What is Jenkins? History, Architecture, Pipeline & Benefits

For teams that are willing to integrate the different stages of DevOps, they can do it through continuous integration. There are several tools available to help perform this integration. One of the most popular ones out of them is Jenkins. However, before you jump the gun and start to put this tool to work, you must understand what it exactly is, how it works, what features it comes with, and what advantages it offers over other similar tools. 

When Jenkins was launched, it was just an open-source continuous integration tool. However, after recent updates, it has become a tool that is capable of performing two jobs – continuous integration and continuous delivery. It is now a tool that helps in organizing application deployment as well. This blog intends to cover all the details that you should know about Jenkins before you start using it in your IT projects. 

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History of Jenkins

Just like we have so many interesting stories about the development of so many technologies and tools over the years, we have one for Jenkins, too. It goes back to 2004, Kohsuke Kawaguchi, the developer of Jenkins, was working with Sun Microsystems as a Java developer. 

Little did Kawaguchi know that the future had something very special in store for him. At that time, Kawaguchi was involved in several development projects. He didn’t like breaking the builds due to code failure. This made him look for something that could help him know whether the code will work or not before it is committed to the repository. 

This curiosity led the way to the development of an automation server named Hudson. In 2011, there was an infamous dispute between the independent Hudson open source community and Oracle, which now has Sun Microsystems under its umbrella.

This dispute led to a fork, which was named Jenkins. Both Jenkins and Hudson continued to exist for a long time; however, Jenkins was the more preferred choice. The Hudson project was shut down in January 2020. Jenkins is still active.

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What is Jenkins?

Jenkins can be termed as an automation tool that is used by DevOps teams looking to bring continuous integration into their projects. It is open-source software that is built in Java. It is used through the lifecycle of software development.

Not just in development and testing, but in deployment as well. It allows developers to integrate changes much easily into their projects. Jenkins is also used for the continuous delivery of software projects. 

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How does continuous integration work?

Continuous integration (CI) is an integral part of the software development process. It can consist of a number of different tasks, including the use of unique functionality in the repository, feature development, and bug fixes amongst others.

A continuous integration tool, such as Jenkins, is great in identifying issues with current application sources and provides speedy response by checking the integration process with the help of automated build and test features. 

Continuous integration has come from a programming model that is associated with the Agile methodology. However, the concept can still be applied to all those programming models that are iterative in nature.

The waterfall models and other such development approaches can also benefit from what continuous integration has to offer. CI often works in tandem with continuous delivery (CD) to deliver executable code to production at a much faster pace and in an automated way. Listed below are common CI practices:

1. Regular code committing
2. Build staging
3. A build machine dedicated to the integration
4. Continuous feedback
5. Developer test categorization

Continuous integration can be released at whatever frequency you deem appropriate considering your project and company. So, companies that use CI have more regular releases than those that use traditional software development processes.

More and more companies have started using CI because of one simple fact – even the minutest of change in the code could give rise to a new build. CI can give continuous feedback during the development of software.

This helps DevOps teams to get rid of the errors in every stage of development. It also detects problems quite early in the development process. This makes these problems less disruptive, not too complex, and easy to handle. 

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How does continuous delivery work?

Continuous delivery is a part of the software development process that enables you to go ahead with development in such a manner that you are always ready to release the software to production. Here are a few times when continuous delivery proves additionally fruitful:

1. The DevOps team ensures that the software is deployment-ready even when feature development is under progress

2. The software is ready for deployment throughout the software development cycle

3. Deployment through push-button means is a reality for different versions of software to different on-demand environments

How can continuous delivery be achieved? The first requirement is that the software should be already undergoing continuous integration. The development team should then build the executables and perform tests on them to detect errors or bugs. Also, it is very important to test the executables in different production environments to ensure that the software is ready to be sent to production at any time. For this, having a deployment is necessary.

Automation of Jenkins allows companies to speed up their software development process quite significantly. Jenkins is capable of integrating different types of software development lifecycle processes, including building, testing, deployment, and others. Plugins are very important for ensuring continuous integration. If you are looking to add a new tool to Jenkins, you will first have to make sure that you install a plugin for it. 

Read: Jenkins Interview Questions & Answers

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What is Jenkins pipeline?

A Jenkins pipeline is a combination of jobs, tasks, or events that are connected to each other in a sequence. In other words, it is a group of plugins that enable continuous delivery pipelines to be easily integrated and implemented. Extendable automation works to support a pipeline in the creation of both complex and simple delivery pipelines in the form of code and with the help of domain-specific language or DSL.

Let us now discuss a little about continuous delivery pipelines and how they work. The basic characteristic of a Jenkins pipeline is that each event or task or job that it holds is dependent in one way or the other on one or more of these events, jobs, or tasks. Continuous delivery pipelines feature different states, such as build, test, deploy, release. All these states are connected to each other. 

A continuous delivery pipeline is a sequence that events of each of these states work in.  It is an automated expression that processes required for getting version control software. All the changes that are made to the software have to pass through several complex processes before the software is released. This process also ensures that the software is developed in a repeatable and reliable way and involves multiple testing and deployment stages, which the software progresses through. 

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JenkinsFile is a text file that is used to define Jenkins pipelines. JenkisFile is often used to implement pipelines in the form of code, and this entire process is defined using DSL. You can also use the JenkinsFile to write down the steps that need to be followed to run Jenkins pipelines. Mentioned below are some benefits of using JenkinsFile:

1. It makes reviewing the code on the pipeline easy.
2. It can help you execute pull requests for all the pipelines that you have created for different branches.
3. It is the one and the only source for your pipelines that can be modified by different users.
4. It can help you conduct an audit on your Jenkins pipeline.

