04_build_triggers.md

Lab 4: Build Trigger

Like build options/properties triggers need to be configured in the Jenkinsfile for multibranch jobs. In this lab we add a SCM polling trigger and a cron trigger to our job.

Lab 4.1: Build Trigger

In declarative pipelines build triggers are configured through the triggers directive. Only a single triggers directive is allowed and must be contained in the pipeline block. Create a new branch named lab-4.1 from branch lab-3.1 and change the contents of the Jenkinsfile to:

pipeline {
    agent any
    options {
        buildDiscarder(logRotator(numToKeepStr: '5'))
        timeout(time: 10, unit: 'MINUTES')
        timestamps()  // Requires the "Timestamper Plugin"
    }
    triggers {
        pollSCM('H/5 * * * *')
    }
    stages {
        stage('Greeting') {
            steps {
                echo 'Hello, World!'
            }
        }
    }
}

A cronlike repetitive execution can be configured as followed:

triggers {
    cron('@midnight')
}

H in a cron expression stands for hash (of the job name) and is used to prevent load spikes on Jenkins by distributing job triggering evenly over the configured range. @midnight also makes use of hashing and actually means some time between 12:00 AM and 2:59 AM. The exact times your job was triggered last and will be triggered next are shown under "View Configuration."
For more info regarding Jenkins cron expressions see http://www.scmgalaxy.com/tutorials/setting-up-the-cron-jobs-in-jenkins-using-build-periodically-scheduling-the-jenins-job.

Note: Verify on the Jenkins master, whether the new triggers are now visible in the configuration view.

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End of Lab 4

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