Continuous Integration and Continuous Delivery (CI/CD) have become integral to modern software development practices. Jenkins is an open-source platform that serves as an automation server, enabling the implementation of continuous integration and continuous delivery (CI/CD) processes. Our article explains how Jenkins works, its architecture and use cases, and the advantages and disadvantages of using a Jenkins pipeline.
What is Jenkins?
A Java-based open-source automation platform equipped with a plethora of plugins, all designed to facilitate continuous integration. It plays a pivotal role in the software development process, allowing developers and DevOps engineers to seamlessly integrate code changes and enabling consumers to access fresh builds. Moreover, Jenkins empowers organizations to automate and expedite various development lifecycle tasks, including building, testing, documenting, packaging, staging, deploying, and conducting static analysis.
Originally developed as Hudson by Kohsuke Kawaguchi in 2004 while he was at Sun Microsystems (subsequently acquired by Oracle), Jenkins emerged as an open-source solution in the realm of continuous integration. However, a dispute arose between Oracle and the Hudson community following Oracle’s acquisition of Sun Microsystems in 2010.
In 2011, the Hudson community collectively decided to rebrand the project as Jenkins, marking the birth of the “Jenkins” project. Subsequently, Hudson contributed to the Eclipse Foundation, and is no longer under active development. Today, Jenkins is a thriving open-source initiative managed by the CD Foundation, an endeavor under the Linux Foundation.
Jenkins boasts an extensive user base, with over 300,000 installations worldwide, and its popularity is steadily increasing. Organizations leverage Jenkins to expedite their software development processes by automating testing and building procedures at a rapid pace. Jenkins operates as a server-based application and typically relies on web servers like Apache Tomcat for its deployment.
Top Use-Cases of Jenkins
1. Deploy Code into Production
When all the tests designed for a particular feature or release branch pass successfully, a Continuous Integration (CI) system like Jenkins can take the reins and automatically deploy the code to either a staging or production environment. This process is commonly referred to as continuous deployment. It ensures that changes are thoroughly validated before they are merged into the codebase.
To accomplish this, developers often use a dynamic staging environment. After the tests are green, the code is deployed to this dynamic staging environment. From there, it can be further distributed to a centralized staging system, a pre-production environment, or, in some cases, directly to the production environment when the conditions are met.
2. Enabling Task Automation
Jenkins finds valuable applications in the automation of various workflows and tasks. Consider the scenario where a developer is tasked with managing multiple environments, each requiring the installation or upgrade of specific components. In cases where the installation or upgrade process involves a significant number of steps, say exceeding a hundred, executing these tasks manually becomes prone to errors.
Rather than relying on manual intervention, an efficient approach is to leverage Jenkins. With Jenkins, you can meticulously document all the steps necessary to execute the installation or upgrade. This automation significantly reduces the time required to complete the task while minimizing the likelihood of errors during the process.
3. Minimizing the duration required for code review
Jenkins serves as a robust Continuous Integration (CI) system that seamlessly integrates with various DevOps tools. One of its notable functionalities is its ability to notify users when a merge request becomes ready for merging. This typically occurs once all tests have been successfully passed and all other predetermined conditions have been met.
Additionally, the merge request may include insights into code coverage, shedding light on the extent to which the codebase is tested. Jenkins plays a crucial role in expediting the review process for merge requests, effectively reducing the time required by half. Code coverage is determined by assessing the number of lines of code within a component and how many of them are actually executed during testing.
By facilitating efficient merge request handling and offering transparency in the development process, Jenkins significantly enhances collaboration among team members. This ensures that the code review process becomes more streamlined and time-effective.
4. Implementing continuous integration in driving.
Before introducing any changes to software, it’s essential to navigate a complex series of processes. This is where the Jenkins pipeline comes into play, serving as the connective tissue that orchestrates a sequence of events and tasks for achieving continuous integration. Jenkins boasts a versatile collection of plugins that streamline the integration and execution of continuous integration and delivery pipelines. One of the defining characteristics of a Jenkins pipeline is its reliance on the interconnection of tasks and jobs, where each assignment depends on the successful execution of another.
In contrast, continuous delivery pipelines exhibit distinct stages: testing, building, releasing, deploying, and more. These stages are intricately interconnected, forming a cohesive continuum. A continuous delivery (CD) pipeline, therefore, comprises a series of orchestrated events that allow these various stages to function harmoniously.
5. Enhancing code coverage
Jenkins and similar Continuous Integration (CI) servers play a crucial role in code verification, particularly in enhancing test coverage. As tests run and succeed, they contribute to an improvement in code coverage metrics. This approach promotes a culture of openness and accountability within the development team.
The test results are prominently displayed within the build pipeline, serving as a visible reminder for team members to adhere to established guidelines. Much like the principles of code review, the practice of achieving comprehensive code coverage ensures that testing is a transparent and inclusive process accessible to all team members.