JenkinsFile is defined using two types of syntax

Declarative pipelines syntax

Creating pipelines is much easier with this syntax. It features a well-established hierarchy that helps in creating pipelines. It offers you simple ways to exercise control over every aspect associated with the execution of pipelines. 

Scripted pipeline syntax

It uses a lightweight executor and runs on Jenkins master. It has its own set of resources that it puts to use to convert pipelines into atomic commands. As is quite evident from their definitions, both these syntax are quite different from each other. Not only this, but they are also even defined in different ways. 

Why should you use Jenkins pipeline?

Jenkins automates that software development process through its continuous integration capabilities. You can use different use cases to create a number of automation jobs and then use Jenkins pipeline to run all of them. Listed below are a few reasons for using Jenkins pipeline:

1. As it is implemented in the form of a code, Jenkins pipeline can have a number of users who can edit and execute the process. 
2. It supports projects that are larger in size than usual. Running multiple projects at a time or using pipelines in a loop are all possible. 
3. They are robust. You don’t have to worry if your server restarts under unforeseen circumstances. Jenkins pipeline would resume automatically. 
4. The pipeline process can be paused and not resumed until you receive user input. 

Jenkins Architecture

In this section, we will focus our discussion on how Jenkins helps both developers and testers? Let’s discuss the Jenkins continuous integration to understand that.

In the beginning, developers make all the changes that they want in the source code. This code is stored in the Git repository. Modification is followed y committing those changes. Jenkins server is doing its job and tracking changes made to the files stored in the repository. The changes made by the developers are detected by the Jenkins server. Jenkins then pulls these changes and begins working on a new built of the software based on those changes, 

The concerned team receives a notification if the build fails. On the other hand, if the build is successful, Jenkins deploys it on the test server. Developers are notified about build development and testing results. This cycle continues to repeat. 

Now that we understand how Jenkins works, it will be easier for us to make out the difference in its working and that of the ways that were used for releasing and deployment before it. 

So before Jenkins came to the fore, the process involved the building and testing of the complete source code. Locating and fixing errors and bugs were not at all easy tasks that used to delay the delivery of software. Developers had to wait a long time for test results. Deployment used to happen manually.

After Jenkins, all the changes in the source code are tested once they are made. Developers are not required to go through the complete source code for locating errors and bugs. The launch of build releases is much more frequent now. Developers are informed about the test results of all the changes and commits. Once you commit the changes, the Jenkins server can start executing other processes. 

Jenkins Distributed Architecture

Jenkins manages the builds with the help of master-slave architecture. Master and slave units communicate with each other using IP/TCP protocol. Here is a little download on how it all works.

Jenkins master

This is the primary server of Jenkins. It handles a number of tasks that include but are not limited to scheduling build jobs, recording and presenting build results, dispatching builds to slaves for execution, monitoring all the slaves offline as well as online, and others. Master Jenkins is capable of directly executing build jobs.

Jenkins slave

It runs on the remote server. The Jenkins server follows the requests of the Jenkins master and is compatible with all operating systems. Building jobs dispatched by the master are executed by the slave. The project can be suitably configured to choose a specific slave machine. 

Benefits of Jenkins

1. Jenkins is an open-source tool that is extremely easy to install and use. You need no extra components to use it

2. It is free and available to be used with different platforms, such as Windows, Linux, macOS, and others

3. It is widely used, so finding support on online communities is not a big problem

4. Jenkins automates all integration work. Integration issues are scarce, and so, it helps in saving time and money over the project lifecycle.

5. It is easy to configure, extend, and modify. It allows the instant generation of tests and building, automation, and deployment of code on different platforms

6. Jenkins can be configured to run CI and CD concepts properly

7. It can easily detect and fix issues. The software is always ready for a sudden release

8. Supports a variety of plugins, which allows better flexibility

9. It helps in detecting errors very early, thus saving developers a lot of time and hard work

Increase productivity with Jenkins plugins

Here are a few of the most common plugins used by developers.

1. Job generation plugin

Maintaining project jobs in growing or bigger organization is a little difficult, more so because developers are often working on different branches and releases. While you are ready to let developers create jobs on their own, you are not sure whether they will be able to meet company standards. This is a big dilemma. This plugin lets you define templates, which your developers can use to create jobs. You can disable configuration access of the template using the role-based authorization plugin. 

2. Global build stats plugin

Knowing your current capacity, capabilities, and usage is very important to prepare yourself for system requirements or capacity planning. You should be aware of the number of builds that are happening on a regular basis. You also need to know the time required to release builds. This plugin provides you with all the necessary information required to answer all these questions. 

3. GitLab/GitHub pull request builder

You can use this template to automate the code review process in GitLab/GitHub to a level that is higher than usual. For every pull request, you can expect this plugin to not only run the build but also build results and share the status with a pull request or collect important static analysis. This plugin tells a lot about the code that needs to be merged. It is also possible to define automatic merge in some circumstances using this plugin. 

Conclusion

This blog provides a sound idea of how Jenkins works and how it can be used for implementing different project ideas using CI/CD. It is one of the most preferred DevOps tools these days that makes things very easy with its effective interface and plugins.

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