Building Docker images in pipeline in Jenkins - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the Docker build step in a Jenkins pipeline.

Jenkins

stage('Build Docker Image') {
  steps {
    script {
      dockerImage = docker.[1]('myapp:latest')
    }
  }
}

Drag options to blanks, or click blank then click option'

Abuild

Bpull

Crun

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' instead of 'build' will try to run a container, not build an image.

Using 'push' before building the image will cause an error.

The docker.build command builds a Docker image from the Dockerfile in the workspace.

2fill in blank

medium

Complete the code to push the built Docker image to a registry in the Jenkins pipeline.

Jenkins

stage('Push Docker Image') {
  steps {
    script {
      dockerImage.[1]()
    }
  }
}

Drag options to blanks, or click blank then click option'

Apull

Bbuild

Cpush

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' here will try to build again instead of pushing.

Using 'pull' will try to download an image, not upload.

The push method uploads the Docker image to the specified registry.

3fill in blank

hard

Fix the error in the Jenkins pipeline code to correctly build a Docker image with a custom Dockerfile path.

Jenkins

stage('Build Custom Docker Image') {
  steps {
    script {
      dockerImage = docker.[1]('myapp:custom', '-f Dockerfile.custom .')
    }
  }
}

Drag options to blanks, or click blank then click option'

Arun

Bbuild

Cpush

Dpull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' will try to start a container instead of building.

Using 'push' will try to upload an image that may not exist yet.

The build method accepts the image name and build arguments like the Dockerfile path.

4fill in blank

hard

Fill both blanks to build and push a Docker image with a tag in a Jenkins pipeline.

Jenkins

stage('Build and Push') {
  steps {
    script {
      dockerImage = docker.[1]('myapp:[2]')
      dockerImage.push()
    }
  }
}

Drag options to blanks, or click blank then click option'

Abuild

Blatest

Cdev

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' instead of 'build' will cause an error.

Using 'latest' tag when you want a development version.

Use build to create the image and dev as the tag for development version.

5fill in blank

hard

Fill all three blanks to build a Docker image, tag it, and push it to a registry in a Jenkins pipeline.

Jenkins

stage('Build, Tag, and Push') {
  steps {
    script {
      dockerImage = docker.[1]('myapp:[2]')
      dockerImage.[3]('myregistry.com/myapp:[2]')
    }
  }
}

Drag options to blanks, or click blank then click option'

Abuild

Bpush

Ctag

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of build, tag, and push.

Using 'run' instead of 'tag' or 'push'.

First, build creates the image. Then tag adds a registry tag. Finally, push uploads it.

Practice

1. What is the main purpose of using docker.build() in a Jenkins pipeline?

easy

A. To run tests inside a Docker container

B. To deploy a Docker container to a cloud service

C. To remove unused Docker images from the system

D. To create a Docker image from a Dockerfile during the pipeline execution

Solution

1. Step 1: Understand the role of docker.build()

   This command is used to build Docker images from a Dockerfile within a Jenkins pipeline.

2. Step 2: Differentiate from other Docker commands

   It does not deploy containers, remove images, or run tests directly; it only builds images.

3. Final Answer:

   To create a Docker image from a Dockerfile during the pipeline execution -> Option D

4. Quick Check:

   docker.build() builds images [OK]

Hint: Remember: docker.build() creates images, not containers [OK]

Common Mistakes:

• Confusing image build with container deployment
• Thinking docker.build() removes images
• Assuming docker.build() runs tests

2. Which of the following is the correct syntax to build a Docker image named myapp inside a Jenkins pipeline script block?

easy

A. docker.build image: 'myapp'

B. docker.build('image=myapp')

C. docker.build('myapp')

D. docker.build('build myapp')

Solution

1. Step 1: Recall the correct method signature

   The docker.build() method takes the image name as a string argument, e.g., docker.build('myapp').

2. Step 2: Identify incorrect syntax

   Options A, C, and D use invalid syntax or incorrect parameter formats.

3. Final Answer:

   docker.build('myapp') -> Option C

4. Quick Check:

   Correct syntax is docker.build('imageName') [OK]

Hint: Use docker.build('imageName') inside script block [OK]

Common Mistakes:

• Using key-value syntax incorrectly
• Adding extra words inside the string
• Missing quotes around image name

3. Given this Jenkins pipeline snippet inside a script block:

def image = docker.build('myapp:latest')
image.push()

What will happen when this pipeline runs?

medium

A. Builds the Docker image 'myapp:latest' and pushes it to the default Docker registry

B. Builds the Docker image but does not push it anywhere

C. Pushes an existing image 'myapp:latest' without building it

D. Fails because image.push() is not a valid method

Solution

1. Step 1: Understand docker.build() and image.push()

   The docker.build() command builds the image and returns an object representing it. Calling image.push() pushes the built image to the Docker registry.

2. Step 2: Confirm the sequence of actions

   The code builds 'myapp:latest' and then pushes it to the default Docker registry configured in Jenkins.

3. Final Answer:

   Builds the Docker image 'myapp:latest' and pushes it to the default Docker registry -> Option A

4. Quick Check:

   docker.build() + image.push() builds and pushes [OK]

Hint: docker.build() returns image object; call push() to upload [OK]

Common Mistakes:

• Assuming push happens automatically without calling push()
• Thinking push() is invalid method
• Confusing build and push steps

4. You wrote this Jenkins pipeline snippet:

pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        docker.build('myapp')
      }
    }
  }
}

But the build fails with error: docker.build is not recognized. What is the most likely cause?

medium

A. The docker variable is not available outside a script block

B. The Dockerfile is missing in the workspace

C. The Jenkins agent does not have Docker installed

D. The image name 'myapp' is invalid

Solution

1. Step 1: Check usage of docker.build()

   In declarative pipelines, docker.build() must be called inside a script block to access the Docker DSL.

2. Step 2: Identify the error cause

   Calling docker.build() directly in steps without script causes the method to be unrecognized.

3. Final Answer:

   The docker variable is not available outside a script block -> Option A

4. Quick Check:

   Use script block for docker.build() [OK]

Hint: Always wrap docker.build() inside script block [OK]

Common Mistakes:

• Ignoring need for script block
• Assuming missing Dockerfile causes this error
• Blaming Docker installation without checking syntax

5. You want to build a Docker image in Jenkins pipeline and tag it with the current Git commit hash. Which snippet correctly achieves this inside a script block?

hard

A. def commit = sh('git rev-parse --short HEAD')
def image = docker.build('myapp:commit')

B. def commit = sh(script: 'git rev-parse --short HEAD', returnStdout: true).trim()
def image = docker.build("myapp:${commit}")

C. def commit = git rev-parse --short HEAD
def image = docker.build('myapp:${commit}')

D. def commit = sh(script: 'git rev-parse --short HEAD')
def image = docker.build('myapp:commit')

Solution

1. Step 1: Correctly capture Git commit hash in Jenkins

   Use sh with returnStdout: true and trim() to get the commit hash as a string.

2. Step 2: Use the commit variable in docker.build()

   Use double quotes and string interpolation to tag the image with the commit hash.

3. Final Answer:

   def commit = sh(script: 'git rev-parse --short HEAD', returnStdout: true).trim() def image = docker.build("myapp:${commit}") -> Option B

4. Quick Check:

   Use sh with returnStdout and string interpolation [OK]

Hint: Use sh(..., returnStdout:true).trim() and "myapp:${commit}" [OK]

Common Mistakes:

• Not using returnStdout to capture command output
• Using single quotes preventing variable interpolation
• Assigning shell command output incorrectly