30+ Best Jenkins Interview Questions For Engineers

jenkins interview questions

We've compiled the absolute best Jenkins interview questions and answers for your upcoming job interview in the product management or engineering department. Continuous Integration is by far the most important aspect of DevOps for integrating different DevOps stages. Out of all Continuous Integration tools, Jenkins is the most common and most famous tool around. Unfortunately, many software and tech startups sorely underutilize Jenkins pros and often don’t ask interview questions that involve this tool.

We put together a guide to some vital Jenkins Interview questions and answers that hiring managers can use to find the best Jenkins developers for hire. First, let’s explore exactly what Jenkins is and why it is so important to consider when hiring coding specialists.

What is Jenkins?

Jenkins is an open source automation tool that is written with Java, complete with plugins built for Continuous Integration usage. Jenkins is designed to build and test out various software projects continuously, making it easier for developers to integrate changes and adjustments to the project. Jenkins also makes it easier for users to acquire fresh builds and to continuously deliver software by integrating it with a substantial number of testing and deployment technologies.

With Jenkins, businesses can accelerate software development by way of automation. Jenkins integrates development life cycle processes of various types, including document, build, test, package, stage, static analysis, deploy, and many other types.

Jenkins manages Continuous Integration with the assistance of plugins. Plugins allow the integration of different DevOps stages. If one wishes to integrate a particular tool, they will need to install the appropriate plugins for that tool.

Why is Jenkins Covered in Technical Interviews?

Jenkins should be covered in technical interviews because as a tool, it’s extremely useful. Some of the benefits of Jenkins include:

Ideally, small tech startups can utilize the “free” factor of Jenkins in lieu of more expensive and ineffective tools for DevOps. It’s definitely worth throwing in some Jenkins interview questions when hiring developers for your business’ development and operations.

Jenkins Interview Questions and Answers

1. In your own words, describe what Jenkins is.

Look for the basic definition in their answer, which should sound something like this: Jenkins is an open source automation tool written with Java and has plugins built for Continuous Integration purpose. Jenkins is built to build and deploy software projects continuously, making it substantially easier for developers to integrate new changes to the project, and also making it easier for users to obtain a fresh build. It also allows one to continuously deliver their software by integrating with a large number of testing and deployment technologies. The goal here is to really make sure that the interviewee not only knows what Jenkins is, but is familiar with its inner workings.

2. Can you offer an example of a Jenkins use case?

The answers to this question will vary among different interviewees, but the following is an example of a Jenkins use case: First, a developer must commit the code to the source code repository. At the same time, the Jenkins server will check the repository at regular intervals for new changes. Not long after a commit occurs, the Jenkins server will detect the new changes that have occurred in the source code repository. Jenkins will then pull those changes and will begin preparing a new build. If the build fails for whatever reason, then the appropriate development team will be notified. If the build is successful, then Jenkins will deploy the build to the test server. After sufficient testing, Jenkins generates feedback and then will notify the appropriate developers about the build and test results. Jenkins will continue to check the source code repository for new changes made in the source code and the entire process will continue to repeat throughout the project.

The goal here is to get the interviewee to not only define what Jenkins is but also to describe why Jenkins is used in lieu of other Continuous Integration tools.

3. What are some of the benefits of using Jenkins in a software project?

There are many benefits when it comes to using the Jenkins tool. At the integration stage, build failures are cached for reference. For each and every change within the source code, an automatic build report notification is generated that makes for optimum tracking and testing. In order to notify the appropriate developers about the build report successes or failures, it is integrated into a Lightweight Directory Access Protocol (LDAP) mail server. Jenkins also allows for continuous integration of agile development and testing-friendly development. It can also make the tracking of bugs at the early stages in the development environment quite easy, rather than letting bugs through into the production stages. It’s worth noting that seasoned Jenkins users may list more benefits in addition to the above benefits.

4. Name the requirements for using the Jenkins tool.

The pre-requisites of Jenkins include a source code repository that is accessible, and a working build script checked into the build repository.

5. Many as many user-friendly plugins for Jenkins as you can.

There are thousands of useful plugins one can use for the Jenkins tool. A handful of the really important ones include Maven 2 project, Jenkins Maven, Jenkins subversion, Git, Amazon EC2, HTML publisher, Copy artifact, Join, Green Balls, Dashboard view, View job filters, Gatling, BlazeMeter, Bootstrapped multi-test result report, Categorized view, Build monitor, Blue Ocean, Simple theme, Folders, Monitoring, Metrics, Performance, Performance publisher, Kubernetes, Self-organizing swarm modules, Azure container service, Job generator, Github and Gitlab pull request builder, JIRA, SCM sync configuration, Test results analyzer, Job DSL, Build pipeline, Multijob, SCM API, and GitHub integration. Note that the interviewee may list even more than the above useful plugins. A Jenkins developer who is familiar with many plugins can be a useful addition to a development team.

