Chapter 80: DevOps Projects Part 10: Jenkins Agents Freestyle Pipeline Webhook Sonar ECR EKS Approval Libraries Backup

80.3 Project 69: Declarative Jenkinsfile pipeline

By Ravindra Bagale Last updated: 28 October 2026

Friends, code reviews need the pipeline in git. Today we write a Declarative Jenkinsfile with stages, agent labels, post actions, and a Multibranch tip.

What you will build in this project

Write a Declarative Jenkinsfile.
Add Checkout Test Package stages.
Use agent labels and post always.
Create a Pipeline job that points at the file.

1. Start from a real company story

At Wipro in Hyderabad, freestyle clicks differed per team and a release used the wrong Maven goals.

Rough cost: about ₹15 lakh in rollback and customer credits.

Ananya moved every service to a Jenkinsfile in the repo.

Today we write that Declarative file.

Picture 1: git Jenkinsfile → Pipeline job → stages Checkout/Test/Package → post

Ravindra Bagale's Tip

Students put credentials as plain environment strings in the Jenkinsfile. Use credentials() helpers. Keep that habit.

2. Start and prepare

Step 1: Why Jenkinsfile

Why: UI clicks are not reviewable. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: echo why. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 1: a1

Type this:

echo 'Jenkinsfile in git = reviewable pipeline as code'

You will see:

Jenkinsfile in git = reviewable pipeline as code

What it means: Why.

Example 2: a2

Type this:

mkdir -p /tmp/jen69/repo && ls /tmp/jen69

You will see:

repo

What it means: Folder.

Example 3: a3

Type this:

echo 'Today: Declarative stages, label, post, Pipeline job'

You will see:

Today: Declarative stages, label, post, Pipeline job

What it means: Scope.

Step 2: Skeleton file

Why: pipeline block. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: printf Jenkinsfile. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 4: b1

Type this:

printf '%s\n' 'pipeline {' '  agent { label \'maven\' }' '  options { timestamps() }' '  stages {' '    stage(\'Checkout\') {' '      steps { checkout scm }' '    }' '  }' '}' > /tmp/jen69/repo/Jenkinsfile && head -8 /tmp/jen69/repo/Jenkinsfile

You will see:

agent { label 'maven' }

What it means: Skeleton.

Example 5: b2

Type this:

wc -l /tmp/jen69/repo/Jenkinsfile

You will see:

9 /tmp/jen69/repo/Jenkinsfile

What it means: Lines.

Example 6: b3

Type this:

echo 'Declarative starts with pipeline { ... } — not node {'

You will see:

Declarative starts with pipeline { ... } — not node {

What it means: Syntax tip.

Step 3: Test stage

Why: mvn test. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: add stage. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 7: c1

Type this:

printf '%s\n' '    stage(\'Test\') {' '      steps {' '        sh \'mvn -B test\'' '      }' '    }' >> /tmp/jen69/repo/Jenkinsfile && tail -6 /tmp/jen69/repo/Jenkinsfile

You will see:

sh 'mvn -B test'

What it means: Test stage.

Example 8: c2

Type this:

echo 'Use sh on Linux agents; bat on Windows agents'

You will see:

Use sh on Linux agents; bat on Windows agents

What it means: Shell tip.

Example 9: c3

Type this:

echo 'Fail the stage if tests fail — default Maven behaviour'

You will see:

Fail the stage if tests fail — default Maven behaviour

What it means: Fail.

3. Build the main pieces

Step 4: Package stage

Why: mvn package. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: add stage. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 10: d1

Type this:

printf '%s\n' '    stage(\'Package\') {' '      steps {' '        sh \'mvn -B -DskipTests package\'' '      }' '    }' >> /tmp/jen69/repo/Jenkinsfile && grep Package /tmp/jen69/repo/Jenkinsfile

You will see:

stage('Package') {

What it means: Package.

Example 11: d2

Type this:

echo 'skipTests here only because Test stage already ran'

You will see:

skipTests here only because Test stage already ran

What it means: Why skip.

Example 12: d3

Type this:

echo 'Never skip tests globally without a Test stage above'

You will see:

Never skip tests globally without a Test stage above

What it means: Habit.

Step 5: Post actions

Why: always and success. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: close stages and post. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 13: e1

Type this:

printf '%s\n' '  }' '  post {' '    always { junit \'target/surefire-reports/*.xml\' }' '    success { archiveArtifacts artifacts: \'target/*.jar\', fingerprint: true }' '    cleanup { cleanWs() }' '  }' '}' >> /tmp/jen69/repo/Jenkinsfile && tail -8 /tmp/jen69/repo/Jenkinsfile

You will see:

success { archiveArtifacts artifacts: 'target/*.jar', fingerprint: true }

What it means: Post.

Example 14: e2

Type this:

echo 'always runs on success and failure'

You will see:

always runs on success and failure

What it means: Always.

Example 15: e3

Type this:

echo 'cleanup keeps agents from filling disks'

You will see:

cleanup keeps agents from filling disks

What it means: Cleanup.

Step 6: Pipeline job

Why: Point at SCM. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: job tip. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 16: f1

Type this:

printf '%s\n' 'New Item -> Pipeline' 'Name: cart-pipeline' 'Definition: Pipeline script from SCM' 'Script Path: Jenkinsfile' > /tmp/jen69/JOB.txt && cat /tmp/jen69/JOB.txt

You will see:

Script Path: Jenkinsfile

What it means: Job.

