Custom notification logic in Jenkins - Commands & Configuration

Introduction

Sometimes you want Jenkins to send messages only when certain things happen, like a build failing or succeeding. Custom notification logic lets you control exactly when and how Jenkins sends these messages to your team.

When you want to send a Slack message only if the build fails.

When you want to email the team only if tests fail but skip notifications on success.

When you want to notify different people depending on the branch being built.

When you want to send a summary notification after multiple jobs finish.

When you want to avoid spamming notifications for repeated failures.

Config File - Jenkinsfile

Jenkinsfile

pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        echo 'Building...'
        // Simulate build step
      }
    }
    stage('Test') {
      steps {
        echo 'Testing...'
        // Simulate test step
      }
    }
  }
  post {
    success {
      script {
        if (env.BRANCH_NAME == 'main') {
          slackSend(channel: '#builds', message: "Build succeeded on main branch: ${env.JOB_NAME} #${env.BUILD_NUMBER}")
        }
      }
    }
    failure {
      slackSend(channel: '#alerts', message: "Build failed: ${env.JOB_NAME} #${env.BUILD_NUMBER}")
    }
  }
}

This Jenkinsfile defines a pipeline with build and test stages.

The post section controls notifications:

• success: Sends a Slack message only if the build succeeds on the main branch.
• failure: Sends a Slack message to alert channel if the build fails.

This way, notifications are customized based on build result and branch.

Commands

This command updates the Jenkins job configuration with the new Jenkinsfile containing custom notification logic.

Terminal

jenkins-jobs --conf jenkins.ini update Jenkinsfile

Expected Output

Job updated successfully

Starts a build of the Jenkins pipeline to test the notification logic in action.

Terminal

jenkins build my-pipeline

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] echo

Building...

[Pipeline] echo

Testing...

[Pipeline] slackSend

Sending Slack message to #builds

[Pipeline] End of Pipeline

Finished: SUCCESS

Simulates a build failure to verify that failure notifications are sent correctly.

Terminal

jenkins build my-pipeline --simulate-failure

Expected Output

[Pipeline] Start of Pipeline

[Pipeline] echo

Building...

[Pipeline] echo

Testing...

[Pipeline] slackSend

Sending Slack message to #alerts

[Pipeline] End of Pipeline

Finished: FAILURE

Key Concept

If you remember nothing else from this pattern, remember: use the post section in Jenkinsfile to run notification steps conditionally based on build results and environment variables.

Common Mistakes

Placing notification steps inside the main stages instead of the post section.

Notifications may run even if the build fails early or skip important conditions.

Use the post section with success, failure, or always blocks to control notifications reliably.

Hardcoding notification channels without checking branch or build context.

Leads to irrelevant notifications and spamming the wrong teams.

Use environment variables like BRANCH_NAME to customize notification targets.

Not testing notification logic with both success and failure builds.

You might miss bugs where notifications never send or send incorrectly.

Run builds simulating success and failure to verify all notification paths.

Summary

Use the post section in Jenkinsfile to add custom notification logic after build stages.

Send notifications conditionally based on build status like success or failure.

Use environment variables to customize who gets notified and when.

Practice

1. What is the main purpose of using custom notification logic in Jenkins pipelines?

easy

A. To send notifications for every build regardless of status

B. To restart the Jenkins server automatically after each build

C. To disable all notifications permanently

D. To send notifications only when specific build conditions are met

Solution

1. Step 1: Understand notification goals

   Custom notification logic aims to reduce noise by sending alerts only when necessary.

2. Step 2: Identify correct behavior

   Sending notifications only on specific build results (like failure) keeps the team focused.

3. Final Answer:

   To send notifications only when specific build conditions are met -> Option D

4. Quick Check:

   Custom notifications = selective alerts [OK]

Hint: Think about reducing alert noise to stay focused [OK]

Common Mistakes:

• Assuming notifications should always be sent
• Confusing disabling notifications with custom logic
• Believing Jenkins restarts after every build

2. Which Jenkins pipeline syntax correctly checks if the build failed before sending a notification?

easy

A. if (currentBuild.result = 'FAILURE') { notify() }

B. if (build.status == 'SUCCESS') { notify() }

C. if (currentBuild.currentResult == 'FAILURE') { notify() }

D. if (currentBuild.currentResult === FAILURE) { notify() }

Solution

1. Step 1: Identify correct property and comparison

   Use currentBuild.currentResult to get build status and compare with string 'FAILURE'.

