Jenkins is an open-source automation server that provides hundreds of plugins to support building, testing, and deploying any project. It provides more than 1700 plugins that can automate virtually anything. It enables humans to focus on doing things that machines cannot.
We can commonly use Jenkins for building projects, running tests to identify bugs and other issues, static code analysis, and deployment. It automates various activities associated with software development, such as building, testing, deploying, and continuous integration and continuous delivery.
Since Jenkins is a server-based application, it requires a web server, such as Apache Tomcat, to run on various systems, such as Windows, Linux, and macOS.
Kohsuke Kawaguchi, a Java developer at Sun Microsystems, created an automation server in 2004 called Hudson. This server automated build and test tasks during the software development process.
When Oracle owned Sun Microsystems, they forked Husdon and named it Jenkins in 2011. Many organizations and companies leverage Jenkins since it helps software developers to deliver fully-functional software much faster to end-users. Since it is employed by many organizations, learning Jenkins can be a great idea.
If you are a beginner and planning to appear for the Jenkins interview, this article is a perfect guide. It intends to walk you through some of the most commonly asked Jenkins interview questions. So, let us get started!
Top Jenkins Interview Questions and Answers
Here is a compiled list of the most frequently asked Jenkins interview questions and their answers to help you crack your next interview. We have divided Jenkins interview questions into three different levels, namely beginner, intermediate, and advanced.
Beginner-Level Jenkins Interview Questions
1. What do you know about Jenkins?
Jenkins is an open-source automation server that automates the processes involved in the software development life cycle ( SDLC ). Also, it facilitates continuous integration and continuous delivery. With Jenkins, software developers can build and test their software projects continuously. In short, Jenkins automates and accelerates the software development process.
2. Explain the features of Jenkins.
The following are the salient features of Jenkins:
- Easy Installation: Jenkins is a self-contained Java-based automation server that comes with ready-to-run packages for Windows, Linux, macOS, and Unix-like systems.
- Easy Configuration: Jenkins is easy to set up and configure through its web interface that comes with built-in help and on-the-fly error checks.
- Available Plugins: Jenkins can integrate with almost every tool in the continuous integration and continuous delivery toolchain with the help of plugins available in the Update Centre.
- Extensible: It is possible to extend Jenkins through its plugins architecture.
- Easy Distribution: Jenkins can distribute work across multiple machines, i.e., it distributes building, testing, and deploying software projects across multiple machines.
- Continuous Integration and Continuous Delivery: Since Jenkins is an extensible server, we can use Jenkins as a Continuous Integration server or we can turn it into the continuous delivery hub for any project.
3. What are the advantages and disadvantages of Jenkins?
The following are the advantages of Jenkins:
- Jenkins is one of the most widely used and most preferred CI/CD tools, and it is free-to-use and open-source.
- We can enhance the functionalities of the Jenkins environment with the help of plugins. Through these plugins, we can make Jenkins suitable to meet the specific needs of organizations.
- Jenkins can integrate with major cloud platforms, including Google Cloud, Amazon EC2, and Digital Ocean.
- Software developers can easily track and identify bugs in software projects through Jenkins.
- Jenkins can execute bash scripts, shell scripts, ANT, and Maven targets.
The following are the disadvantages of Jenkins:
- The interface of Jenkins is outdated and not user-friendly.
- Jenkins is not easy to maintain. Since it runs on a server, the server administrator skills are a must to regulate its activities.
4. Enlist some useful plugins in Jenkins.
The following are the most popular and useful plugins in Jenkins:
- Maven 2 Project
- HTML Publisher
- Copy Artifact
- Green Balls
- Amazon EC2
- As soon as the commit occurs, the Jenk
- Slack Notification
5. What are the system requirements for installing Jenkins on Windows?
To install Jenkins on Windows system, there are a few hardware and software prerequisites:
- A computer or laptop with at least 256 MB of RAM.
- 1 GB of free space on the hard disk.
