Docker agent in Jenkinsfile - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify a Docker agent in the Jenkinsfile.

Jenkins

pipeline {
  agent {
    docker {
      image '[1]'
    }
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building inside Docker container'
      }
    }
  }
}

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

Aalpine:3.12

Bnode:14

Cpython:3.8

Dubuntu:latest

Attempts:

3 left

💡 Hint

Common Mistakes

Using an invalid image name.

Forgetting to put the image name in quotes.

The docker agent requires an image name. Here, node:14 is used as the Docker image.

2fill in blank

medium

Complete the code to add a custom Docker argument in the Jenkinsfile.

Jenkins

pipeline {
  agent {
    docker {
      image 'python:3.8'
      args '[1]'
    }
  }
  stages {
    stage('Test') {
      steps {
        echo 'Running tests inside Docker'
      }
    }
  }
}

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

A--rm

B--privileged

C-d

D-v /tmp:/tmp

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid Docker arguments.

Not quoting the args string.

The args field lets you pass extra Docker run options. Here, -v /tmp:/tmp mounts a volume.

3fill in blank

hard

Fix the error in the Jenkinsfile Docker agent declaration.

Jenkins

pipeline {
  agent {
    docker {
      image '[1]'
    }
  }
  stages {
    stage('Deploy') {
      steps {
        echo 'Deploying inside Docker container'
      }
    }
  }
}

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

Anode:14

Bnode-14

Cnode14

Dnode/14

Attempts:

3 left

💡 Hint

Common Mistakes

Using colon after image key.

Using invalid image names.

The syntax for the Docker agent does not use a colon after image. The correct image name is node:14.

4fill in blank

hard

Fill both blanks to specify a Docker agent with a custom image and reuse the workspace.

Jenkins

pipeline {
  agent {
    docker {
      image '[1]'
      reuseNode [2]
    }
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building with Docker agent'
      }
    }
  }
}

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

Amaven:3.6.3-jdk-11

Btrue

Cfalse

Dnode:16

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid image names.

Setting reuseNode to a string instead of boolean.

The image is set to maven:3.6.3-jdk-11 and reuseNode is set to true to reuse the workspace.

5fill in blank

hard

Fill all three blanks to define a Docker agent with image, args, and label.

Jenkins

pipeline {
  agent {
    docker {
      image '[1]'
      args '[2]'
      label '[3]'
    }
  }
  stages {
    stage('Test') {
      steps {
        echo 'Testing inside Docker container'
      }
    }
  }
}

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

Apython:3.9-slim

B-v /var/run/docker.sock:/var/run/docker.sock

Cdocker-agent

Dnode:12-alpine

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid Docker arguments.

Forgetting to quote the label string.

The Docker agent uses the python:3.9-slim image, mounts the Docker socket with -v /var/run/docker.sock:/var/run/docker.sock, and uses the label docker-agent.

Practice

1. What is the main purpose of using a docker agent in a Jenkinsfile?

easy

A. To speed up the Jenkins UI loading time

B. To run the build inside a container for a consistent environment

C. To deploy the application automatically after build

D. To backup Jenkins configuration files

Solution

1. Step 1: Understand what a Docker agent does in Jenkins

   A Docker agent runs the build steps inside a Docker container, ensuring the environment is consistent and isolated.

2. Step 2: Compare options with this purpose

   Only To run the build inside a container for a consistent environment describes running builds inside containers for consistency. Other options describe unrelated tasks.

3. Final Answer:

   To run the build inside a container for a consistent environment -> Option B

4. Quick Check:

   Docker agent purpose = consistent build environment [OK]

Hint: Docker agent means build runs inside container [OK]

Common Mistakes:

• Confusing Docker agent with deployment step
• Thinking Docker agent speeds up UI
• Assuming Docker agent manages backups

2. Which of the following is the correct syntax to specify a Docker agent in a Jenkinsfile?

easy

A. agent { docker image 'node:14' }

B. agent docker image: 'node:14'

C. agent docker { 'node:14' }

D. agent { docker { image 'node:14' } }

Solution

1. Step 1: Recall Jenkinsfile Docker agent syntax

   The correct syntax uses a block: agent { docker { image 'node:14' } }.

2. Step 2: Check each option

   agent { docker { image 'node:14' } } matches the correct block syntax. Options A, B, and D have syntax errors or missing braces.