2. Step 2: Check syntax correctness

   if (currentBuild.currentResult == 'FAILURE') { notify() } uses correct equality operator (==) and string comparison.

3. Final Answer:

   if (currentBuild.currentResult == 'FAILURE') { notify() } -> Option C

4. Quick Check:

   Correct property and comparison = if (currentBuild.currentResult == 'FAILURE') { notify() } [OK]

Hint: Use currentBuild.currentResult with 'FAILURE' string and == [OK]

Common Mistakes:

• Using single equals (=) instead of double (==)
• Comparing to SUCCESS instead of FAILURE
• Missing quotes around 'FAILURE'
• Using undefined variable FAILURE without quotes

3. Given this Jenkins pipeline snippet:

post {
  failure {
    script {
      if (currentBuild.previousBuild?.result == 'SUCCESS') {
        notify('Build failed after success')
      }
    }
  }
}

What happens if the previous build was successful and the current build failed?

medium

A. Notification 'Build failed after success' is sent

B. No notification is sent

C. Notification is sent only if current build succeeded

D. Pipeline throws a syntax error

Solution

1. Step 1: Analyze condition in failure block

   The post.failure block runs only if current build failed. Inside, it checks if previous build result was 'SUCCESS'.

2. Step 2: Evaluate condition outcome

   If previous build was successful and current failed, condition is true, so notify is called with the message.

3. Final Answer:

   Notification 'Build failed after success' is sent -> Option A

4. Quick Check:

   Previous success + current failure triggers notification [OK]

Hint: Check previousBuild?.result and current failure block [OK]

Common Mistakes:

• Thinking notification sends on success builds
• Ignoring the safe navigation operator '?'
• Assuming syntax error due to optional chaining

4. You wrote this Jenkins pipeline snippet to notify only on failure after success:

post {
  failure {
    script {
      if (currentBuild.previousBuild.result == 'SUCCESS') {
        notify('Failed after success')
      }
    }
  }
}

But it sometimes throws a NullPointerException. What is the likely cause?

medium

A. notify function is undefined

B. previousBuild can be null, so accessing result causes error

C. failure block cannot contain if statements

D. currentBuild.previousBuild.result is always 'FAILURE'

Solution

1. Step 1: Identify potential null values

   currentBuild.previousBuild can be null if no previous build exists.

2. Step 2: Understand error cause

   Accessing result on null causes NullPointerException. Safe navigation operator ?. avoids this.

3. Final Answer:

   previousBuild can be null, so accessing result causes error -> Option B

4. Quick Check:

   Null previousBuild causes error without safe navigation [OK]

Hint: Use ?. to safely access previousBuild properties [OK]

Common Mistakes:

• Ignoring possibility of null previousBuild
• Assuming notify is always defined
• Thinking failure block disallows if statements

5. You want to send a notification only when the build status changes from SUCCESS to FAILURE or from FAILURE to SUCCESS. Which Jenkins pipeline snippet correctly implements this logic?

hard

A. post {
failure {
script {
if (currentBuild.previousBuild?.result == 'SUCCESS') {
notify('Failed after success')
}
}
}
success {
script {
if (currentBuild.previousBuild?.result == 'FAILURE') {
notify('Succeeded after failure')
}
}
}
}

B. post {
success {
notify('Build succeeded')
}
failure {
notify('Build failed')
}
}

C. post {
always {
script {
if (currentBuild.previousBuild?.result != currentBuild.currentResult) {
notify('Build status changed')
}
}
}
}

D. post {
always {
notify('Build finished')
}
}

Solution

1. Step 1: Understand the requirement

   Notify only when build status flips between SUCCESS and FAILURE, not on every build.

2. Step 2: Analyze each option

   post { failure { script { if (currentBuild.previousBuild?.result == 'SUCCESS') { notify('Failed after success') } } } success { script { if (currentBuild.previousBuild?.result == 'FAILURE') { notify('Succeeded after failure') } } } } checks previous build result and current build result in success and failure blocks separately, sending notifications only on status change.

3. Final Answer:

   post { failure { script { if (currentBuild.previousBuild?.result == 'SUCCESS') { notify('Failed after success') } } } success { script { if (currentBuild.previousBuild?.result == 'FAILURE') { notify('Succeeded after failure') } } } } -> Option A

4. Quick Check:

   Status change detection needs previousBuild checks in success and failure blocks [OK]

Hint: Check previousBuild result differs from current in success and failure blocks [OK]

Common Mistakes:

• Sending notifications on every build regardless of status change
• Not checking previous build result
• Using always block without condition