Stage conditions with when directive in Jenkins - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the when directive in a Jenkins pipeline stage?

The when directive controls whether a stage runs or is skipped based on specified conditions, helping to make pipelines more flexible and efficient.

beginner

Name two common conditions you can use inside the when directive.

You can use conditions like branch to run a stage only on specific branches, and environment to run a stage only if an environment variable matches a value.

intermediate

How does the when directive improve pipeline efficiency?

By skipping stages that are not needed based on conditions, it saves time and resources, similar to deciding not to cook a meal if you already have leftovers.

beginner

What happens if the when condition in a stage evaluates to false?

The stage is skipped and does not run, but the pipeline continues with the next stages.

beginner

Write a simple example of a Jenkins stage that runs only on the 'main' branch using the when directive.

stage('Deploy') { when { branch 'main' } steps { echo 'Deploying to production' } }

What does the when directive do in a Jenkins pipeline stage?

A Controls if the stage runs based on conditions

B Defines the steps inside a stage

C Sets environment variables

D Triggers another pipeline

The when directive controls whether a stage runs or is skipped based on conditions.

Which condition would you use to run a stage only on a specific branch?

A environment

B changeset

C expression

D branch

The branch condition runs the stage only on specified branches.

If a when condition is false, what happens to the stage?

A Pipeline stops

B It runs anyway

C It skips the stage

D Pipeline restarts

The stage is skipped but the pipeline continues.

Which of these is NOT a valid when condition in Jenkins?

A branch

B time

C environment

D expression

There is no built-in time condition in Jenkins when directive.

How can you combine multiple conditions in a when directive?

A Using <code>allOf</code> or <code>anyOf</code>

B Using <code>and</code> or <code>or</code> keywords

C Using <code>if</code> statements

D You cannot combine conditions

Jenkins supports combining conditions with allOf (AND) and anyOf (OR).

Explain how the when directive helps control the flow of a Jenkins pipeline.

Think about how you decide to do or skip tasks based on conditions in daily life.

Describe how you would use multiple conditions inside a when directive to run a stage only on the 'main' branch and when an environment variable is set to 'production'.

Combine conditions using <code>allOf</code> to require both to be true.

Practice

1. What is the main purpose of the when directive in a Jenkins pipeline stage?

easy

A. To set the timeout for a stage execution

B. To define environment variables for a stage

C. To specify the agent where the stage runs

D. To control whether a stage runs based on specified conditions

Solution

1. Step 1: Understand the role of when directive

   The when directive is used to decide if a stage should run or be skipped based on conditions.

2. Step 2: Compare with other stage directives

   Other directives like environment, agent, and timeout serve different purposes unrelated to conditional execution.

3. Final Answer:

   To control whether a stage runs based on specified conditions -> Option D

4. Quick Check:

   when controls stage execution [OK]

Hint: Remember: when decides if stage runs or skips [OK]

Common Mistakes:

• Confusing when with environment
• Thinking when sets agent or timeout
• Assuming when always runs the stage

2. Which of the following is the correct syntax to run a stage only on the 'main' branch using the when directive?

easy

A. when {
branch 'main'
}

B. when {
branch == 'main'
}

C. when {
if (branch == 'main')
}

D. when {
branch: 'main'
}

Solution

1. Step 1: Recall correct when syntax for branch condition

   The correct syntax uses branch 'branchName' inside when block without operators or colons.

2. Step 2: Identify syntax errors in other options

   Options B and C use invalid operators or expressions; D uses colon which is incorrect in this context.

3. Final Answer:

   when { branch 'main' } -> Option A

4. Quick Check:

   Use branch 'name' syntax [OK]

Hint: Use branch 'name' without operators in when [OK]

Common Mistakes:

• Using comparison operators inside when
• Adding colons or equal signs incorrectly
• Writing if statements inside when

3. Given the following Jenkins pipeline snippet, what will happen if the branch is 'feature'?

stage('Deploy') {
  when {
    branch 'main'
  }
  steps {
    echo 'Deploying to production'
  }
}

medium

A. The stage will run and print 'Deploying to production'

B. The stage will be skipped and nothing will print

C. The pipeline will fail with a syntax error

D. The stage will run but print nothing

Solution

1. Step 1: Understand the when condition

   The stage runs only if the branch is 'main'. Since the branch is 'feature', the condition is false.

2. Step 2: Determine stage behavior on false condition

   When when condition is false, Jenkins skips the stage and does not execute steps.

3. Final Answer:

   The stage will be skipped and nothing will print -> Option B

4. Quick Check:

   Branch mismatch skips stage [OK]

Hint: If branch doesn't match, stage is skipped silently [OK]

Common Mistakes:

• Assuming stage runs regardless of branch
• Expecting syntax error for valid when
• Thinking stage runs but steps don't print

4. Identify the error in this Jenkins pipeline stage that uses when:

stage('Test') {
  when {
    branch == 'dev'
  }
  steps {
    echo 'Running tests'
  }
}

medium

A. The stage name 'Test' is not allowed

B. Missing agent directive for the stage

C. Using '==' operator inside when is invalid syntax

D. The steps block should be inside when

Solution

1. Step 1: Check when syntax for branch condition

   The when directive expects branch 'name' without operators like '=='.

2. Step 2: Validate other parts of the stage

   Missing agent is allowed if inherited; steps must be outside when; stage name is valid.

3. Final Answer:

   Using '==' operator inside when is invalid syntax -> Option C

4. Quick Check:

   No operators in when branch condition [OK]

Hint: No operators like '==' inside when branch check [OK]

Common Mistakes:

• Using comparison operators inside when
• Placing steps inside when
• Assuming stage name restrictions

5. You want a Jenkins stage to run only when the branch is 'release' and an environment variable DEPLOY is set to 'true'. Which when directive correctly implements this?

hard

A. when {
allOf {
branch 'release'
environment name: 'DEPLOY', value: 'true'
}
}

B. when {
branch 'release' && environment name: 'DEPLOY', value: 'true'
}

C. when {
branch 'release'
environment 'DEPLOY': 'true'
}

D. when {
anyOf {
branch 'release'
environment name: 'DEPLOY', value: 'true'
}
}

Solution

1. Step 1: Understand combining conditions in when

   To require both conditions, use allOf block combining branch and environment.

2. Step 2: Analyze each option's logic

   when {
     allOf {
       branch 'release'
       environment name: 'DEPLOY', value: 'true'
     }
   }

   correctly uses allOf.

   when {
     branch 'release' && environment name: 'DEPLOY', value: 'true'
   }

   uses invalid syntax with '&&'.

   when {
     branch 'release'
     environment 'DEPLOY': 'true'
   }

   uses invalid syntax for environment condition (missing name: and value:).

   when {
     anyOf {
       branch 'release'
       environment name: 'DEPLOY', value: 'true'
     }
   }

   uses anyOf, meaning either condition suffices.

3. Final Answer:

   when { allOf { branch 'release' environment name: 'DEPLOY', value: 'true' } } -> Option A

4. Quick Check:

   Use allOf to combine multiple when conditions [OK]

Hint: Use allOf to require all conditions true [OK]

Common Mistakes:

• Using '&&' inside when block
• Using environment 'VAR': 'value' shorthand syntax
• Using anyOf when all conditions are needed