Declarative Pipelines Andrew Bayer Arnaud Héritier

Arnaud Héritier • Long time Jenkins user and community member • August 2007 : My first discussion on the mailing list and my first ticket about Jenkins born Hudson 1.131 • Contributor on various plugins: • Maven, Xcode, Appaloosa, … • Member of the Jenkins infra team • I love to reboot confluence ☺ • Support Delivery Manager at CloudBees, Inc • I help our customers to get the best from Jenkins @aheritier aheritier

What is Declarative?

What is Declarative? ● A syntax for Jenkins Pipelines designed to… ○ Have smarter default behavior for most use cases ○ Make Pipelines more structured ○ Provide better error reporting and handling

Smarter default behavior ● Default SCM checkout ● Built with Docker and containers in mind from day one ● No more need for try/catch for notifications, etc ● More intuitive ways to specify job properties, triggers and parameters ● Streamlined syntax for conditional execution of stages

More structure in Pipelines ● Separate configuration from actual steps to be executed ● Everything happens in a stage ● Easier to look at any Declarative Pipeline and understand what it’s doing - more consistency! ● Enables round-tripping with the visual editor (more on this later!) ● Built with and for Blue Ocean visualization

Better error reporting ● Syntax and validation errors reported at the very beginning of the build ● No more waiting til a build has gone an hour to discover that you misspelled “timeout”! ● Errors report as compilation errors, pointing to the specific code or text that’s causing problems

Better error reporting ● Eliminates many potentially confusing stack traces (though not all!) ● Validates things like syntax, required configuration, step parameter types, and more

What happens to Scripted Pipeline? ● In short? Nothing. ● We’re now calling “traditional” Pipeline “Scripted Pipeline” to distinguish it from Declarative Pipeline ● All one execution engine behind the scenes ○ Declarative is built on top of Scripted Pipeline, not replacing it ○ Blue Ocean and Stage View don’t distinguish between a Scripted Pipeline or a Declarative Pipeline

What happens to Scripted Pipeline? ● Scripted Pipeline still used *inside* Declarative Pipeline in steps blocks, post blocks ○ You can copy the contents of a Declarative steps block into a Scripted Pipeline (inside a node block, of course!) and it’ll Just Work.

Why Declarative?

Why everyone should use Pipeline ● Durability ● Pipeline as Code ● More modern backend implementation ● More powerful and flexible than traditional Jenkins jobs

Benefits of Declarative for new users ● Lower barrier of entry than Scripted Pipelines ● Human readable ● Does not require Groovy-specific expertise ● Create and edit Declarative Pipelines via the UI Editor

Benefits of Declarative for existing users ● Uses same engine as Scripted, so existing investments still pay off ● Expand usage and usability ○ Less burden on “experts” ○ Easier empowerment of other users ● Easier collaboration and code review ● Lintable! ● Separation of Jenkins infrastructure-related configuration from steps to execute

Syntax Overview

© 2017 CloudBees, Inc. All Rights Reserved. 16 node { 
 try { stage('Build') { checkout scm docker.image('ubuntu').inside {
 sh 'mvn clean install' } } }
 catch(exc) { mail to:'[email protected]', subject:'FAILURE:' } finally { deleteDir() }
 } pipeline {
 agent { docker 'ubuntu' } stages {
 stage('Build') {
 steps {
 sh 'mvn clean install'
 }
 }
 }
 post {
 always {
 deleteDir()
 }
 failure {
 mail to:'[email protected]', subject:'FAILURE:' }
 }
 } Scripted Pipeline Declarative Pipeline

First example https://gist.github.com/abayer/ bd99a722aeee5077a16c4bfc6ed8f9a1

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Second example https://gist.github.com/abayer/ 01ca97caae06aeb2d8e3f71b3bc0b9a9

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Validation

Validation and linting ● Always happens at the beginning of a build ● If any validation errors are found, the build will fail before actually running anything ● Errors point to the problem area with line/column number and an error message, often with suggestions for what you may have intended

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CLI and API support for linting

Blue Ocean

Blue Ocean visualization ● Some special smarts on both sides for optimized visualization ● Blue Ocean keeps built-in stages for things like checkout, Docker image prep, post-build actions out of your way unless there’s a problem ● Special marking of stages that have been skipped due to either an unsatisfied when condition or an earlier failed stage

Pipeline Visual Editor!

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What’s next?

Declarative - Parallel stages stage('foo') { parallel { stage('first') { steps { echo "First branch" } } stage('second') { steps { echo "Second branch" } } } } https://issues.jenkins-ci.org/browse/JENKINS-41334

That’s a wrap!

Resources on Declarative • Documentation on https://jenkins.io/doc/ • Examples coming soon at https://github.com/ jenkinsci/pipeline-examples • Plugin source at https://github.com/jenkinsci/pipeline- model-definition-plugin

Questions?

Thanks!