6. List the commands one can use to manually launch Jenkins.

To begin, a user will need to open the console or command line, then to the Jenkins installation directory. From there, three codes can be used: jenkins.exe start to launch, jenkins.exe stop to stop Jenkins, and jenkins.exe restart to reboot the tool.

7. How would you go about setting up a new Jenkins job?

To begin, a developer would go to the top Jenkins page and select “new job” from the menu. Then they would select “build a free-style software project.” There are several different elements one can select for a job. You can choose optional Source Control Management (SCM) which can include a Concurrent Versions System (CVS) or Subversion wherever one’s source code occupies. You can select optional triggers to control when Jenkins will execute builds. You can also select any type of build script that can perform the build, such as batch file, ant, maven, shell script, etc. You can also choose optional steps to collect data out of the build, such as archiving the existing artifacts or recording JavaDoc and then testing the results. Lastly, you can notify other developers or systems within the build result, via sending emails, instant messages, updating the issue tracker, etc.

8. Describe how you would copy files and create backups within Jenkins.

This is a pretty direct and simple solution. All one needs to do to create a reliable backup in Jenkins is to schedule consistent and regular JENKINS_HOME directory backups. This directory houses all of the build job configurations, the build history, and the slave node configurations. In order to create a sufficient backup of your unique Jenkins setup, simply copy the JENKINS_HOME directory. If you want to copy a job directory, that is possible as well.

9. How does one go about securing Jenkins?

This is a fairly direct step-by-step process. First, make sure global security is activated. Make sure that Jenkins is properly integrated with your business’ or team’s user directory with the appropriate plugin. Verify that matrix or Project matrix is enabled to fine tune access. Automate the processes of setting rights or allowing privileges in Jenkins with a custom version controlled script. Make sure to limit physical access to Jenkins data and/or folders. Every once in a while, run security audits. This is all it really takes to secure Jenkins.

10. Describe step-by-step how to deploy a custom build of a new plugin.

Stop Jenkins using the appropriate command, copy the customized HPI to $Jenkins_Home/plugins, remove the previously expanded plugin directory, create a new empty file called plugin.hpi.pinned, then finally oot Jenkins with the appropriate command.

11. What are the two components that Jenkins is largely integrated with?

Version Control systems such as GIT or SVN, and build tools such as Apache Maven are the two main components of Jenkins. Note that it is very important for the interviewee to mention these two components, but there are other components that Jenkins can use as well that interviewees may mention.

12. List the SCM tools that Jenkins supports.

There are a handful of tools that Jenkins can support and utilize. These include AccuRev, CVS, Subversion, Git, Mercurial, Perforce, Clearcase, and RTC.

13. Describe the difference between Maven/Ant and Jenkins.

This is simple. Jenkins is a Continuous Integration tool, while Ant and Maven are individual build technologies.

14. Name the four ways that one can schedule a build in Jenkins.

You can schedule a build via Jenkins in four different ways: Via source code management commitments, after completing other available builds, by running the build at a specific time (through crons), and with manual build requests.

15. Describe the process of moving and/or duplicated Jenkins from one server to another server.

I would take on this cask by duplicating the jobs directory from the original server to the new server. These are several ways I can go about doing that. One way includes moving a job from one installed version of Jenkins to another installed version of Jenkins by just copying the corresponding job directory. Another way to move or duplicate Jenkins between servers is to make a copy of an existing job via creating a clone of a job directory by a different name. The last way you can move Jenkins between servers is to rename an existing job through renaming a directory. It’s important to remember that if you change a job name, you will need to change every single other job that tries to call or connect with the renamed job.

16. What does a developer do when they find a broken build for their project in Jenkins?

A developer would, first of all, find that broken build quickly. They would then open up the console output for the broken build in question and attempt to see if any file changes were missed. If they are unable to find the problem that way, then they should clean and update their local workspace to duplicate the problem on their local system in order to try to solve it. After testing, the broken build should at least be diagnosed or fixed. Note that there are actually a few ways to go about fixing a broken build for a project in Jenkins, but the above answer is the most common way of doing so.

17. Is there a relation between Jenkins and Hudson?

Yes. Hudson was actually the original version and namesake of the current version of Jenkins.

18. What are the Jenkins installation requirements?

There are several requirements for installing Jenkins. Jenkins requires Java 7 or above as well as Servlet 3.1 to function properly. Java 8 is often recommended for the current version of Jenkins. Jenkins also requires a pretty hefty amount of memory to operate well. For smaller installations, starting around 256MB to 1GB is usually sufficient.

