Docker Pipeline plugin in Jenkins - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to build a Docker image named 'myapp' using the Docker Pipeline plugin.

Jenkins

docker.build('[1]')

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

Abuild

Bimage

Cmyapp

Dcontainer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' or 'container' instead of the image name.

Leaving the argument empty.

The docker.build() function requires the image name as a string argument. Here, 'myapp' is the correct image name.

2fill in blank

medium

Complete the code to run a Docker container from the image 'myapp' and execute the command 'echo Hello'.

Jenkins

docker.image('myapp').[1]('echo Hello')

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

Arun

Bbuild

Cinside

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' which is for building images.

Using 'inside' which is for running commands inside an existing container context.

The run() method runs a container from the specified image and executes the given command inside it.

3fill in blank

hard

Fix the error in the code to push the Docker image 'myapp' to the registry.

Jenkins

docker.image('myapp').[1]()

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

Apush

Bpublish

Cupload

Ddeploy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'publish' or 'upload' which are not valid methods.

Using 'deploy' which is unrelated to Docker image pushing.

The push() method uploads the Docker image to the configured Docker registry.

4fill in blank

hard

Fill both blanks to run a command inside a Docker container with a custom environment variable.

Jenkins

docker.image('myapp').inside("-e [1]=[2]") {
  sh 'printenv'
}

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

AMY_VAR

BVALUE

CENV_VAR

D123

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping variable name and value.

Using invalid method names or flags.

The inside() method runs commands inside a container. The -e flag sets environment variables. Here, 'MY_VAR' is the variable name and 'VALUE' is its value.

5fill in blank

hard

Fill all three blanks to build a Docker image, tag it with 'latest', and push it to the registry.

Jenkins

def app = docker.[1]('[2]')
app.[3]()

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

Abuild

Bmyapp:latest

Cpush

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' instead of 'push' to upload the image.

Omitting the tag in the image name.

First, docker.build() builds the image with the tag 'myapp:latest'. Then, push() uploads it to the registry.

Practice

1. What is the primary purpose of the docker.build() method in Jenkins Docker Pipeline plugin?

easy

A. To remove unused Docker images

B. To run a Docker container interactively

C. To build a Docker image from a Dockerfile

D. To push a Docker image to a registry

Solution

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

   This method is used to create a Docker image from a Dockerfile in the workspace.

2. Step 2: Differentiate from other Docker Pipeline methods

   Running containers uses docker.image().inside { }, pushing uses docker.withRegistry(), and removing images is not handled by docker.build().

3. Final Answer:

   To build a Docker image from a Dockerfile -> Option C

4. Quick Check:

   docker.build() builds images [OK]

Hint: Remember: build = create image from Dockerfile [OK]

Common Mistakes:

• Confusing build with push or run commands
• Thinking docker.build() runs containers
• Assuming it handles image removal

2. Which of the following is the correct syntax to run commands inside a Docker container in a Jenkins pipeline?

easy

A. docker.image('myimage').inside { sh 'echo Hello' }

B. docker.build('myimage') { sh 'echo Hello' }

C. docker.run('myimage') { sh 'echo Hello' }

D. docker.container('myimage').exec { sh 'echo Hello' }

Solution

1. Step 1: Identify the correct method to run commands inside a container

   The docker.image('myimage').inside { } syntax runs commands inside a container created from the image.

2. Step 2: Check other options for syntax errors or misuse

   docker.run() and docker.container() are not valid Jenkins Pipeline methods; docker.build() builds images but does not run containers.

3. Final Answer:

   docker.image('myimage').inside { sh 'echo Hello' } -> Option A

4. Quick Check:

   Use docker.image().inside { } to run commands [OK]

Hint: Use docker.image().inside { } to run commands inside containers [OK]

Common Mistakes:

• Using docker.build() to run commands
• Trying to use non-existent methods like docker.run()
• Confusing image build and container run syntax

3. Given the following Jenkins pipeline snippet, what will be the output of the sh command inside the container?

def img = docker.build('myapp:latest')
img.inside {
  sh 'echo Hello from Docker'
}

medium

A. Error: No such image 'myapp:latest'

B. Hello from Docker

C. Build logs of the Docker image

D. Nothing, the command is not executed

Solution

1. Step 1: Understand the build and run sequence

   The docker.build('myapp:latest') creates the image, then img.inside { } runs commands inside a container from that image.