We need the recent update of either Java Development Kit (JDK) or Java Runtime Environment (JRE) since Jenkins is a Java-based automation server.
6. How can we achieve continuous integration in Jenkins?
We can achieve continuous integration in Jenkins with the following steps:
- Firstly, developers commit the source code changes to the shared Git repository.
- Meanwhile, Jenkins checks the shared Git repository at regular time intervals.
- The Jenkins server detects changes that occurred in the shared repository, and then it will pull those changes and start developing a new build.
- In case the build fails, the Jenkins server reports to the concerned team.
- If the build is successful, the Jenkins server deploys it in the test server.
- After finishing the testing, Jenkins generates feedback and reports to developers about the test results and the build.
- This entire process keeps repeating.
This is how we can achieve continuous integration in Jenkins.
7. Explain the term Continuous Integration. and Continuous Deployment.
Continuous Integration (CI) is a DevOps software development practice of regularly merging or integrating code changes from multiple contributors into a shared repository, after which automated builds and tests are run. The primary objective of continuous integration is to detect bugs quickly in a software application, enhance software quality, and minimize the time required to validate and release new software updates.
8. Explain the term Continuous Delivery.
Continuous Delivery (CD) is a software development discipline where software development teams produce software applications in short cycles. Alternatively, we can define continuous delivery as a software development practice where we build software so that we can release software at any time.
9. Explain the term Continuous Deployment.
Continuous Deployment is a software release process where software developers deliver new software functionalities frequently through automated deployments. In other words, continuous deployment is a software engineering approach that uses automated testing to make sure that the changes made to a software application are correct and stable for immediate deployment of that application to a production environment.
10. What do you know about the CI/CD pipeline?
The CI/CD or CICD pipeline is a group of practices of continuous integration and continuous delivery or continuous deployment. It is an approach where the DevOps team builds, tests, and deploys applications by enforcing automation. The CI/CD pipeline ensures more frequent and reliable updates to software applications. The principal goal of the CI/CD pipeline is to discover bugs earlier, boost the productivity of the development process, and provide faster release cycles.
11. Can you list out the common use cases of Jenkins?
Jenkins is popularly used in:
- Sanity/Smoke/CI/Regression test jobs
- Web/Data Scraping-related jobs
- Software build jobs
- General-purpose automation
- Reverse engineering jobs
- Code coverage measurement jobs
- Decoding jobs
12. Differentiate Jenkins and Bamboo.
The following table describes the key differences between Jenkins and Bamboo:
|Jenkins is an open-source automation server for continuous integration.
|Bamboo is a commercial automation server for continuous integration.
|It is compatible with Windows, macOS, and Linux systems.
|It is compatible with Windows, Solaris, and Linux systems.
|Jenkins supports Google Chrome, Firefox, and Internet Explorer.
|Bamboo supports Firefox, Microsoft Edge, Safari, and Google Chrome.
|It supports a wide range of plugins.
|It supports a limited number of plugins as compared to Jenkins.
|Jenkins is not up to the mark when it comes to user-friendliness.
|Bamboo is more user-friendly than Jenkins.
|It does not support built-in JIRA software integration, Git branching workflows, and Bitbucket server integration.
|It supports built-in JIRA software integration, Git branching workflows, and Bitbucket server integration.
13. Are there any prerequisites to using Jenkins? If yes, state them.
Yes, there are two major prerequisites to using Jenkins. These prerequisites are:
- We require an accessible source code repository, such as a Git repository.
- A working build script, such as the Maven script, is essential.
14. Can you tell the difference between Hudson and Jenkins?
The following table highlights the differences between Hudson and Jenkins:
|Hudson is an extensible continuous integration tool.
|Jenkins was forked from Hudson.
|It supports comparatively fewer plugins than Jenkins.
|It supports a wide variety of plugins.
|Hudson does not support continuous delivery.
|Jenkins supports continuous delivery.
|It integrates with various popular version control tools, like Perforce, CVS, Git, and Subversion.
|It integrates with tools, like DataDog, Sauce Labs, and JBoss, and version control tools, like Mercurial, CVS, Git, and Subversion.
