Jenkins

Build, test, and deploy applications using Jenkins, the leading open-source automation server.

When to Use This Skill

Use this skill when:

• Setting up Jenkins pipelines (declarative or scripted)

• Configuring Jenkins agents and executors

• Managing Jenkins plugins and security

• Creating shared libraries for pipeline reuse

• Integrating Jenkins with external tools

Prerequisites

• Jenkins server (2.x or later)

• Admin access to Jenkins

• Java 11+ on Jenkins server

• Basic Groovy understanding for pipelines

Declarative Pipeline

Create Jenkinsfile in repository root:

pipeline { agent any

environment {
    DOCKER_REGISTRY = 'registry.example.com'
    APP_NAME = 'myapp'
}

stages {
    stage('Build') {
        steps {
            sh 'npm ci'
            sh 'npm run build'
        }
    }
    
    stage('Test') {
        steps {
            sh 'npm test'
        }
        post {
            always {
                junit 'test-results/*.xml'
            }
        }
    }
    
    stage('Deploy') {
        when {
            branch 'main'
        }
        steps {
            sh './deploy.sh'
        }
    }
}

post {
    failure {
        mail to: 'team@example.com',
             subject: "Pipeline Failed: ${env.JOB_NAME}",
             body: "Check console output at ${env.BUILD_URL}"
    }
}

}

Agent Configuration

Docker Agent

pipeline { agent { docker { image 'node:20' args '-v /tmp:/tmp' } } stages { stage('Build') { steps { sh 'npm ci && npm run build' } } } }

Kubernetes Agent

pipeline { agent { kubernetes { yaml ''' apiVersion: v1 kind: Pod spec: containers: - name: node image: node:20 command: - sleep args: - infinity - name: docker image: docker:24-dind securityContext: privileged: true ''' } } stages { stage('Build') { steps { container('node') { sh 'npm ci && npm run build' } } } } }

Labeled Agents

pipeline { agent { label 'linux && docker' } stages { stage('Build') { steps { sh 'make build' } } } }

Parameters

pipeline { agent any

parameters {
    string(name: 'BRANCH', defaultValue: 'main', description: 'Branch to build')
    choice(name: 'ENVIRONMENT', choices: ['dev', 'staging', 'prod'], description: 'Target environment')
    booleanParam(name: 'RUN_TESTS', defaultValue: true, description: 'Run tests?')
}

stages {
    stage('Deploy') {
        when {
            expression { params.ENVIRONMENT == 'prod' }
        }
        steps {
            sh "deploy.sh ${params.ENVIRONMENT}"
        }
    }
}

}

Credentials

Using Credentials

pipeline { agent any

environment {
    AWS_CREDS = credentials('aws-credentials')
    DOCKER_CREDS = credentials('docker-hub')
}

stages {
    stage('Deploy') {
        steps {
            withCredentials([
                usernamePassword(
                    credentialsId: 'github-token',
                    usernameVariable: 'GH_USER',
                    passwordVariable: 'GH_TOKEN'
                )
            ]) {
                sh 'git push https://${GH_USER}:${GH_TOKEN}@github.com/repo.git'
            }
        }
    }
}

}

Parallel Stages

pipeline { agent any

stages {
    stage('Tests') {
        parallel {
            stage('Unit Tests') {
                steps {
                    sh 'npm run test:unit'
                }
            }
            stage('Integration Tests') {
                steps {
                    sh 'npm run test:integration'
                }
            }
            stage('E2E Tests') {
                steps {
                    sh 'npm run test:e2e'
                }
            }
        }
    }
}

}

Shared Libraries

Library Structure

vars/ ├── buildApp.groovy ├── deployApp.groovy └── notifySlack.groovy src/ └── com/example/ └── Pipeline.groovy resources/ └── templates/ └── deployment.yaml

Define Shared Step

// vars/buildApp.groovy def call(Map config = [:]) { def nodeVersion = config.nodeVersion ?: '20'

docker.image("node:${nodeVersion}").inside {
    sh 'npm ci'
    sh 'npm run build'
}

}

Use Shared Library

@Library('my-shared-library') _

pipeline { agent any

stages {
    stage('Build') {
        steps {
            buildApp(nodeVersion: '20')
        }
    }
    stage('Deploy') {
        steps {
            deployApp(environment: 'staging')
        }
    }
}

post {
    failure {
        notifySlack(channel: '#builds', status: 'FAILED')
    }
}

}

Scripted Pipeline

node('linux') { try { stage('Checkout') { checkout scm }

    stage('Build') {
        docker.image('node:20').inside {
            sh 'npm ci'
            sh 'npm run build'
        }
    }
    
    stage('Test') {
        sh 'npm test'
    }
    
    if (env.BRANCH_NAME == 'main') {
        stage('Deploy') {
            sh './deploy.sh'
        }
    }
} catch (e) {
    currentBuild.result = 'FAILURE'
    throw e
} finally {
    cleanWs()
}

}

Plugin Management

Essential Plugins

// Install via Jenkins CLI or init.groovy.d def plugins = [ 'workflow-aggregator', // Pipeline 'git', // Git integration 'docker-workflow', // Docker Pipeline 'kubernetes', // Kubernetes agent 'credentials-binding', // Credentials 'blueocean', // Blue Ocean UI 'job-dsl', // Job DSL 'configuration-as-code' // JCasC ]

Configuration as Code

jenkins.yaml

jenkins: systemMessage: "Jenkins configured via JCasC" numExecutors: 2

securityRealm: local: users: - id: admin password: ${ADMIN_PASSWORD}

authorizationStrategy: globalMatrix: permissions: - "Overall/Administer:admin" - "Overall/Read:authenticated"

credentials: system: domainCredentials: - credentials: - usernamePassword: id: "docker-hub" username: "user" password: ${DOCKER_PASSWORD}

Multibranch Pipeline

// Automatically discovers branches with Jenkinsfile // Configure in Jenkins UI: New Item > Multibranch Pipeline

// Branch-specific behavior in Jenkinsfile pipeline { agent any

stages {
    stage('Deploy') {
        when {
            anyOf {
                branch 'main'
                branch 'release/*'
            }
        }
        steps {
            sh './deploy.sh'
        }
    }
}

}

Common Issues

Issue: Pipeline Syntax Errors

Problem: Jenkinsfile fails to parse Solution: Use Pipeline Syntax generator in Jenkins UI, validate with jenkins-cli

Issue: Agent Not Connecting

Problem: Build agents disconnect Solution: Check agent logs, verify network connectivity, increase timeout settings

Issue: Out of Memory

Problem: Jenkins crashes or builds fail with OOM Solution: Increase heap size in JAVA_OPTS , clean up old builds

Best Practices

• Use declarative pipelines for most use cases

• Implement shared libraries for reusable code

• Store Jenkinsfile in source control

• Use credentials plugin for secrets management

• Implement proper cleanup in post blocks

• Configure build retention policies

• Use Blue Ocean for modern UI experience

Related Skills

• github-actions - GitHub native CI/CD

• kubernetes-ops - K8s deployment target

• docker-management - Container builds