If you want to use Con­tinu­ous In­teg­ra­tion (CI) in your team, you should use a simple but powerful CI tool. With Jenkins this kind of tool is at hand: The open source software offers an enormous number of pos­sib­il­it­ies, es­pe­cially through plug-ins, and for making the con­tinu­ous in­teg­ra­tion process more efficient.

Jenkins is based on Java and therefore runs on every platform. Since the software is shipped with Winston, a servlet mid­dle­ware, there is no need for ad­di­tion­al servers, such as Tomcat. In order for you to work suc­cess­fully with Jenkins, we will first explain how to install and configure the program. We will then show you an example of how to take the first steps in a project.

In­stall­a­tion of the software

Jenkins is available in many different versions. You can either choose a weekly version - Jenkins releases an update every week – or you can get the Long-Term-Support (LTS), in which a new version is released every three months. Under these two branches you have the choice between different releases. In addition to in­stall­a­tion packages for the usual operating systems (Windows, macOS, Ubuntu/Debian), a version for Docker and a web archive (.war) are also available.

Image: Overview of different installation versions of Jenkins
Jenkins has many different in­stall­a­tion files for you to choose from. Source: https://jenkins.io/download/
Note

In our example, we use the Windows Installer version 2.121.1 (LTS) under Windows 7. If you are using a different version or operating system, the setup process may be different. Since Jenkins is based on Java, you must have a current version of the Java tech­no­logy installed.

The Windows Installer will guide you through the in­stall­a­tion process. All you have to do is specify the desired in­stall­a­tion directory and start the in­stall­a­tion.

Jenkins setup

The in­stall­a­tion should only take a few seconds. Im­me­di­ately af­ter­wards, the program will open your preferred browser, and load localhost:8080. Then you’ll find the web interface to operate Jenkins. But first you have to take a step for security’s sake. Jenkins will have generated a random password for you. This can be found in the Jenkins directory, in the secrets folder, and in the ini­tial­Ad­min­Pass­word file. The file can be opened with any text editor. Copy the string, and paste it into the field in the web interface.

Image: Prompt to unlock the Jenkins installation
Before you can start Jenkins, the ap­plic­a­tion prompts you to enter a generated code.
Image: Example of an admin code for Jenkins
You can open the password file with any editor

Now it's time to get going. The setup wizard will ask you if you want to choose which plug-ins to install, or if you prefer to use a default setting that has all the important ex­ten­sions already in­teg­rated. If you're new to Jenkins, this option should be fine. And don't worry - ad­di­tion­al plug-ins can be installed at any time, easily and without any issues.

Image: Installation of default plug-ins in Jenkins
The most important ex­ten­sions are already included in the standard selection of plug-ins

Then create a first user. If you are working on your project alone, you can skip this step and simply use Jenkins as admin - in the Jenkins settings, you can still create new users with different rights later. In the final setup step, you still have the pos­sib­il­ity to enter a Jenkins URL. The cor­res­pond­ing field has already been entered in localhost:8080. If you have installed Jenkins on a server (which should be the case in a pro­fes­sion­al work en­vir­on­ment), enter the correct path to the Jenkins directory here. Save your entries and complete the setup.

Tip

Further settings can also be made later in the Jenkins con­fig­ur­a­tion menu.

Jenkins - in­tro­duc­tion to the way it works

You may find that starting a project gives you the best insight into how Jenkins works. Here is our step-by-step tutorial for creating a project in Jenkins. You start Jenkins with a com­pletely empty working en­vir­on­ment. To start a new CI project, you must create a new job. This is done via the prominent notice in the middle of the window ("create new jobs") or via the menu item "new item" on the left side.

Image: Jenkins web interface
When you start working with Jenkins, you must first create a new job.

The next step is to give your project a name, and select what you want to achieve:

  • Freestyle project: Jenkins connects a version control system to a build system.
  • Pipeline: This creates a pipeline across multiple build agents.
  • Multi-con­fig­ur­a­tion project: If you have a project that requires different settings, for example, because you use different test en­vir­on­ments, select this option.
  • Folder: A folder is a container in which you can store nested objects.
  • GitHub Or­gan­isa­tion: This option searches all re­pos­it­or­ies of an account for GitHub.
  • Mult­ibranch Pipeline: This allows you to create several pipelines directly.

Jenkins focuses on  freestyle projects, which is why we will create one in our example.

Image: Setting options for a project in Jenkins
When you create a job in Jenkins, detailed settings are available to you.

On the following page you have numerous setting options. You configure your project in six cat­egor­ies. Suppose you write a program in Java and want to use Con­tinu­ous In­teg­ra­tion. First, we will deal with source code man­age­ment. The sample program is located in a Git re­pos­it­ory on your computer (it is also possible to connect Jenkins to GitHub, for example). Therefore, enter the correct directory under the item "Git". You can also work with a Sub­ver­sion.

The next step is to select the build trigger. This de­term­ines the situ­ations in which Jenkins should start a build. This is possible, for example, by a special script of another program after another build has been completed, or regularly at certain time intervals. You can also trigger a build manually when you are ready - as we will do in our example.

The build en­vir­on­ment that Jenkins lets you configure next contains more options around builds: Should it be aborted, for example, if the process hangs? Or do you want to print a timestamp in the console? None of the options are mandatory.

After all, it's all about the build: Here you determine what your program should be built with. Since you have already in­teg­rated con­nec­tions to Ant and Gradle in the standard selection of plug-ins, you can choose one of these programs. However, it is also possible to use simple command line commands. Select the option for batch commands and let your program compile:

javac MyProgram.java
java MyProgram
Image: Setting options for a project in Jenkins
During the build, you can establish a direct con­nec­tion to another tool or use command line commands.

After that, Jenkins gives you the ability to perform actions after the build. Testing is an important factor here. Use the "Publish JUnit test result report" option to connect Jenkins and JUnit to integrate results from the Java test framework. With ad­di­tion­al plug-ins you can also connect Jenkins to other test en­vir­on­ments. You can even run automatic tests using Jenkins. Emailing yourself and others about the status of the build is also an option. The final step is simple: save the in­form­a­tion and you have created your first job.

Tip

If you want to install plug-ins, you should restart the Jenkins server. You can do this by logging out and adding safeRe­start to the URL in the address bar of the browser (e.g. localhost:8080/safeRe­start). If you now log in again, you can confirm that you want to restart.

Each project has its own subpage in Jenkins. Here you can trigger a build, change the settings again and see the status. On the “status” page, Jenkins also shows you the build history. Was the last build suc­cess­ful or not? Blue dots show that it was suc­cess­ful, red dots mark an error – and you should fix this straight away. At this point, you can also see when a build is being created. A click on the build number takes you to a detail page where you can also view the console output.

Image: Status page of a project in Jenkins
In the build history you can see at a glance which builds worked and which didn't.

The Jenkins Dashboard shows you all the projects you're working on. Here, too, the program high­lights the status of the project in colour. You will also receive in­form­a­tion about the build stability in the form of a weather report. This is a statistic how stable the builds of the project are on average. If more than 80 percent of your builds are suc­cess­ful, you will see a sun. Below this value, the symbolic weather gets worse and worse.

Image: Dashboard by Jenkins
The dashboard shows the status of all projects.
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Note

Jenkins gives you many more ways to customise the program to your working con­di­tions and simplify your con­tinu­ous in­teg­ra­tion process. You will find a suitable solution for most situ­ations, in par­tic­u­lar if you use the various plug-ins.

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