15. How do you install Jenkins?
We need to follow the steps mentioned below to install Jenkins:
- Since Jenkins is a Java-based automation server, we require Java, and we need to install Java Version 8.
- We need to download the Jenkins WAR file.
- To deploy the Jenkins WAR file, we need to install Apache Tomcat Version 9.
- After installing Apache Tomcat, deploy the Jenkins WAR file.
- Finally, install the list of plugins suggested by Jenkins.
16. What commands will you use to start, restart, and stop Jenkins manually?
Firstly, we need to open the command or console line and go to the Jenkins installation directory. Now, we use the below commands to start, restart, and stop Jenkins manually:
Start Jenkins: jenkins.exe start
Restart Jenkins: jenkins.exe restart
Stop Jenkins: jenkins.exe stop
17. What do you know about Groovy?
Groovy is a Java-syntax-compatible object-oriented programming language for the Java platform. It is a native scripting language for Jenkins. Also, it is a dynamic and optionally typed language with static compilation and static-typing capabilities. It intends to boost a developer’s productivity with its easy-to-learn syntax.
18. What is a Jenkins job?
Jobs are the core of Jenkins’s build process. We can define a job or build job in Jenkins as a particular task or step in the entire build process. A job or build job could be running unit tests, compiling source code, deploying an application to the web server, etc. In addition, we can create and build these jobs to test java-based applications. Jenkins provides different types of build jobs, enabling users to create them based on needs.
19. Enlist and explain a few Jenkins build jobs.
The following are a few popular Jenkins build jobs:
- Freestyle Project: It is an unrestricted build job or task with multiple operations, such as a build, any script run, or pipeline run.
- Maven Project: If we want to manage and build projects containing the POM files, we need to use the Maven Project build job. Jenkins automatically selects the POM files, makes configurations, and runs a build.
- Multi-configuration project: It is ideal to use when we require different configurations, like running on multiple environments.
- Pipeline: It describes long-running projects that include several build agents.
- GitHub organization: It scans a user’s GitHub account for all repositories matching some defined markers.
20. Which source code management (SCM) tools does Jenkins support?
Jenkins supports the following source code management tools:
21. How do you move or copy Jenkins from one server to another?
There are multiple ways to copy Jenkins from one server to another. One approach is to copy the job’s directory from one server to another. To do this, you need to follow the steps mentioned below:
- Copy a job’s directory to move it from one installation of Jenkins to another.
- Make a clone of the existing job directory and assign a different name to it.
- Finally, rename the existing job directory.
22. What do you understand about Jenkins Pipeline?
A pipeline in Jenkins is a collection of events of jobs interconnected with each other in sequential order. The Jenkins pipeline is a suite of plugins that integrate continuous delivery pipelines into Jenkins. Alternatively, we can define the Jenkins pipeline as a series of tasks or events carried out in a particular sequential order to transform the code from version control into a stable software product using a set of plugins in Jenkins.
Intermediate-Level Jenkins Interview Questions
23. Can you explain how to create a backup and copy files in Jenkins?
If we want to create a backup and copy files in Jenkins, we need to periodically backup the JENKINS_HOME directory. This directory contains the following information:
- Configurations of all build jobs
- Configurations of slave nodes
- Build history
To create a backup of the Jenkins setup, just copy the JENKINS_HOME directory. In addition, we can copy a job directory to replicate or clone a job or rename the directory.
24. Can you explain how to create build jobs in Jenkins?
We can create build jobs in Jenkins using the below steps:
- Firstly, go to the Jenkins page, click ‘New Job’, and select ‘Build a free-style software project’.
- We need to specify the details of the newly created job, such as the source code management tool, triggers, build script, and other advanced options, such as steps to collect information out of the build and notify other people or systems of the build result.
- It is necessary to specify the location of the files that should be built.
- After marking all the settings, click on ‘Add build set up’. Now, we need to select an appropriate option here. For example, if we wish to build a file, we need to select the file name with the build command.
