💾Thananjhayan
← Back to notes

The Jenkinsfile Explained

July 14, 2025

The Jenkinsfile lives in the repo root and defines the pipeline as code.

Full pipeline

pipeline {
    agent any
    environment {
        DOCKERHUB_USER  = 'YOUR_DOCKERHUB_USERNAME'
        INDEX_NO        = 'YOUR_INDEX_NO'
        DOCKERHUB_CREDS = credentials('dockerhub-creds')
    }
    stages {
        stage('Checkout') { steps { checkout scm } }

        stage('Build Backend Image') {
            steps { sh 'docker build -f backend2/DOCKERFILE -t $DOCKERHUB_USER/${INDEX_NO}-backend:latest ./backend2' }
        }
        stage('Build Frontend Image') {
            steps { sh 'docker build -f frontend2/DOCKERFILE -t $DOCKERHUB_USER/${INDEX_NO}-frontend:latest ./frontend2' }
        }
        stage('Docker Login') {
            steps { sh 'echo $DOCKERHUB_CREDS_PSW | docker login -u $DOCKERHUB_CREDS_USR --password-stdin' }
        }
        stage('Push Images') {
            steps {
                sh 'docker push $DOCKERHUB_USER/${INDEX_NO}-backend:latest'
                sh 'docker push $DOCKERHUB_USER/${INDEX_NO}-frontend:latest'
            }
        }
    }
    post {
        always  { sh 'docker logout || true' }
        success { echo 'Images built and pushed to Docker Hub.' }
        failure { echo 'Pipeline failed. Check stage logs.' }
    }
}

Commit it to the repo:

git add Jenkinsfile
git commit -m "Add Jenkins pipeline"
git push origin main

What each part means (viva)

  • pipeline { } — the declarative pipeline block.
  • agent any — run on any available Jenkins agent/node.
  • environment { } — define variables; credentials('id') injects secrets safely.
  • stages { } — container for all stages.
  • stage('X') { steps { } } — one phase of the workflow.
  • sh '...' — run a shell command on the agent.
  • checkout scm — pull the repo configured in the job.
  • --password-stdin — pipe the password in without exposing it in logs.
  • post { } — runs after the stages: always, success, failure.

Gotchas

  • The Dockerfile is named DOCKERFILE (caps), so builds must use -f DOCKERFILE.
  • Never hardcode your password — use credentials (see [[jenkins-docker-hub-credentials]]).

For the exam's 3-stage version, see [[jenkins-task3-pipeline]].

💬 Comments