Introduction to
Jenkins

Manage Jenkins → Plugins → Installed, filtered to "pipeline" (local Jenkins 2.580.1). Docs: Managing plugins

Dashboard: every job, its last result (S), a "weather" icon for recent stability (W), last success/failure and duration. The deck's demo jobs are the Intro_* rows.

New Item: pick a job type. Pipeline for one Jenkinsfile; Multibranch Pipeline for one job per branch/PR; Freestyle is the classic form-driven job.

Configure → Pipeline for job Intro_params_and_post: an inline script, run in the Groovy sandbox.

Declarative ran: Intro_declarative #1

pipeline {
    agent any
    stages {
        stage('Build') {
            steps { sh 'echo building' }
        }
        stage('Test') {
            steps {
                script {
                    for (n in ['unit', 'smoke']) {
                        sh "echo running ${n} tests"
                    }
                }
            }
        }
    }
    post {
        always { echo 'cleanup' }
    }
}

Scripted ran: Intro_scripted #1

node {
    try {
        stage('Build') {
            sh 'echo building'
        }
        stage('Test') {
            for (n in ['unit', 'smoke']) {
                sh "echo running ${n} tests"
            }
        }
    } finally {
        echo 'cleanup'
    }
}

Time and polling ran once; schedules not waited for

pipeline {
    agent any
    triggers {
        cron('H 2 * * 1-5')          // nightly, Mon-Fri; H spreads the start minute
        pollSCM('H/15 * * * *')      // poll the repo every 15 min (webhooks are better)
    }
    stages {
        stage('Nightly') {
            steps { echo 'nightly build' }
        }
    }
}

Branch conditions and more post linter only

pipeline {
    agent { label 'linux' }
    stages {
        stage('Release') {
            when { branch 'main' }
            steps { echo 'only on main' }
        }
    }
    post {
        fixed   { echo 'back to green' }
        cleanup { deleteDir() }
    }
}

Stage View (Pipeline: Stage View plugin) on the job page: one row per build, one column per stage, with timings. #3 is red from Test onwards.

Pipeline Graph View (/job/NAME/N/stages) of Intro_params_and_post #3: the parallel Checks fan out, with each step's log beneath.

Manage Jenkins → Credentials: IDs and descriptions only; values are never shown again after saving.

Correct (single quotes, the Upload stage in Declarative Anatomy): the shell expands $TOKEN; the log prints ****.

Insecure: sh "echo token=${TOKEN}" (double quotes) expands the secret in Groovy before the command reaches the agent: it is copied into the process arguments (visible with ps), and any shell metacharacters in it run. Jenkins warns; the fix is single quotes. See String interpolation.

The job page after five builds: the archived tarball (with its fingerprint) and the Test Result Trend: 3 tests, then 4 with one failure at #3, then 4 passing.

Build #3's test report: test_mean_of_empty_list failed (age 1: it failed for the first time in this build).

When ten repos copy the same 80 lines of Jenkinsfile, move them into a shared library: a Git repo of Groovy that pipelines load by name.

my-library/
├── vars/          # global steps: vars/greet.groovy → greet()
│   └── greet.groovy
├── src/           # Groovy classes (org/acme/Build.groovy)
└── resources/     # files read with libraryResource

vars/greet.groovy

// A custom step: any pipeline that loads the library can call  greet 'name'
def call(String name = 'world') {
    echo "Hello, ${name}, from the shared library"
}

Using it ran: Intro_shared_library #1

@Library('intro-lib') _

pipeline {
    agent any
    stages {
        stage('Greet') {
            steps { greet 'Jenkins' }
        }
    }
}

Loading library intro-lib@main:demo/shared-lib/
Hello, Jenkins, from the shared library

Docs: Extending with shared libraries. A bigger example drives SimEng 07's regressions.

Blue Ocean was a redesigned UI for pipelines (visual graph, PR-centric views, a pipeline editor). Many tutorials still show it.

Source: jenkins.io/doc/book/blueocean. Plugin status changes; check the page before deciding.

From the WAR file how this deck's Jenkins runs

# needs a supported Java (this deck: JDK 21)
java -jar jenkins.war --httpListenAddress=127.0.0.1 --httpPort=8080
# first start prints an initial admin password, also in
#   $JENKINS_HOME/secrets/initialAdminPassword

With Docker not run here: no Docker on this PC

docker run -p 8080:8080 -p 50000:50000 \
  -v jenkins_home:/var/jenkins_home jenkins/jenkins:lts-jdk21

Port 50000 is for inbound agents. Docs: WAR file, Docker, Java support policy. Image tags change; check Docker Hub.