Writing a Jenkinsfile

A Jenkinsfile is a text file, committed to your repository, that describes your entire pipeline. This is pipeline as code: the build process gets reviewed in pull requests, versioned alongside the app, and never lives only in someone's memory of how the Jenkins UI was clicked through.

Declarative pipeline shape

The most common style is the declarative pipeline - a structured block that reads almost like a checklist:

pipeline {
  agent any

  stages {
    stage('Build') {
      steps {
        sh 'npm install'
        sh 'npm run build'
      }
    }
    stage('Test') {
      steps {
        sh 'npm test'
      }
    }
    stage('Deploy') {
      steps {
        sh './deploy.sh'
      }
    }
  }

  post {
    failure {
      echo 'Pipeline failed - notify the team'
    }
  }
}

Reading it piece by piece

• agent any - run this pipeline on whichever available agent Jenkins picks.
• stages - the ordered list of phases. Each stage shows up as its own box in the Jenkins UI, so you can see exactly which one failed.
• steps - the actual shell commands (sh '...') that do the work inside a stage.
• post - runs after everything else, regardless of outcome - the natural place for notifications, cleanup, or artifact archiving.

Why the file lives in your repo

Because the Jenkinsfile travels with the code, a pull request that changes the test command, or adds a new deployment step, is reviewed exactly like any other code change - no separate "go click this setting in Jenkins" step that someone inevitably forgets to do.

Create one now:

touch Jenkinsfile

When you're ready, hit Mark complete and move to the next lesson.