6. Improving the code efficiency
Jenkins plays a pivotal role in significantly enhancing the efficiency of the software development process. For instance, it can transform a command prompt code operation into a straightforward GUI button click, all thanks to its automation capabilities. This is achieved by encapsulating the script within a Jenkins task. Additionally, Jenkins offers the flexibility to parameterize tasks, enabling customization and user input. This level of automation can lead to substantial savings in code volume, often replacing hundreds of lines of manual scripting.
Furthermore, Jenkins offers support for manual testing when it’s necessary, all without the need to switch between different environments. It’s a common scenario that code, when hosted locally, may not seamlessly transition to a central system in a private or public cloud due to changes that occur during the transition process. However, Jenkins’ continuous integration capabilities provide a solution. It allows for manual testing, which involves comparing the code to the current state of a production-like environment, ensuring that it remains consistent throughout the development lifecycle.
The components of Jenkins collaborate and function in the following manner:
• Developers make adjustments to the source code, submitting their changes to the repository, and Jenkins generates a fresh build to accommodate the latest Git commit.
• Jenkins can operate in either “push” or “pull” mode. The Jenkins CI server can be initiated by an event, such as a code commit, or it can perform periodic checks on the repository for any updates.
• The build server compiles the code and produces an artifact. In the event of a failed build, the developer will be notified.
• Jenkins is responsible for deploying the compiled application or executable onto the test server, enabling the execution of continuous and automated tests. In the event that developers’ modifications affect the functionality, notifications are sent to alert them.
• Jenkins, when appropriate, carries out deployments to the production server in the absence of any code-related problems.
How does Jenkins operate?
Jenkins can serve as a robust server across a variety of operating systems, including Windows, macOS, Unix variants, and, notably, Linux. It relies on the Oracle JRE or OpenJDK and mandates a Java 8 virtual machine or newer. Typically, Jenkins operates as a Java servlet within a Jetty application server. However, other Java application servers like Apache Tomcat can also host it.
Recently, Jenkins has been adapted to run within a Docker container, providing even more deployment flexibility. It’s available in different forms, including a Web Application Resource (WAR) archive, installation packages tailored for major operating systems, Homebrew packages, Docker images, and access to the source code.
Jenkins’ core source code is primarily written in Java, with some components in Groovy, Ruby, and Antlr. It can be run as a standalone instance or as a servlet within a Java application server like Tomcat. In either configuration, Jenkins offers a web-based user interface and accepts requests through its REST API. Upon initial setup, Jenkins creates an administrator account with a long, unique password, which you’ll need to input during the initial site access. Note that read-only Jenkins images can be found in the Docker Hub online repository.
Furthermore, Jenkins configurations are stored locally in a Jenkinsfile, which is a plain text file. The Jenkinsfile employs a curly bracket syntax reminiscent of JSON. Pipeline steps are enclosed in curly brackets and defined as commands with associated arguments. The Jenkins server interprets the Jenkinsfile and executes the specified tasks, transitioning code from source code commits to runtime in a production environment.
Jenkins files can be generated using a graphical user interface (GUI) or manually crafted through code. This automation covers the entire development lifecycle, from integration to deployment. Every code change committed by a developer triggers a build process.
Typically, these commits are directed to a development branch. Before promoting the build to production, Jenkins can deploy it to an environment suitable for user acceptance testing (UAT). To achieve continuous delivery (CD), these UAT tests may be automated using tools such as Selenium.
If the automated tests pass successfully, the code can be merged into the main branch, where a “golden” build is generated and can be deployed into production without manual intervention. Companies like Amazon, Facebook, and Google serve as prime examples of those achieving 100% continuous delivery, often deploying to production multiple times each day.
Pipelines are needed to run Jenkins. A pipeline is a set of steps the Jenkins server will execute to complete the CI/CD process’s necessary tasks. In the context of Jenkins, a pipeline refers to a collection of jobs (or events) connected in a specific order. It is a collection of plugins that allow the creation and integration of Continuous Delivery pipelines in Jenkins.
The ‘Pipeline Domain-Specific Language (DSL)’ syntax also presents an array of instruments for conceptualizing rudimentary and intricate delivery pipelines as though they were code. Each chore within the Jenkins pipeline fundamentally relies on one or more occurrences in a certain fashion. Jenkins Pipelines encompass a robust technology, encompassing a spectrum of utilities for the hosting, supervision, compilation, and examination of code or modifications to code, spanning across diverse tools like Continuous Integration servers (Bamboo, Jenkins, TeamCity, CruiseControl, and others), Source Control software (e.g., SVN, CVS, Mercurial, GIT, ClearCase, Perforce, and others), Build utilities (Make, Ant, Ivy, Maven, Gradle, and others), as well as Automation testing frameworks (Appium, Selenium, UFT, TestComplete, and others).
The Jenkins pipeline represents a continuous delivery framework initiated by end-users. Within this paradigm, an assemblage of plugins facilitates distinct phases, ranging from version control to user-oriented delivery.
