Jenkins Pipelines - Pipeline as a code - Difference between Scripted and Declartive Pipelines

Jenkins is an Open source, Java-based automation tool. This tool automates the Software Integration and delivery process called Continuous Integration and Continuous Delivery.

Jenkins support various source code management, build, and delivery tools. Jenkins is #1 Continuous integration tool, especially new features like Jenkins Pipelines (Scripted and Declarative Pipeline) makes the delivery process very easy and help Team to adopt DevOps easily.

Jenkins pipeline

- Pipelines are better than freestyle jobs, you can write a lot of complex tasks using pipelines when compared to Freestyle jobs.
- You can see how long each stage takes time to execute so you have more control compared to freestyle.
- Pipeline is groovy based script that have set of plug-ins integrated for automating the builds, deployment and test execution.
- Pipeline defines your entire build process, which typically includes stages for building an application, testing it and then delivering it.
- You can use snippet generator to generate pipeline code for the stages you don't know how to write groovy code.
- Pipelines are two types - Scripted pipeline and Declarative pipeline

Jenkins Pipeline execution engine supports two DSL syntaxes: Scripted Pipeline and Declarative Pipeline.

Type of Jenkins Pipelines

1. Scripted pipeline
2. Declarative pipeline

 Scripted pipeline

- Scripted pipeline is traditional way of writing pipeline using groovy scripting in Jenkins UI.
- stricter groovy syntax
- each stage can not be executed in parallel in multiple build agents(Slaves) that easily.
- Code is defined within a node block

// Scripted pipeline
node {
  stage('Build') {
       echo 'Building....'
  }
  stage('Test') {
      echo 'Building....'
  }
  stage('Deploy') {
      echo 'Deploying....'
  }
}


Declarative Pipeline (Jenkinsfile)

- New feature added to Jenkins where you create a Jenkinsfile and check in as part of SCM such as Git.
- simpler groovy syntax
- Code is defined within a 'pipeline' block
- each stage can be executed in parallel in multiple build agents(Slaves)

// Declarative pipeline
pipeline {
  agent { label 'slave-node' }
  stages {
    stage('checkout') {
      steps {
        git 'https://bitbucket.org/myrepo''
      }
    }
    stage('build') {
      tools {
        gradle 'Maven3'
      }
      steps {
        sh 'mvn clean test'
      }
    }
  }
}