Build Triggers — Poll SCM, Webhook, Cron

Right now you click "Build Now" to run the pipeline. That is manual. The whole point of CI is automation. You need triggers — something that starts the pipeline without human intervention. There are three ways: polling, webhooks, and cron scheduling.

Three Types of Triggers

Poll SCM — Check Git Periodically

pipeline {
    agent any

    triggers {
        // Check Git for changes every 5 minutes
        pollSCM('H/5 * * * *')
    }

    stages {
        // ... your stages here
    }
}

Every 5 minutes, Jenkins asks Git: "Any new commits since my last check?" If yes, it runs the pipeline. If no, it does nothing. Simple but wasteful — Jenkins keeps asking even when nobody is pushing code.

Cron — Schedule Nightly Regression

triggers {
    // Run full regression at 2 AM on weekdays
    cron('H 2 * * 1-5')
}

Cron Syntax — 5 Fields

# MINUTE  HOUR  DAY_OF_MONTH  MONTH  DAY_OF_WEEK
# 0-59    0-23    1-31        1-12    0-7 (0 and 7 = Sunday)

# H = hash — Jenkins picks a random minute to spread load
# Without H, if 50 jobs all say "0 2 * * *", they ALL start at 2:00 AM
# With H, they spread across 2:00-2:59 AM

H 2 * * 1-5       # Weekdays at ~2 AM (nightly regression)
H/15 * * * *       # Every 15 minutes (aggressive polling)
H 8 * * *          # Daily at ~8 AM (morning smoke)
H 22 * * 5         # Every Friday at ~10 PM (weekend regression)
H 6,18 * * 1-5     # Weekdays at ~6 AM and ~6 PM (twice daily)

Webhook — Instant Trigger on Push

Webhooks are the professional approach. Instead of Jenkins polling Git every 5 minutes, GitHub tells Jenkins the moment someone pushes code. Instant. No wasted resources.

Set Up GitHub Webhook

1. In Jenkins: Go to your Pipeline job > Configure > Build Triggers > Check "GitHub hook trigger for GITScm polling."
2. In GitHub: Go to your repo > Settings > Webhooks > Add webhook.
3. Payload URL: http://your-jenkins-url:8080/github-webhook/
4. Content type: application/json.
5. Which events: Select "Just the push event."
6. Click "Add webhook." Green checkmark means it is working.

Best Practice: Combine Triggers

triggers {
    // Instant trigger on push (for smoke tests)
    // This needs webhook configured in GitHub
    pollSCM('')

    // Nightly regression at 2 AM on weekdays
    cron('H 2 * * 1-5')
}

Most teams use this combination: webhook for fast smoke feedback on every push, and cron for full regression every night. The empty string in pollSCM enables webhook triggering without actual polling.