What is Jenkins? Features and Architecture Explained

Demand for the development of dependable, functional apps has soared in recent years. In a volatile and highly competitive business environment, the systems created to support, and drive operations are crucial. Naturally, organizations will turn to their in-house development teams to deliver the programs, apps, and utilities on which the business counts to remain relevant.

That's a lot to ask from DevOps. Fortunately, there are tools to help deliver custom, quality applications in a timely fashion. Jenkins is one of them. Conjuring images of the stereotypical English butler, the tool acts as a "faithful servant" of sorts, easing cumbersome development tasks.

Let us now begin this article to take a deep dive into what is Jenkins, its features, and architecture.

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Development Before Jenkins

Before the advent of Jenkins, developers had to complete code testing before they could check for errors. Developers on teams, tending to work independently, each created large segments of code to add to the base code. The entire source code would be checked for errors - a time-consuming and challenging undertaking. Multiple developers would each send commits to version control, increasing the time required to identify and fix bugs. There was no iterative code improvement, and the software delivery process was slow.

Let us now explore the topic of what is Jenkins and continuous integration.

What is Jenkins?

Jenkins to the rescue! As a Continuous Integration tool, Jenkins allows seamless, ongoing development, testing, and deployment of newly created code. Continuous Integration is a process wherein developers commit changes to source code from a shared repository, and all the changes to the source code are built continuously. This can occur multiple times daily. Each commit is continuously monitored by the CI Server, increasing the efficiency of code builds and verification. This removes the testers' burdens, permitting quicker integration and fewer wasted resources.

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Why Jenkins?

Jenkins is one of the top DevOps tools because it is free, open-source and modular, and can integrate with pretty much every other DevOps tool out there. There are over a thousand plugins that you can use to extend Jenkins’ capabilities and make it more user-specific. All of these plugins and extensions are developed in Java. This means that Jenkins can also be installed on any operating system that runs on Java.

Jenkins History

Kohsuke Kawaguchi first developed Hudson in 2004 while working at Sun Microsystems. When Oracle acquired Sun Microsystems in 2010, there was a dispute between Oracle and the Hudson community with respect to the infrastructure used. There was a call for votes to change the project name from Hudson to Jenkins, which was overwhelmingly approved by the Hudson community on January 29, 2011, thereby creating the first “Jenkins” project.

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Jenkins Architecture

Here's how Jenkins elements are put together and interact:

• Developers commit changes to the source code, found in the repository.
• The Jenkins CI server checks the repository at regular intervals and pulls any newly available code.
• The Build Server builds the code into an executable file. In case the build fails, feedback is sent to the developers.
• Jenkins deploys the build application to the test server. If the test fails, the developers are alerted.
• If the code is error-free, the tested application is deployed on the production server.

The files can contain different code and be very large, requiring multiple builds. However, a single Jenkins server cannot handle multiple files and builds simultaneously; for that, a distributed Jenkins architecture is necessary.

Now you can understand the Master-Slave architecture in this What is Jenkins article.

Jenkins Master-Slave Architecture

As you can see in the diagram provided above, on the left is the Remote source code repository. The Jenkins server accesses the master environment on the left side and the master environment can push down to multiple other Jenkins Slave environments to distribute the workload. 

That lets you run multiple builds, tests, and product environment across the entire architecture. Jenkins Slaves can be running different build versions of the code for different operating systems and the server Master controls how each of the builds operates.

Supported on a master-slave architecture, Jenkins comprises many slaves working for a master. This architecture - the Jenkins Distributed Build - can run identical test cases in different environments. Results are collected and combined on the master node for monitoring.

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Jenkins Applications

Jenkins is a popular open-source automation server that provides a robust platform for implementing continuous integration and continuous delivery (CI/CD) pipelines. Its flexibility and extensive plugin ecosystem allow it to fit into nearly any development workflow, supporting a wide range of use cases across software development and deployment. Here are some detailed applications of Jenkins:

1. Continuous Integration (CI)

Jenkins is primarily used to automate the process of continuous integration, where it builds and tests code every time a change is committed to a version control system. This helps developers detect issues early in the development cycle, improving code quality and reducing the time needed to validate and release new software updates.

• Automated Builds: Jenkins can compile and build code from various environments and languages.
• Automated Testing: It can run a suite of tests (unit, integration, system) on new code to ensure it doesn't break anything.

2. Continuous Delivery (CD)

Beyond continuous integration, Jenkins can automate steps in software delivery, making it easier to deploy and release new versions. It allows for the automation of the deployment process, making sure that you can release reliably at any time.

