What is Jenkins? A Guide to Continuous Integration with Jenkins

If you have been introduced to the term Jenkins and are unsure how it relates to application development, you are at the right place. Jenkins is an open-source tool that helps the DevOps team in continuous integration. Now, what exactly is continuous integration? It is a process where there is continuous testing of source code after it is committed to making sure that it is free from bugs or errors.  

Prior to deploying the code to production, it is crucial to test it for problems. This is especially important when a new build of a particular software product is produced. If the build is error-free, it is ready to go to production. Otherwise, bugs have to be fixed. Continuous Integration helps developers find bugs or errors in software builds at early stages, which, in turn, reduces the cost of fixing them at later phases.  

With a plethora of continuous integration tools available out there, Jenkins is among the top-ranked ones. Jenkins is an open-source automation tool developed in Java primarily for continuous integration. With Jenkins, developers find it easy and straightforward to integrate any change into software products. If you wish to learn Jenkins in detail, we recommend you enroll in our Jenkins Training. Here we have prepared a complete guide on Jenkins to explain what Jenkins is and how it works to achieve continuous integration.  

What is Jenkins?

Continuous integration is one of the most important terms used in DevOps when it comes to integrating different DevOps stages. Jenkins is the most popular and widespread tool that DevOps teams use to create software projects by developing and testing them continuously. It offers the most needed automation to accelerate the development process.  

With Jenkins being a server-based application, you need a web server, like Apache Tomcat, to make the application operable. By integrating a large number of testing and deployment technologies, Jenkins lets you deliver your software products continuously. It is capable of combining the various phases of the development life cycle, such as build, test, package, deploy, analysis, and many others. 

History

Jenkins is a fork of Oracle's patented Hudson project. But later, it was made open source and CD foundation, a Linux-affiliated organization that takes care of Jenkins.  

Since its inception, continuous integration has seen significant changes. A daily build was the norm initially, but that has changed. Each team member submits work (called a commit), and a build is done for each major change. There are several advantages to using continuous integration, such as ongoing feedback on the software's progress. Jenkins comes in handy.  

Jenkins for CI/CD

Along with continuous integration, Jenkins also supports continuous delivery and continuous deployment. Let us discuss all three terms in detail.  

Integrating all of the code changes made by several developers into a single project is known as "continuous integration." After a commit, a piece of code is put through a series of tests to ensure it is free of errors and bugs.  

There's a good probability that one of the many commits made by the development team will include a bug. It's much simpler to catch these issues early on using CI than in the old days of manual testing. A build is a process through which all the source code is combined into a single executable. If this build is green, the tested and executed code is ready for deployment. If the problem persists, the team will have to start over and fix it. The word "continuous integration" or "continuous deployment" refers to the fact that this is an ongoing operation.  

When used as a continuous integration tool, Jenkins aids software development teams in quickly locating and fixing bugs as well as automating the integration of new code as it is developed.  

Continuous development refers to the process of automating the development and packaging of source code and deploying it to testing and production environments. Continuous deployment is the process of automating the deployment of the source code to its desired destination.

When you leverage Jenkins for CI/CD, automation ensures that there is less number of errors in source code as Jenkins is specially programmed with the best practices and procedures to do so. Jenkins specifies the desired state, and the automation server performs everything to maintain that state. 

Additionally, you can increase the release velocity of software builds because deployments in Jenkins are not dependent on any personnel, such as operator availability. Hence, the development and operations teams can reduce the stress of constantly integrating and deploying changes with Jenkins.  

Jenkins and Microservices

Microservices is an architectural approach to software development. It composes a software application as a group of multiple loosely-coupled services. This type of approach is useful when you need to develop complex and extremely large software applications. It ensures rapid and frequent delivery of applications. Also, the microservices architecture makes it possible to quickly add new features to existing applications and bring them to market.  

When it comes to a microservices architecture, Jenkins becomes necessary. As the primary objective of microservices architecture is to update existing features or add new features continuously, Jenkins comes in handy as it automates various development and deployment tasks. So when you incorporate Jenkins into your suite of development tools, you will find it easier to develop applications that leverage the microservices architecture.

Jenkins Automation

Jenkins offers various plugins to automate various development activities. It provides approximately 1,600 plugins that are spread across five different categories, namely platforms, UI, administration, source code management, and build management.  