2. Step 2: Analyze the sh command inside the container

   The shell command echo Hello from Docker runs inside the container and outputs the string.

3. Final Answer:

   Hello from Docker -> Option B

4. Quick Check:

   Commands inside img.inside { } run and output normally [OK]

Hint: Commands inside img.inside { } run inside container [OK]

Common Mistakes:

• Assuming build only creates logs, not image
• Thinking the command runs outside the container
• Expecting an error if image was just built

4. Identify the error in this Jenkins pipeline snippet using Docker Pipeline plugin:

docker.withRegistry('https://myregistry.com', 'my-credentials') {
  def img = docker.build('myapp')
  img.push()
}
img.inside {
  sh 'echo Running inside container'
}

medium

A. The img.push() should be called before docker.withRegistry

B. The docker.build method is missing the Dockerfile path

C. The credentials ID 'my-credentials' is invalid syntax

D. The img.inside block is outside the docker.withRegistry block and will fail

Solution

1. Step 1: Check scope of img variable

   The variable img is defined inside the docker.withRegistry block, so it is not accessible outside that block.

2. Step 2: Identify the error with img.inside usage

   Using img.inside outside the block where img is defined causes a runtime error because img is undefined there.

3. Final Answer:

   The img.inside block is outside the docker.withRegistry block and will fail -> Option D

4. Quick Check:

   Variable scope matters in Jenkins pipeline blocks [OK]

Hint: Keep variable usage inside the block where it's defined [OK]

Common Mistakes:

• Assuming variables are global across blocks
• Confusing credentials ID syntax
• Thinking push must be outside withRegistry

5. You want to build a Docker image, run tests inside a container from that image, and then push the image to a private registry using Jenkins Docker Pipeline plugin. Which pipeline snippet correctly implements this workflow?

hard

A. def img = docker.build('myapp:test')
img.inside {
sh 'run-tests.sh'
}
docker.withRegistry('https://registry.example.com', 'creds') {
img.push()
}

B. docker.withRegistry('https://registry.example.com', 'creds') {
def img = docker.build('myapp:test')
img.push()
img.inside {
sh 'run-tests.sh'
}
}

C. docker.withRegistry('https://registry.example.com', 'creds') {
img.push()
def img = docker.build('myapp:test')
img.inside {
sh 'run-tests.sh'
}
}

D. def img = docker.build('myapp:test')
docker.withRegistry('https://registry.example.com', 'creds') {
img.push()
}
img.inside {
sh 'run-tests.sh'
}

Solution

1. Step 1: Build image and run tests inside container first

   The image must be built before running tests inside it, so docker.build() and img.inside { } come first.

2. Step 2: Push image inside docker.withRegistry() block after tests

   Pushing requires registry credentials, so img.push() must be inside docker.withRegistry() block after tests pass.

3. Step 3: Verify variable scope and order

   def img = docker.build('myapp:test') img.inside { sh 'run-tests.sh' } docker.withRegistry('https://registry.example.com', 'creds') { img.push() } correctly builds image, runs tests inside container, then pushes image with credentials in proper order and scope.

4. Final Answer:

   def img = docker.build('myapp:test') img.inside { sh 'run-tests.sh' } docker.withRegistry('https://registry.example.com', 'creds') { img.push() } -> Option A

5. Quick Check:

   Build -> Test inside container -> Push with credentials [OK]

Hint: Build first, test inside container, then push inside withRegistry [OK]

Common Mistakes:

• Pushing image before running tests
• Using img.inside after pushing outside scope
• Defining variables inside wrong blocks