- Finally, click on ‘Build now’ to save the build and perform a test run.
25. How will you secure Jenkins?
We can secure Jenkins with the following steps:
- Initially, we need to ensure that global security is on.
- Later, we need to verify whether Jenkins is integrated with the intended company’s user directory using an appropriate plugin.
- Now, we have to ensure that the matrix or Project matrix is enabled to fine-tune access.
- Using the custom version-controlled script, we can automate the process of setting rights or privileges in Jenkins.
- Next, we need to limit the physical access to Jenkins data/folders.
- Lastly, we have to run security audits periodically on Jenkins data/folders whose physical access is limited.
26. Enlist the types of pipelines in Jenkins.
There are three types of pipelines in Jenkins, as listed below:
- CI/CD pipeline
- Scripted pipeline
- Declarative pipeline
27. Can we clone a Git repository via Jenkins? If yes, then how?
Yes, we can clone a Git repository via Jenkins. To do so, we need to enter the email id and username for our Jenkins system, switch to ‘job directory’, and run the ‘git config’ command for that directory.
28. How will you deploy the custom build of a core plugin?
The following are the steps to deploy the custom build of a core plugin:
- Firstly, stop Jenkins.
- Now, copy the .hpi file to $JENKINS_HOME/plugins.
- Delete the previously expanded plugin directory.
- Next, create an empty file called <plugin>.hpi.pinned.
- Finally, restart Jenkins and use the custom build of a core plugin.
29. Explain terms Agent, Jenkins Controller, and JenkinsFile.
Agent: An agent in Jenkins is a container or a machine connected to the Jenkins controller and performs tasks as instructed by the Jenkins Controller.
Jenkins Controller: It is a central and coordinating process that stores configurations, loads plugins, and renders different user interfaces for Jenkins.
JenkinsFile: The JenkinsFile is a text file that stores the definitions of all pipelines.
30. What are the different build statuses in Jenkins?
The following are the different build statuses in Jenkins:
- Aborted: The build got interrupted before it reached its expected end. For example, the build gets interrupted when the user stops it manually, or there is a timeout.
- Failed: The build has a fatal error.
- Stable: The build was successful and no publisher reported it as unstable.
- Successful: The build has no compilation errors.
- Unstable: The build is unstable if it is built successfully, but a few publishers report it as unstable and it has one or more errors that are not fatal.
31. What is the syntax to schedule a build job or SVN polling with Jenkins?
We need to use the cron syntax to schedule a build job or SVN polling. The cron syntax is represented by five asterisks, each separated by a space. The cron syntax is given below:
|[minutes] [hours] [day of the month] [month] [day of the week]
32. Do you know how Jenkins authenticates users?
Jenkins authenticates users in three different ways, as listed below:
- The default way Jenkins uses to authenticate users is by storing user data and credentials in an internal database.
- The second way is to configure Jenkins to leverage the authentication mechanism specified by the application server on which Jenkins is deployed.
- Configure Jenkins to authenticate against the LDAP server.
33. How will you use a third-party tool in Jenkins?
The following are the steps to use a third-party tool in Jenkins:
- Initially, install the third-party tool that we need to use in Jenkins.
- Download and install the plugin that supports our third-party tool from the Jenkins admin console.
- Now, we need to go to the ‘manage’ in the admin console and configure the third-party tool in the ‘Tools’ tab.
- Finally, use the installed plugin from the Jenkins build job.
The above process of using third-party tools may slightly vary for every different tool because of the difference in configuration settings.
34. Enlist a few Jenkins environment variables that you need to use in a shell script or batch file.
The following are the default Jenkins environment variables to use in a shell script or batch file:
As we configure new Jenkins plugins, more environment variables become available. For instance, when we configure the Jenkins Git plugin, the Git environment variables, such as $GIT_COMMIT and $GIT_URL, become available to use in a shell script or batch file.
