Docker image as artifact in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Jenkins pipeline snippet?

Consider this Jenkins pipeline step that builds a Docker image and tags it:

stage('Build Docker Image') {
  steps {
    script {
      dockerImage = docker.build("myapp:${env.BUILD_NUMBER}")
      echo dockerImage.id
    }
  }
}

What will be printed by echo dockerImage.id?

Jenkins

stage('Build Docker Image') {
  steps {
    script {
      dockerImage = docker.build("myapp:${env.BUILD_NUMBER}")
      echo dockerImage.id
    }
  }
}

A An error because dockerImage.id is not defined

B The string 'myapp:${env.BUILD_NUMBER}' literally

C The Jenkins build number only

D The unique image ID hash of the built Docker image

💡 Hint

Think about what docker.build() returns and what id represents.

The docker.build() method returns a Docker image object. The id property is the unique hash ID of the built image, which Jenkins can print.

🔀 Workflow

intermediate

Which Jenkins pipeline step correctly pushes a Docker image as an artifact to Docker Hub?

You have built a Docker image in Jenkins with tag myapp:${env.BUILD_NUMBER}. Which step correctly pushes this image to Docker Hub?

A sh 'docker push myapp:${env.BUILD_NUMBER}'

B docker.withRegistry('https://registry.hub.docker.com', 'dockerhub-credentials') { dockerImage.push() }

C docker.push('myapp:${env.BUILD_NUMBER}')

D dockerImage.push('latest')

💡 Hint

Remember Jenkins needs to authenticate to Docker Hub before pushing.

docker.withRegistry() wraps the push command with authentication. Calling dockerImage.push() inside it pushes the tagged image correctly.

❓ Troubleshoot

advanced

Why does this Jenkins pipeline fail to push the Docker image?

Given this snippet:

stage('Push Image') {
  steps {
    script {
      dockerImage = docker.build("myapp:${env.BUILD_NUMBER}")
      dockerImage.push()
    }
  }
}

The pipeline fails with an authentication error. What is the most likely cause?

A Missing <code>docker.withRegistry</code> block to provide Docker Hub credentials

B The image tag is invalid and causes push failure

C The <code>docker.build</code> command did not complete successfully

D The Jenkins agent does not have Docker installed

💡 Hint

Think about how Jenkins authenticates to Docker registries.

Without docker.withRegistry and credentials, Jenkins cannot authenticate to Docker Hub, causing push to fail.

🧠 Conceptual

advanced

What is the main benefit of using Docker images as artifacts in Jenkins pipelines?

Why do DevOps teams prefer storing Docker images as build artifacts in Jenkins pipelines?

A It ensures consistent deployment by using the exact same image built and tested

B It reduces the size of the Jenkins workspace by deleting source code

C It speeds up the Jenkins build by skipping tests

D It allows Jenkins to run containers without Docker installed on agents

💡 Hint

Think about consistency and reliability in deployments.

Storing Docker images as artifacts ensures the same tested image is deployed, avoiding differences between build and production.

✅ Best Practice

expert

Which Jenkinsfile snippet follows best practices for building, tagging, and pushing a Docker image as an artifact?

Choose the Jenkins pipeline snippet that correctly builds a Docker image, tags it with the build number and 'latest', pushes both tags to Docker Hub, and uses credentials securely.

A

stage('Build and Push') {
  steps {
    script {
      dockerImage = docker.build("myapp:${env.BUILD_NUMBER}")
      dockerImage.push('latest')
      dockerImage.push()
    }
  }
}

B

stage('Build and Push') {
  steps {
    sh 'docker build -t myapp:${env.BUILD_NUMBER} .'
    sh 'docker push myapp:${env.BUILD_NUMBER}'
    sh 'docker push myapp:latest'
  }
}

C

stage('Build and Push') {
  steps {
    script {
      dockerImage = docker.build("myapp:${env.BUILD_NUMBER}")
      docker.withRegistry('https://registry.hub.docker.com', 'dockerhub-credentials') {
        dockerImage.push()
        dockerImage.push('latest')
      }
    }
  }
}

D

stage('Build and Push') {
  steps {
    script {
      dockerImage = docker.build("myapp:latest")
      dockerImage.push()
      dockerImage.push('${env.BUILD_NUMBER}')
    }
  }
}

💡 Hint

Look for correct tag usage, push order, and secure credential handling.

Option C builds with the build number tag, pushes that tag and 'latest' inside a docker.withRegistry block using credentials. This is the recommended secure and clear approach.