3. Final Answer:

   agent { docker { image 'node:14' } } -> Option D

4. Quick Check:

   Correct Docker agent syntax = agent { docker { image 'node:14' } } [OK]

Hint: Docker agent uses nested braces with image key [OK]

Common Mistakes:

• Omitting braces around docker block
• Using colon instead of braces
• Placing image outside docker block

3. Given this Jenkinsfile snippet:

pipeline {
  agent {
    docker {
      image 'python:3.12'
      args '-v /tmp:/tmp'
    }
  }
  stages {
    stage('Test') {
      steps {
        sh 'python --version'
      }
    }
  }
}

What will be the output of the sh 'python --version' command?

medium

A. Python 3.12.x

B. Python 2.7.x

C. Command not found error

D. Python 3.8.x

Solution

1. Step 1: Identify the Docker image used

   The image specified is 'python:3.12', which contains Python version 3.12.

2. Step 2: Understand the command inside the container

   The command python --version runs inside the container, so it will output the Python version installed in that image, which is 3.12.x.

3. Final Answer:

   Python 3.12.x -> Option A

4. Quick Check:

   Docker image version matches command output [OK]

Hint: Output matches Docker image Python version [OK]

Common Mistakes:

• Assuming host Python version is used
• Confusing image tag with Python version
• Expecting command not found error

4. You wrote this Jenkinsfile snippet:

pipeline {
  agent {
    docker {
      image 'ubuntu'
      args '-it'
    }
  }
  stages {
    stage('Build') {
      steps {
        sh 'echo Hello'
      }
    }
  }
}

But the build fails with error: docker: Error response from daemon: the input device is not a TTY. What is the best fix?

medium

A. Change image to ubuntu:latest

B. Add tty true to the docker agent block

C. Remove the -it argument from args

D. Replace sh with bat

Solution

1. Step 1: Understand the error message

   The error says the input device is not a TTY, caused by using -it (interactive + tty) in a non-interactive Jenkins build.

2. Step 2: Fix the Docker args

   Removing -it from args avoids requesting a TTY, fixing the error.

3. Final Answer:

   Remove the -it argument from args -> Option C

4. Quick Check:

   Remove interactive TTY args in Jenkins Docker agent [OK]

Hint: Avoid -it args in Jenkins Docker agents [OK]

Common Mistakes:

• Adding tty true without removing -it
• Changing image without fixing args
• Using Windows bat step on Linux agent

5. You want to run a Jenkins pipeline using a Docker agent with the image maven:3.8.6-jdk-17 and mount the host directory /var/maven-repo to /root/.m2/repository inside the container. Which Jenkinsfile snippet correctly sets this up?

hard

A. agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo:/root/.m2/repository' } }

B. agent { docker { image 'maven:3.8.6-jdk-17' args '-v /root/.m2/repository:/var/maven-repo' } }

C. agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo' } }

D. agent { docker { image 'maven:3.8.6-jdk-17' args '--mount source=/var/maven-repo,target=/root/.m2/repository' } }

Solution

1. Step 1: Understand Docker volume mount syntax

   The syntax to mount a host directory to a container path is -v host_path:container_path.

2. Step 2: Match the mount paths correctly

   The host directory /var/maven-repo should be mounted to /root/.m2/repository inside the container, so the args must be -v /var/maven-repo:/root/.m2/repository.

3. Step 3: Check options

   agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo:/root/.m2/repository' } } matches the correct syntax and paths. agent { docker { image 'maven:3.8.6-jdk-17' args '-v /root/.m2/repository:/var/maven-repo' } } reverses paths. agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo' } } misses container path. agent { docker { image 'maven:3.8.6-jdk-17' args '--mount source=/var/maven-repo,target=/root/.m2/repository' } } uses incorrect mount syntax for Docker CLI.

4. Final Answer:

   agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo:/root/.m2/repository' } } -> Option A

5. Quick Check:

   Correct volume mount syntax = agent { docker { image 'maven:3.8.6-jdk-17' args '-v /var/maven-repo:/root/.m2/repository' } } [OK]

Hint: Use -v host:container for volume mounts in Docker args [OK]

Common Mistakes:

• Reversing host and container paths
• Omitting container path in volume mount
• Using --mount instead of -v in args