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-actions) - GitHub native CI/CD
kubernetes-ops (kubernetes-ops) - K8s deployment target
docker-management (docker-management) - Container builds

Limitations

Guidance executes against real environments: confirm target, blast radius, and rollback plan before applying anything.
Never deploy to production without explicit approval. Docs-only import: upstream scripts and templates not bundled.

Example

git status && git diff --stat
kubectl diff -f manifest.yaml

Adapted from BagelHole/DevOps-Security-Agent-Skills (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: helper scripts and templates not bundled.