siddharth67/numeric-app:"$GIT_COMMIT" .'
                    sh 'docker push siddharth67/numeric-app:"$GIT_COMMIT"'
                }
            }
        }
    }
}

Note

An empty url defaults to Docker Hub. Make sure credentialsId matches the ID you created.

Verifying Build & Push

Re-run the pipeline. You should see:

# Shell Script - docker build -t siddharth67/numeric-app="$GIT_COMMIT"  # (self time 9s)
# Shell Script - docker push siddharth67/numeric-app="$GIT_COMMIT"      # (self time 310ms)

List images again to confirm the new tags:

root@devsecops-cloud:~$ docker images
REPOSITORY                       TAG                                 IMAGE ID        CREATED          SIZE
siddharth67/numeric-app         8be376a2279c6b3d924c62779a9e90c71   a014560b0908    32 seconds ago   122MB
siddharth67/numeric-app         93d6e7e8ad593a435bcdf8787b7fe8f5   c52599977e7a    4 minutes ago    122MB
nginx                           latest                              d1a364dc548d    2 weeks ago      133MB
...

You’ve now successfully built and pushed your Docker image. Next, integrate deployment to your Kubernetes cluster via the Jenkins Pipeline.

Demo Docker Build and Push