How to Use Triggers in Jenkins Pipeline for Automated Builds

In Jenkins Pipeline, you use the triggers block inside your pipeline to define events that start your build automatically, such as SCM changes or scheduled cron jobs. Common triggers include pollSCM for source code changes and cron for timed builds.

Syntax

The triggers block defines when the pipeline should start automatically. It is placed inside the pipeline block or set as job properties. Common triggers include:

• pollSCM('cron-syntax'): Checks source code changes at intervals.
• cron('cron-syntax'): Runs the pipeline on a schedule.
• upstream(triggeredJob): Starts when another job finishes.

Example syntax inside a declarative pipeline:

groovy

pipeline {
  triggers {
    pollSCM('H/15 * * * *')
    cron('H 4 * * 1-5')
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building...'
      }
    }
  }
}

Example

This example shows a Jenkins declarative pipeline that triggers a build every 15 minutes if there are SCM changes and also runs at 4 AM on weekdays regardless of changes.

groovy

pipeline {
  agent any
  triggers {
    pollSCM('H/15 * * * *')
    cron('H 4 * * 1-5')
  }
  stages {
    stage('Build') {
      steps {
        echo 'Starting build triggered by SCM change or schedule.'
      }
    }
  }
}

Output

[Pipeline] Start of Pipeline
[Pipeline] echo
Starting build triggered by SCM change or schedule.
[Pipeline] End of Pipeline

Common Pitfalls

Common mistakes when using triggers in Jenkins pipelines include:

• Using pollSCM without SCM configured, so no builds trigger.
• Incorrect cron syntax causing triggers to never run.
• Placing triggers outside the pipeline block in declarative pipelines.
• Expecting pollSCM to trigger immediately after a commit; it only checks on schedule.

Example of wrong and right placement:

groovy

// Wrong: triggers outside pipeline block
triggers {
  pollSCM('H/15 * * * *')
}
pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        echo 'Build'
      }
    }
  }
}

// Right: triggers inside pipeline block
pipeline {
  agent any
  triggers {
    pollSCM('H/15 * * * *')
  }
  stages {
    stage('Build') {
      steps {
        echo 'Build'
      }
    }
  }
}

Quick Reference

Here is a quick summary of common Jenkins pipeline triggers:

Trigger	Description	Example
pollSCM	Checks source code changes on schedule	pollSCM('H/15 * * * *')
cron	Runs pipeline on a fixed schedule	cron('H 4 * * 1-5')
upstream	Triggers when another job completes	upstream('OtherJob')
githubPush	Triggers on GitHub push events (requires plugin)	githubPush()

Key Takeaways

Use the triggers block inside the pipeline to automate build starts.

pollSCM triggers builds on source code changes at scheduled intervals.

cron triggers builds on a fixed time schedule using cron syntax.

Always place triggers inside the pipeline block in declarative pipelines.

Check cron syntax carefully to avoid missed or unexpected triggers.