Jenkins is not simply limited to continuous integration and continuous delivery (CI/CD). It is among the processes that you can automate using Jenkins. As it is an automation server, you can automate every sort of development task through an extensive set of plugins.  

How Does Jenkins Work?

Jenkins can operate on Windows, macOS, many Unix distributions, and Linux. You can use the Oracle JRE or OpenJDK if you have a Java 8 virtual machine. A Jetty application server often hosts Jenkins as a Java servlet. Not only that, but you can also use the Apache Tomcat Java application server. In recent years, Jenkins has been able to operate in a Docker container. However, there are read-only Jenkins images found in the Docker Hub repository.  

Let us now understand how Jenkins works. 

Initially, a developer integrates a new piece of code into the existing source code and commits. Now, the Jenkins server performs a regular repository check and finds and pulls the changes as soon as the developer commits the new code. In addition, it plans for a new build.  

Next comes the testing of the new build. Jenkins carries out testing on the new build and alerts the developer if it fails. Before moving the build into the production pipeline, Jenkins prepares an environment for the deployment of the build suitable for User Acceptance Testing (UAT), where real users can use and test the build.  

This process gets repeated endlessly through the whole development cycle.  

In Jenkins, it's simple to identify which commit was responsible for the build failing. The build process will proceed to the next stage if all unit tests pass. Also, the tool uses many servers to execute parallel builds to reduce the time it takes to accomplish other tasks.  

Google and Amazon, among others, are the firms that have accomplished continuous delivery. So they may make many deployments to production throughout the day.  

As an immensely capable tool, Jenkins' continuous integration pipeline uses several technologies for various tasks, including host- and monitor-side code testing and compilation.  

Jenkins Plugins

Plugins work as extensions in Jenkins. You can use both the web interface and the command line to load and unload plugins. Using these services, you may enhance Jenkins' functionality and make it work with other programs. The Jenkins community already has more than 1600 plugins available for usage in a variety of scenarios.  

With plugins, you can:  

• Integrate a variety of developer tools into the Jenkins environment.  
• Manage the administration of Jenkins.  
• Improve Jenkins for code and build management.  
• Add new UI components to Jenkins Web UI.  
• Communicate with operating systems through FTP, CIFS, and SSH 

These are some of the basic tasks. You can do a lot more using Jenkins plugins.  

One of the most typical applications of plugins is to offer integration points for CI/CD sources and destinations. These sources and destinations include SVCs, like Git and Atlassian BitBucket, container runtime systems like Docker, virtual machine hypervisors like VMware vSphere, public cloud instances like Amazon AWS, and private cloud systems like OpenStack.  

Jenkins plugins are developed in Java. Design patterns and Java Annotations for plugins are used to specify how the plugin is created, how it extends other plugins, and how its user interface appears in Jenkins. You may also consider enrolling for DevOps Online Training to upscale yourself. 

Jenkins Pipelines

A pipeline is a set of actions that Jenkins will take to complete the CI/CD tasks. In other words, we can say that a Jenkins pipeline is a collection of interconnected tasks that need to be accomplished in a particular order. Pipelines are necessary for the operation of Jenkins. These are kept in a Jenkinsfile as plain text. JSON-like curly bracket syntax is used in the Jenkinsfile.  

Curly brackets enclose each step in the pipeline, expressed as a command with arguments. For the code to move through the Jenkins pipeline, it must first be committed to the source code repository. If you prefer writing code, you may construct a Jenkinsfile using a graphical user interface (GUI).  

Types of Jenkins Pipelines

Scripted and declarative are the two types of Jenkins pipelines. When a DevOps engineer writes a Jenkins pipeline, they choose either to create in the scripted syntax or the declarative one.  

At the time when Jenkins was introduced, scripted pipelines were only available. However, developers widely adopted this type of Jenkins pipeline because of two reasons, as follows:  

• Scripted pipelines provide a domain-specific language that simplifies a lot of developer tasks.  
• They support the injection of Groovy code anytime. Groovy is a programming language based on the Java Virtual Machine.  

However, when using Groovy code inside Jenkins pipelines, it violated the fundamental principles of Jenkins, i.e., Jenkins pipelines should be easy to read, easy to manage, and simple. This resulted in declarative Jenkins pipelines.  

Declarative Jenkins pipelines do not support the injection of Groovy code. If injected, it results in a compilation error. On the flip side, it supports conditional statements that provide support for error handling, adding logging, and accessing environmental variables.  