Example 17: f2

Type this:

echo 'SCM URL = your cart repo; credentials from Jenkins store'

You will see:

SCM URL = your cart repo; credentials from Jenkins store

What it means: SCM.

Example 18: f3

Type this:

echo 'Build Now should paint stage boxes green'

You will see:

Build Now should paint stage boxes green

What it means: Expect.

4. Automate and verify

Step 7: Blue Ocean tip

Why: Stage view. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: read the UI. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 19: g1

Type this:

echo 'Open the run -> Pipeline Steps to see each sh'

You will see:

Open the run -> Pipeline Steps to see each sh

What it means: UI.

Example 20: g2

Type this:

echo 'Stage View plugin shows a grid of past runs'

You will see:

Stage View plugin shows a grid of past runs

What it means: Grid.

Example 21: g3

Type this:

printf '%s\n' 'Acceptance: Checkout Test Package all green' > /tmp/jen69/ACCEPT.txt && cat /tmp/jen69/ACCEPT.txt

You will see:

Acceptance: Checkout Test Package all green

What it means: Gate.

Step 8: Multibranch tip

Why: One job many branches. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: notes. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 22: h1

Type this:

printf '%s\n' 'Multibranch Pipeline scans branches for Jenkinsfile' 'PR builds appear as separate jobs' > /tmp/jen69/MULTIBRANCH.txt && cat /tmp/jen69/MULTIBRANCH.txt

You will see:

Multibranch Pipeline scans branches for Jenkinsfile

What it means: MB.

Example 23: h2

Type this:

echo 'Discover branches strategy: exclude branches without Jenkinsfile'

You will see:

Discover branches strategy: exclude branches without Jenkinsfile

What it means: Discover.

Example 24: h3

Type this:

echo 'Webhook project 70 will trigger scans automatically'

You will see:

Webhook project 70 will trigger scans automatically

What it means: Bridge.

Step 9: Credentials tip

Why: No plain secrets. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: withCredentials. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 25: i1

Type this:

echo 'withCredentials([string(credentialsId: \'sonar-token\', variable: \'SONAR_TOKEN\')]) { sh \'echo token length ${#SONAR_TOKEN}\' }'

You will see:

withCredentials([string(credentialsId: 'sonar-token', variable: 'SONAR_TOKEN')]) { sh 'echo token length ${#SONAR_TOKEN}' }

What it means: Helper.

Example 26: i2

Type this:

echo 'Mask passwords in console — Jenkins does this for credentials bindings'

You will see:

Mask passwords in console — Jenkins does this for credentials bindings

What it means: Mask.

Example 27: i3

Type this:

echo 'Never printf a secret in a shared library either'

You will see:

Never printf a secret in a shared library either

What it means: Habit.

5. Harden and accept

Step 10: Story Wipro

Why: Hyderabad freestyle drift. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: story. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 28: j1

Type this:

printf '%s\n' 'At Wipro in Hyderabad, freestyle clicks differed per team and a release used wrong Maven goals.' 'Ananya moved every service to a Jenkinsfile in the repo.' > /tmp/jen69/STORY.txt && wc -l /tmp/jen69/STORY.txt

You will see:

2 /tmp/jen69/STORY.txt

What it means: Story.

Example 29: j2

Type this:

echo 'Rough cost: about ₹15 lakh in rollback and customer credits'

You will see:

Rough cost: about ₹15 lakh in rollback and customer credits

What it means: Cost.

Example 30: j3

Type this:

echo 'Ananya: PASS'

You will see:

Ananya: PASS

What it means: Sign-off.

Step 11: Proof

Why: Jenkinsfile exists. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: grep stages. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 31: k1

Type this:

grep stage /tmp/jen69/repo/Jenkinsfile

You will see:

stage('Checkout') {\n    stage('Test') {\n    stage('Package') {

What it means: Stages.

Example 32: k2

Type this:

test -f /tmp/jen69/ACCEPT.txt && echo 'accept ok'

You will see:

accept ok

What it means: accept.

Example 33: k3

Type this:

echo 'Next: SCM webhook auto-build project 70'

You will see:

Next: SCM webhook auto-build project 70

What it means: Bridge.

Step 12: Acceptance

Why: Pipeline green from Jenkinsfile. We do this before the next step so mistakes stay small and easy to undo. Read the output carefully; the numbers and names tell you if the machine is healthy.

What: final. Follow the numbered examples below. Type each command, read the exact output, and match the meaning line before you move on. That is how real teams learn a tool.

Example 34: z1

Type this:

echo 'Declarative file in git'

You will see:

Declarative file in git

What it means: File.

Example 35: z2

Type this:

echo 'Three stages green'

You will see:

Three stages green

What it means: Stages.

Example 36: z3

Type this:

echo 'JAR archived on success'

You will see:

JAR archived on success

What it means: Artifact.

Check yourself

Q1. Who fixed Wipro freestyle drift?

Ananya

Q2. File name?

Jenkinsfile

Q3. Syntax?

Declarative

Q4. Agent key?

label

Q5. Post block?

always

Q6. Secrets in env plain?

Friends, you ran a Declarative Jenkinsfile pipeline. Did you understand? Let us try it once more. Add a stage named Quality that echoes a Sonar tip and keep the pipeline green.

Lab: try at home

Write Jenkinsfile.
Create Pipeline job.
Run and archive.
Note Multibranch next step.

Recap

Pipeline as code.
Stages are readable.
Labels pick agents.
Post always cleans.
No plain secrets.