This is important since, before being released, all software modifications and commits go through a lengthy procedure. The method has three phases: automated building, multi-step testing, and deploying procedures. There are two methods to construct a pipeline in Jenkins: directly define the pipeline using the user interface or create a Jenkinsfile using the pipeline as a code technique. The pipeline process is described in a text file that employs Groovy-compatible syntax. Before constructing a Jenkins pipeline, here are the key terminologies to understand: Change this to avoid plagiarism
Jenkins relies on pipelines to execute its tasks effectively. A pipeline represents a sequence of steps that the Jenkins server performs to fulfill the necessary tasks in the CI/CD process. In Jenkins’ terminology, a pipeline is essentially a series of interconnected jobs or events arranged in a specific order. It functions as a collection of plugins that enable the creation and integration of Continuous Delivery pipelines within Jenkins.
The ‘Pipeline Domain-Specific Language (DSL)’ syntax serves as a set of tools for modeling both simple and intricate delivery pipelines in the form of code. Every task within a Jenkins pipeline depends on one or more events in a cohesive manner.
Jenkins Pipelines encompass a robust technology stack that facilitates hosting, monitoring, compilation, and testing of code or code modifications across a wide array of tools, including:
- Continuous integration servers (such as Bamboo, Jenkins, TeamCity, and CruiseControl, among others)
- Source control software (e.g., SVN, CVS, Mercurial, GIT, ClearCase, Perforce, and more)
- Build tools (Make, Ant, Ivy, Maven, Gradle, and others)
- Automation testing frameworks (such as Appium, Selenium, UFT, TestComplete, and similar tools)
The Jenkins pipeline represents a user-defined continuous delivery approach. It integrates multiple plugins that streamline various stages, starting from version control and culminating in user-facing delivery. This holds significance because all software changes and commits undergo an extensive process before being released, comprising three primary phases: automated building, multi-step testing, and deployment procedures.
Constructing a pipeline in Jenkins can be accomplished in two ways: through direct definition using the user interface or by creating a Jenkinsfile using the pipeline-as-code technique. The pipeline process is articulated in a text file that employs a syntax compatible with Groovy. To embark on creating a Jenkins pipeline, it’s essential to grasp the key terminologies involved.
Advantages and Disadvantages of Jenkins
Here are some of the primary benefits of using Jenkins:
- Extensive Plugin Ecosystem: Jenkins boasts a vast array of available plugins, contributing to its adaptability and the ability to create complex, customized pipelines.
- Reliability and Scalability: Jenkins has a solid track record of reliability and can handle various workloads, making it suitable for both small-scale and large-scale deployments.
- Proven and Well-Established: Jenkins has been in use for a long time and has undergone extensive testing and improvement in real-world scenarios.
- Multi-Cloud Support: It can seamlessly integrate with hybrid and multi-cloud environments, making it a versatile choice for diverse infrastructures.
- Robust Documentation and Community Support: Jenkins benefits from a wealth of documentation and a strong community, making it easier for users to find solutions and assistance.
- Java Foundation: It is based on Java, which is a widely used enterprise programming language, making it compatible with legacy enterprise environments.
On the flip side, Jenkins does have its drawbacks:
- Single Server Architecture: Jenkins relies on a single-server architecture, limiting its scalability and potentially causing performance issues in large-scale setups.
- Jenkins Sprawl: The lack of server-to-server federation can lead to the proliferation of standalone Jenkins servers, making management challenging.
- Outdated Java Technologies: Jenkins uses older Java technologies like Servlet and Maven, which may not align with modern Java developments.
- Container Challenges: While it supports containers, Jenkins was not designed with container and Kubernetes environments in mind, lacking nuanced support for these technologies.
- Complex Pipeline Development: Building complex pipelines in Jenkins requires coding in a declarative or scripting language, which can be complex and challenging to debug and maintain.
- Lack of Built-in Deployment Functionality: Jenkins does not offer native functionality for production deployments, necessitating the creation of custom deployment scripts.
- Deployment Complexity: Deploying Jenkins itself can be intricate and may not be easily automated, often requiring additional configuration management tools.
- Plugin Management Complexity: Jenkins boasts a vast number of plugins, which can be overwhelming to navigate. Plugin dependencies and potential conflicts can add to the management burden.
- Groovy Expertise Requirement: Jenkins uses Groovy for programmatic pipelines, which may require users to learn a less commonly used language, potentially making script development more challenging.
In conclusion, Jenkins remains a fundamental tool in the realm of continuous integration and continuous delivery (CI/CD). Its extensive plugin ecosystem, reliability, and community support make it a solid choice for many organizations seeking automation solutions. However, it’s important to consider its limitations, such as the single-server architecture, the complexity of managing plugins, and the need for custom scripting for deployment.
When implementing Jenkins, it’s essential to assess your specific needs and infrastructure. While Jenkins has been the go-to choice for years, newer CI/CD solutions that are more container-native and aligned with modern DevOps practices have emerged. Organizations should carefully evaluate their requirements and consider whether Jenkins or a more contemporary alternative better suits their goals.
In the dynamic world of software development, staying updated on CI/CD tools like Jenkins is vital. Payoda offers strategic consultations to help you navigate this landscape. We provide insights to streamline your software delivery pipelines and boost development processes. Choose Payoda for expert guidance.
Authored by: Yashwanth Subramanian