Building Docker Images with Jenkins

The Workflow

Typical CI/CD: build the jar → build an image → push to a registry → deploy. Jenkins has first-class Docker support.

Dockerfile in the Repo

FROM eclipse-temurin:21-jre
WORKDIR /app
COPY target/app-*.jar app.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "app.jar"]

Build and Push

pipeline {
    agent any
    environment {
        IMAGE = "docker.io/you/app"
        TAG = "1.0.${BUILD_NUMBER}"
    }
    stages {
        stage('Build jar') { steps { sh 'mvn -B clean package' } }
        stage('Build image') {
            steps {
                sh "docker build -t $IMAGE:$TAG ."
            }
        }
        stage('Push') {
            steps {
                withCredentials([string(credentialsId: 'dockerhub', variable: 'DOCKER_PASS')]) {
                    sh 'echo "$DOCKER_PASS" | docker login -u you --password-stdin'
                    sh "docker push $IMAGE:$TAG"
                }
            }
        }
    }
}

Docker inside Docker

When the agent is itself a container, mount the host socket carefully: -v /var/run/docker.sock:/var/run/docker.sock. For production prefer a dedicated Docker-in-Docker agent or shared socket workers, and never run builds as root.

Tagging Strategy

• Use unique tags per build: app:1.0.42 or the Git SHA.
• Promote a validated tag to latest only after tests pass.
• Keeps every release reproducible and rollback-friendly.

Key Points

• Images make releases immutable: what you tested is what runs.
• Sign in to the registry with injected credentials.
• Unique tags = auditable, reversible deploys.