• Automated Deployment: Jenkins can automate the deployment of applications to various environments, including testing, staging, and production.
• Rollbacks: It can also automate the rollback of a deployment if the deployment fails, ensuring quick recovery from errors.

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3. Infrastructure as Code (IaC)

Jenkins is used to implement Infrastructure as Code practices, which involve managing and provisioning infrastructure through code instead of through manual processes.

• Configuration Management: Jenkins can integrate with tools like Ansible, Chef, and Puppet to automate the configuration of servers.
• Server Provisioning: It can also use scripts or templates to create or update servers.

4. Monitoring and Reporting

Jenkins can be configured to monitor its own performance and to generate reports on various aspects of the development process.

• Build Monitoring: Jenkins can keep track of build success rates and notify developers of failures.
• Performance Trends: It can generate reports that track performance metrics over time, helping teams understand trends.

5. DevOps and Multibranch Pipeline

Jenkins supports DevOps practices by enabling teams to implement multibranch pipelines, where each branch of the version control system can have its own tailored CI/CD pipeline.

• Pipeline as Code: Jenkins Pipelines allow defining build, test, and deploy stages that are stored in a Jenkinsfile and versioned along with the code.
• Parallel Execution: Jenkins can execute jobs in parallel, reducing the time required for builds and tests.

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6. Containerization Support

Jenkins has robust support for Docker and Kubernetes, allowing teams to use containers for builds, tests, and deployments.

• Docker Integration: Jenkins can build Docker images and push them to Docker registries.
• Kubernetes Integration: It can manage Kubernetes pods, enabling dynamic provisioning of agents for builds and tests.

7. Third-Party Integration

Jenkins' extensive plugin ecosystem allows it to integrate with virtually any tool used in software development, from version control systems like Git to issue tracking systems like JIRA, and artifact repositories like Artifactory.

8. Security and Compliance

Jenkins can help enforce security policies and compliance standards by automating security scans and compliance checks.

• Static Code Analysis: Plugins can scan source code for security vulnerabilities.
• Compliance Checks: Jenkins can run scripts or tools that check compliance with various standards.

What are the Jenkins Features?

Jenkins offers many attractive features for developers:

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  Easy Installation

  Jenkins is a platform-agnostic, self-contained Java-based program, ready to run with packages for Windows, Mac OS, and Unix-like operating systems.

• Easy Configuration

  Jenkins is easily set up and configured using its web interface, featuring error checks and a built-in help function.

• Available Plugins

  There are hundreds of plugins available in the Update Center, integrating with every tool in the CI and CD toolchain.

• Extensible

  Jenkins can be extended by means of its plugin architecture, providing nearly endless possibilities for what it can do.

• Easy Distribution

  Jenkins can easily distribute work across multiple machines for faster builds, tests, and deployments across multiple platforms.

• Free Open Source

  Jenkins is an open-source resource backed by heavy community support.

As a part of our learning about what is Jenkins, let us next learn about the Jenkins architecture.

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Advantages of Using Jenkins

Jenkins is a powerful tool truly built and friendly for developers. Here are some of the most significant advantages of using Jenkins:

1. Free to Use

Jenkins is fully open-source and free to use. Since its development in 2011, it is the most preferred CI/CD tool used by developers in both early-stage startups and big organizations.

2. Rich Plugin Ecosystem

There are over a thousand different plugins that can be used to enhance the functionality of a Jenkins environment and suit the specific needs of an organization.

3. Easy Integration 

Jenkins can be easily integrated with a number of popular cloud platforms such as Google Cloud, Digital Ocean, Amazon EC2 and more.

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Disadvantages of Using Jenkins

Jenkins also has its own share of disadvantages. Here are some of the most common ones:

1. Developer Centric

Jenkins is more developer-centric and feature-driven. A person may need to have some sort of developer experience to use Jenkins.

2. Setting Change Issues

There are some issues (such as Jenkins not starting up) that you may face when you change the settings in Jenkins. These issues can come up when you install some plugins as well. Fortunately, Jenkins has a large user base so you can search online for a solution whenever you are faced with these issues.

The Bottom Line

Jenkins provides developers with an excellent framework from which they can develop and test new codes, resulting in the faster delivery of better quality software. By avoiding costly delays and log jams, developers can become an organization's MVPs.

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Earn Your Certification

Knowing what is Jenkins isn’t enough, if you're eager to get skilled in the fundamentals of Jenkins and how to continually implement and deploy codes in a DevOps environment, you can enroll for the DevOps Engineer Masters Program and learn to integrate automated tests to verify the build pipelines and set up code quality reporting. You can even get skilled in server automation, continuous integration, continuous deployment, build pipelines, and more.