Scripted and declarative pipelines are different only in terms of the programmatic approach. While declarative pipelines use a declarative programming model, scripted ones leverage the imperative programming model. It is important to note that both these types of pipelines run on the Jenkins subsystem. There is no difference in the performance and problem solvability perspective.

Scripted Pipeline vs Declarative Pipeline: Syntax Difference

Let us know see how the syntax of Scripted and declarative pipelines differ.  

Scripted Pipeline 

pipeline {  
agent any 
stages { 
stage(‘Build) { 
steps { 
} 
} 
stage(‘Test’) { 
steps { 
} 
} 
stage(Deploy) { 
steps { 
} 
} 
} 
} 

Declarative Pipeline 

node { 
stage(‘Build’) { 
} 
  stage(‘Test’) { 
} 
stage(‘Deploy’) { 
} 
} 

Jenkins Security

The servers and the users are the focus of Jenkins security. The server, whether a virtual machine (VM) or bare metal server, is set up to interact with the minimum number of processes possible. This is possible with a typical server OS and network security mechanism. And it is possible to protect any other server in the same way.

A small number of users are allowed access to the server by employing common approaches such as multifactor authentication, such as the Jenkins UI. The user security features of the HTTP server that is used for the UI can be used to perform this task.

Security measures likewise protect the internal user database of Jenkins. The Jenkins Web UI is where you'll find these measures. Jenkins also supports the Security Realm and the Authorization Realm. The Security Realm controls a user's access to Jenkins, while the Authorization Realm controls their permissions.

Blue Ocean, the Jenkins GUI

Reinventing the user experience of Jenkins, Blue Ocean aims to model and display the software delivery process by exposing information vital to development teams using as few clicks as feasible while strictly adhering to the extensibility at the center of Jenkins. Blue Ocean is still at the alpha stage of development, but the goal is for Jenkins users to be able to install it alongside the Jenkins Classic UI through a plugin.

Blue Ocean's user interface strives to simplify the user's journey by removing extraneous elements and simplifying the menu structure. In addition, the modern visual design provides much-needed relaxation for developers, as displays adapt instantaneously to server changes making laborious page refreshes a thing of the past. Not only that, but it also provides pipeline visualizations with an integrated failure detection function.

Jenkins Docker

The Docker image for Jenkins is also available. To use Jenkins through a Docker image, you must select the SCM type in the first step. Then provide the URL and the required credentials to create a pipeline from one repository or scan all company repositories. For every Jenkinsfile, there is a pipeline.

You can check the following Blue Ocean Docker image for reference:

As you run some pipelines, the plug-in will show their status as available in the image:  

You can also zoom in and check the steps involved in each pipeline:

Why Use Jenkins?

Like all software programs, Jenkins also has its advantages and disadvantages. Here in this section, we will discuss the specific advantages and disadvantages of using Jenkins,  

Advantages

• Installing Jenkins is simple. It requires no further tools or installations.  
• Jenkins works seamlessly across all operating systems. You can run it on Linux, Windows, OS X, etc.  
• Jenkins configuration is simple. It's modifiable and expandable. Code deployment and test report generation are fast. Jenkins may be configured for CI/CD.  
• It's plugin-rich. Jenkins' large library of plugins makes it adaptable and allows creating, deploying, and automating across platforms.  
• Jenkins provides amazing help. As the most popular open-source server, it's free. Also, agile teams fulfill your inquiries globally.  
• Jenkins ensures automated integration work where integration issues are minimized. This helps projects save money and time.  
• With Jenkins, developers can find coding issues quickly. This prevents large-scale integration errors.  

Disadvantages

• Jenkins management is difficult. There is a need for a server administrator to monitor all of its actions.  
• While being compared to contemporary UI trends, users may find that Jenkins lacks user-friendliness.  
• Often continuous integration pipelines fail upon changing the settings. Therefore, the developer must restart the integration after any change in Settings.

Conclusion

This brings us to the end of the discussion on Jenkins. Being an open-source automation tool, Jenkins significantly reduces the stress of developers in continuously integrating new features into a software product and deploying them into the production environment. However, it is important to remember that Jenkins simply automates development tasks and does not eliminate the need to write code or script for every development step. For more information on Jenkins, check KnowledgeHut’s Jenkins Training.