Polling SCM vs Webhooks in Jenkins

Introduction

In Jenkins, Continuous Integration (CI) involves integrating code changes from multiple contributors into a shared repository frequently. Two common methods of triggering builds based on changes in source control are Polling SCM and Webhooks.

Polling SCM

Polling SCM is a method where Jenkins periodically checks the source code repository for changes. If a change is detected, Jenkins triggers a build.

Configuration Example

pipeline {
    agent any
    triggers {
        pollSCM('H/5 * * * *') // Poll every 5 minutes
    }
    stages {
        stage('Build') {
            steps {
                echo 'Building..'
            }
        }
    }
}

Webhooks

Webhooks are a way for an SCM to notify Jenkins immediately when changes are made. Instead of Jenkins polling for changes, the SCM sends a POST request to Jenkins when a change occurs.

Configuration Example

pipeline {
    agent any
    triggers {
        gitHubPush() // Triggers on GitHub webhook
    }
    stages {
        stage('Build') {
            steps {
                echo 'Building..'
            }
        }
    }
}

Comparison

Feature	Polling SCM	Webhooks
Trigger Method	Periodic checking	Immediate notification
Resource Usage	Higher (due to regular checks)	Lower (only on changes)
Latency	Depends on polling interval	Real-time
Configuration Complexity	Simple	Requires webhook setup

Best Practices

• Use webhooks when possible for immediate build triggers.
• Limit polling frequency to reduce resource usage if you must poll.
• Monitor build triggers to ensure they are functioning correctly.
• Use adequate security measures (e.g., secret tokens) for webhook endpoints.

FAQ