Labels for agent selection in Jenkins - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run the Jenkins pipeline on an agent with the label 'linux'.

Jenkins

pipeline {
  agent { label '[1]' }
  stages {
    stage('Build') {
      steps {
        echo 'Building on Linux agent'
      }
    }
  }
}

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

Alinux

Bmac

Cwindows

Ddocker

Attempts:

3 left

💡 Hint

Common Mistakes

Using a label that does not exist on any agent.

Misspelling the label name.

The label 'linux' selects agents tagged with 'linux' to run the pipeline.

2fill in blank

medium

Complete the code to run the Jenkins pipeline on an agent with the label 'docker'.

Jenkins

pipeline {
  agent { label '[1]' }
  stages {
    stage('Test') {
      steps {
        echo 'Running tests on Docker agent'
      }
    }
  }
}

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

Alinux

Bdocker

Cwindows

Dkubernetes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Docker' with uppercase D instead of 'docker'.

Selecting a label that does not exist.

The label 'docker' selects agents that have Docker installed or are tagged accordingly.

3fill in blank

hard

Fix the error in the Jenkins pipeline to correctly select an agent with the label 'windows'.

Jenkins

pipeline {
  agent { label '[1]' }
  stages {
    stage('Deploy') {
      steps {
        echo 'Deploying on Windows agent'
      }
    }
  }
}

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

Awin

BWindows

Cwin10

Dwindows

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Windows' which does not match the label.

Using shorthand labels like 'win' that are not defined.

Labels are case-sensitive; 'windows' in lowercase matches the agent label correctly.

4fill in blank

hard

Fill both blanks to run the pipeline on an agent with label 'linux' and specify the stage name as 'Build'.

Jenkins

pipeline {
  agent { label '[1]' }
  stages {
    stage('[2]') {
      steps {
        echo 'Building project'
      }
    }
  }
}

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

Alinux

BTest

CBuild

Dwindows

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up stage names with labels.

Using incorrect labels like 'windows' for a Linux agent.

The agent label is 'linux' and the stage name is 'Build' as required.

5fill in blank

hard

Fill all three blanks to run the pipeline on an agent with label 'docker', name the stage 'Test', and print 'Running tests'.

Jenkins

pipeline {
  agent { label '[1]' }
  stages {
    stage('[2]') {
      steps {
        echo '[3]'
      }
    }
  }
}

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

Alinux

BTest

CRunning tests

Ddocker

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong labels like 'linux' instead of 'docker'.

Incorrect stage names or echo messages.

The agent label is 'docker', the stage is named 'Test', and the echo prints 'Running tests'.

Practice

1.

What is the main purpose of using labels in Jenkins agent selection?

easy

A. To store job build logs

B. To change the Jenkins user interface theme

C. To tell Jenkins which agent can run a specific job

D. To configure Jenkins system settings

Solution

1. Step 1: Understand Jenkins agent labels

   Labels are tags assigned to agents to identify their capabilities or roles.

2. Step 2: Purpose of labels in job assignment

   Jenkins uses these labels to select the right agent that matches the job requirements.

3. Final Answer:

   To tell Jenkins which agent can run a specific job -> Option C

4. Quick Check:

   Labels guide agent selection = A [OK]

Hint: Labels connect jobs to suitable agents quickly [OK]

Common Mistakes:

• Thinking labels change UI or store logs
• Confusing labels with system settings

2.

Which of the following is the correct syntax to select an agent with label linux and docker in Jenkins pipeline?

easy

A. agent { label linux docker }

B. agent { label 'linux, docker' }

C. agent { label 'linux || docker' }

D. agent { label 'linux && docker' }

Solution

1. Step 1: Understand label expressions in Jenkins

   Jenkins uses logical operators like && for AND and || for OR in label expressions.

2. Step 2: Correct syntax for AND condition

   To require both labels, use 'linux && docker' inside the label field.

3. Final Answer:

   agent { label 'linux && docker' } -> Option D

4. Quick Check:

   AND labels use && = D [OK]

Hint: Use && for AND, || for OR in label expressions [OK]

Common Mistakes:

• Using space-separated labels without operators
• Using commas instead of logical operators
• Confusing AND (&&) with OR (||)

3.

Given this Jenkins pipeline snippet, what agent will run the job if agents have labels linux, docker, and gpu?

agent { label 'linux && (docker || gpu)' }

medium

A. An agent with linux and either docker or gpu labels

B. An agent with linux and gpu labels

C. An agent with both linux and docker labels

D. Any agent with linux, docker, and gpu labels all together

Solution

1. Step 1: Analyze label expression

   The expression requires the agent to have the 'linux' label AND either 'docker' OR 'gpu' label.

2. Step 2: Determine matching agents

   Agents with 'linux' plus 'docker' or 'linux' plus 'gpu' satisfy the condition.

3. Final Answer:

   An agent with linux and either docker or gpu labels -> Option A

4. Quick Check:

   linux AND (docker OR gpu) = A [OK]

Hint: Parentheses group OR conditions, AND applies outside [OK]

Common Mistakes:

• Thinking all three labels are required
• Ignoring parentheses in label expressions
• Assuming OR means both labels must be present

4.

What is wrong with this Jenkins pipeline agent label expression that causes the job to wait indefinitely?

agent { label 'linux && docker || gpu' }

medium

A. Labels must be quoted with double quotes, not single quotes

B. Missing parentheses causing wrong operator precedence

C. Using commas instead of logical operators

D. Agent label cannot contain logical operators

Solution

1. Step 1: Understand operator precedence in label expressions

   Logical AND (&&) has higher precedence than OR (||), so expression is parsed as '(linux && docker) || gpu'.

2. Step 2: Identify why job waits

   If no agent has both linux and docker, but some have gpu alone, job may pick gpu agents. If gpu agents are missing or busy, job waits.

3. Final Answer:

   Missing parentheses causing wrong operator precedence -> Option B

4. Quick Check:

   Use parentheses to control label logic = C [OK]

Hint: Use parentheses to clarify label logic precedence [OK]

Common Mistakes:

• Ignoring operator precedence in label expressions
• Using wrong quote types
• Believing logical operators are not allowed

5.

You want a Jenkins job to run only on agents that have linux and docker labels but never on agents with gpu label. Which label expression should you use?

hard

A. linux && docker && !gpu

B. linux && docker || !gpu

C. linux && (docker || !gpu)

D. linux && docker && gpu

Solution

1. Step 1: Understand label requirements

   The job must run on agents with both 'linux' and 'docker' labels, but exclude any with 'gpu'.

2. Step 2: Construct correct label expression

   Use AND (&&) for required labels and NOT (!) to exclude 'gpu': 'linux && docker && !gpu'.

3. Final Answer:

   linux && docker && !gpu -> Option A

4. Quick Check:

   Include linux and docker, exclude gpu = B [OK]

Hint: Use ! to exclude labels in Jenkins expressions [OK]

Common Mistakes:

• Using OR instead of AND for required labels
• Not excluding gpu label properly
• Misplacing parentheses causing wrong logic