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:'me@ex.com', subject:'FAILURE:' } finally { deleteDir() }
 } pipeline {
 agent { docker 'ubuntu' } stages {
 stage('Build') {
 steps {
 sh 'mvn clean install'
 }
 }
 }
 post {
 always {
 deleteDir()
 }
 failure {
 mail to:'me@ex.com', subject:'FAILURE:' }
 }
 } Scripted Pipeline Declarative Pipeline

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

No content

No content

No content

No content

No content

No content

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

No content

No content

No content

No content

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

No content

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!

No content

No content

No content

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!