19. What is the average cost of Jenkins?

Jenkins is 100% free to use, as are the custom plugins created by the developer community.

20. How can one close a Git repository with Jenkins?

If you want to clone a Git repository through Jenkins, you will have to enter the administrative email and user name for your Jenkins system. Switch into your job directory and execute the git config command in order to do so.

21. What can one do to make sure that a project build doesn’t break down or fail within Jenkins?

I would personally make sure that I had performed a successful clean install of Jenkins on my local machine with all the necessary tests. Then, I would make sure that I had checked in with all code changes. Then, I would do something called a “synchronize” with the repository in order to make sure that all of the required configuration data, Project Object Model (POM) changes, and any additional differences are checked into the repository.

22. What are some differences between Jenkins and their competitor tool TeamCity?

TeamCity is not open source and allows for default security and individual validation. It is not as widely used as Jenkins. Jenkins is open source but does not have default security and individual validation. It is much more widely used than other Continuous Integration tools.

23. How can one configure and use third-party tools within Jenkins?

There are only a few steps to doing this. First, I would have to first install the third-party software in question. Then, I would need to have on hand the plug-in that supports the third-party tool. After, I would need to configure the third-party tool in the admin console. Once these steps are taken, I can then use the plug-in from the Jenkins build job.

24. What are two ways a Jenkins node agent could be configured to communicate with the Jenkins master?

From the browser window, I would launch a Jenkins node agent. Another way to configure a node agent would be from the command line, where I would launch a Jenkins node agent. When one activates a Jenkins node agent, it will automatically download a Java Web Start (JNLP) file. A new process is then launched on the client machine through the JNLP when it activates and runs.

25. What are the necessary steps included in a Jenkins pipeline?

A wholly complete Jenkins pipeline will always include building a project through the source code, sending it through a variety of units, integrating it, testing it for user acceptance and performance, and then lastly deploying the package application on the appropriate application server. To shorten this answer, the steps in the Jenkins complete pipeline are build, test, and deploy.

26. Is there are a way to turn Jenkins security off in the event that the administrative users have accidentally locked out of the admin console?

There is a specific folder in the Jenkins directory that contains one specific file called config.xml. In order to disable Jenkins security, you will need to find the security code in that file and set it to “false.” Reboot Jenkins and your security should be disabled and your admin should be able to access the project.

27. What is the official programming language used to build Jenkins?

Jenkins is written only in Java. The current recommended Java version for use with Jenkins is Java 8.

28. Describe in great detail what Continuous Integration is and how it relates to Jenkins.

Continuous Integration is simply a process in which all coding and development work is integrated as early as possible into any project. The resulting artifacts are automatically created and tested. This process allows developers to identify errors as early as possible. Continuous Integration is a reliable way to set up automation in a project before any issues can slip their way through into production, so it is becoming a more popular method of coding integration nowadays. Jenkins is a widely used open source tool used to perform continuous integration and build automation. Basically, Jenkins just facilitates Continuous Integration. The main functionality and benefit of Jenkins is to execute a prewritten list of steps or to compile Java source code, and build a Java Archive (JAR) from the subsequent classes. The trigger for this execution can be a time or an event-based command.

29. What are some CI steps that Jenkins can execute?

You can perform a software build using a specific build system like Apache Maven or possibly Gradle. You can execute a shell script or archive a build result. You can engage in running software tests as well. Note that there are other, less common answers to this question that will work as well.

Jenkins offers a Debian and Ubuntu package which install and register Jenkins as a start service. Linux will create a script (/etc/init.d/jenkins) that will start Jenkins automatically after booting. Jenkins will store all of its settings, build artifacts, and logs in its respective home directory. The default Ubuntu directory for Jenkins is /var/lib/jenkins.

31. How can one create a new user with Jenkins?

Boot Jenkins. Access “Manage Jenkins.” Then go to “Manage and Assign Roles.” Then go to “Assign Roles” to grant a new user additional rights for access to your project. They will need a username, password, full name, and email address. Then, navigate over the “Manage Roles” to properly define access restrictions for that user in detail. You can then check off whether or not that user can read, delete, configure, discover, build, work on, cancel, or view the status of a build job that starts with the C-MASTER or M-MASTER prefixes.

How was our guide to interview questions and answers for Jenkins? Do you feel a bit more confident in finding the best Jenkins developers for your project or business? Tell us what you think in the comments below.

author: patrick algrim
About the author

Patrick Algrim is an experienced executive who has spent a number of years in Silicon Valley hiring and coaching some of the world’s most valuable technology teams. Patrick has been a source for Human Resources and career related insights for Forbes, Glassdoor, Entrepreneur, Recruiter.com, SparkHire, and many more.


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