Jenkins
The Pillar of Continuous Integration and Continuous Delivery
Introduction
Jenkins is an open-source automation tool that plays a crucial role in the Continuous Integration (CI) and Continuous Delivery (CD) process. Since its inception, Jenkins has been a cornerstone in the DevOps ecosystem, facilitating automatic integration and software delivery. In this article, we will explore Jenkins’ history, purpose, and objectives, and discuss its real-world usage with practical examples and use cases.
History and Purpose
Originally launched as Hudson in 2004, Jenkins was renamed in 2011 after a fork due to disagreements between the developer community and Oracle. Since then, Jenkins has been developed and maintained by the Jenkins community, becoming one of the most popular tools for CI/CD. The primary goal of Jenkins is to facilitate the automation of the software development process, allowing teams to integrate code changes continuously and deliver production-ready versions faster and more reliably. Jenkins automates the building, testing, and deployment of applications, providing quick feedback and helping to identify issues in the code at early stages.
What is CI/CD?
Understanding Jenkins requires a grasp of the CI/CD concepts it supports. Continuous Integration (CI) is a software development practice where developers merge their changes to a central repository frequently, preferably several times a day. Each integration is then verified by an automated build, allowing teams to detect problems quickly. Continuous Delivery (CD) extends the concept of CI by ensuring that code changes can be automatically prepared for a release to production. The goal is to have software always ready for deployment.
Jenkinsfile and Jenkins Pipeline
The core of Jenkins’ functionality in CI/CD is encapsulated in the Jenkins Pipeline, defined through a Jenkinsfile. This file, written in Groovy, defines the stages and steps necessary for building, testing, and deploying the software. Using Jenkinsfile allows pipelines to be versioned alongside the source code, ensuring that CI/CD definitions are replicable and consistent.
A Jenkins Pipeline is a collection of interconnected jobs that model the software delivery process. There are two main types of pipelines in Jenkins: Declarative Pipeline and Scripted Pipeline. Here is an example of each:
Declarative Pipeline:
pipeline {
agent any
stages {
stage('Build') {
steps {
echo 'Building...'
sh 'make'
}
}
stage('Test') {
steps {
echo 'Testing...'
sh 'make test'
}
}
stage('Deploy') {
steps {
echo 'Deploying...'
sh 'make deploy'
}
}
}
}Scripted Pipeline:
node {
stage('Build') {
echo 'Building...'
sh 'make'
}
stage('Test') {
echo 'Testing...'
sh 'make test'
}
stage('Deploy') {
echo 'Deploying...'
sh 'make deploy'
}
}Groovy Script
The use of Groovy scripting in Jenkins Pipelines enables the creation of complex and dynamic workflows. Groovy is a powerful, dynamic scripting language that runs on the Java Virtual Machine (JVM). It allows for flexible and readable syntax that can be integrated with existing Java libraries. By leveraging Groovy, Jenkins Pipelines can adapt to the specific needs of the project, creating a seamless and efficient CI/CD process.
Real-World Usage and Use Cases
The versatility of Jenkins is evident in its widespread adoption by companies like Google, Netflix, and Amazon. These organizations use Jenkins to automate their CI/CD processes, integrating it with various tools and services such as GitHub, Docker, and Kubernetes. For instance, a development team working on a microservices-based web application can configure Jenkins to handle CI by triggering builds and automated tests with each commit to the Git repository. This ensures that new code does not break the existing application. For CD, Jenkins can automatically deploy code to a staging environment for additional testing and quality assurance. Once approved in staging, Jenkins can manage continuous deployment by automatically deploying the code to production, thus reducing delivery time and minimizing human errors.
Jenkins has over 1,500 plugins, allowing integration with various development and operations tools. It can be horizontally scaled using distributed agents, known as main and runner nodes, enabling the parallel execution of multiple jobs. The Jenkins community is one of the most active in the DevOps ecosystem, constantly contributing to the development of new features and improvements.
Practical Example
To illustrate the practical application of Jenkins, consider a pipeline for a Node.js application using Docker:
pipeline {
agent any
environment {
DOCKER_IMAGE = "node:14"
}
stages {
stage('Checkout') {
steps {
checkout scm
}
}
stage('Build') {
steps {
script {
docker.image(DOCKER_IMAGE).inside {
sh 'npm install'
sh 'npm run build'
}
}
}
}
stage('Test') {
steps {
script {
docker.image(DOCKER_IMAGE).inside {
sh 'npm test'
}
}
}
}
stage('Deploy') {
steps {
script {
docker.image(DOCKER_IMAGE).inside {
sh 'npm run deploy'
}
}
}
}
}
}Conclusion
Jenkins is a powerful and flexible tool that has revolutionized how software is developed, tested, and deployed. Its capability for continuous integration and automation allows development teams to deliver high-quality software quickly and efficiently. With an active community and a vast library of plugins, Jenkins remains the preferred choice for CI/CD in companies around the world. If you are looking for a robust tool to improve your development and delivery processes, Jenkins certainly deserves your consideration.