35. What do you understand about the Jenkins Job DSL plugin?
The Jenkins Job DSL (Domain-specific language) plugin consists of two parts. One is a domain-specific language itself that enables users to use Groovy-based language to describe jobs. The other part is the Jenkins plugin that manages scripts and the updates of a Jenkins job.
Advanced-Level Jenkins Interview Questions
36. Explain the process of creating a multibranch pipeline in Jenkins.
The process of creating a multibranch pipeline in Jenkins is described below:
- Firstly, open the Jenkins dashboard and click on ‘new item’ from the top left of the screen to create a new item.
- Enter the project name, and from the options displayed, choose ‘Multi-branch pipeline’ and hit OK”.
- Now, select the repository location, branch source, and credentials for the branch source.
- Save the project and Jenkins will automatically generate Multibranch pipelines for repositories having branches and pull requests containing Jenkins files.
37. Explain the process of integrating Git with Jenkins?
We need to follow the steps mentioned below to integrate Git with Jenkins:
- Initially, we need to create a new job in Jenkins and then go to the Jenkins dashboard.
- We need to enter the project name on the dashboard, select the job type, and click ‘OK”.
- Now, we need to enter the project information.
- Go to the ‘source code management’ tab and check for the ‘Git’ option. There we will notice the ‘Git’ option if the Git plugin is already installed.
- If we do not notice the ‘Git’ option, we need to reinstall the plugins, such as GitHub plugin, GitHub Branch Source plugin, GitHub API plugin, and Gitclient plugin.
- Once we install plugins, we need to restart the Jenkins to reflect the changes.
- Finally, we have to enter the repository URL to pull the code from GitHub.
38. What are the two ways to configure the Jenkins node to communicate with the Jenkins Master?
The following are the two ways to configure the Jenkins node to communicate with the Jenkins Master:
- Browser: If we launch the Jenkins Node from a browser, a JNLP (Java Web Start) file gets downloaded. This file is responsible for launching a new process on the client machine to execute jobs.
- Command-line: To start the node agent using the command line, the client requires an executable agent.jar file. When this file runs, it launches a process on the client to communicate with the Jenkins Master to run build jobs.
39. Can we run automated tests in Jenkins? If yes, how?
Yes, we can run automated tests in Jenkins. We can use test automation tools like Selenium or Maven to automate tests in Jenkins. Using such tools, developers can schedule tests, and Jenkins displays test results and provides reports of test results to developers.
40. What will you do if your project build breaks?
We can fix or resolve our project build using the following two approaches:
- Open the console output for the broken project builds and check if any file changes are missed. If they are missed, place those file changes correctly.
- The other approach is to clean and update the local workspace to replicate the problem on a local setup to fix and resolve the issue.
41. Can you state the use of the JENKINS_HOME directory?
The JENKINS_HOME directory stores all the settings, logs, and configurations.
42. What do you understand about the backup plugins in Jenkins?
As its name suggests, the backup plugin in Jenkins backs up all critical settings and configurations that we may need for future use. It is the most useful plugin in case of failures so that we don’t lose the settings and configurations.
43. Can you tell about Kubernetes? How to integrate Kubernetes with Jenkins?
Kubernetes , also known as K8s, is an open-source container orchestration system that automates the deployment, scaling, and management of containerized applications. It groups containers that make up an application into logical units for easy management. We can use the Kubernetes deploy plugin to use Jenkins for continuous deployment.
44. Can you explain the difference between Ant, Maven, and Jenkins?
The following table highlights the differences between Ant, Maven, and Jenkins:
|Ant is a Java library and a command-line tool.
|Maven is a build automation tool primarily used for Java projects.
|Jenkins is an open-source automation server.
|The well-known usage of Ant is the build of Java applications. Its primary objective is to drive processes described in build files.
|The primary goal of Maven is to provide developers with a comprehensive model for projects and plugins or tools to interact with that model.
|It automates the software development process and facilitates continuous integration and continuous deployment.
45. Explain the critical aspects of the Jenkins Pipeline.
The following are the critical aspects of the Jenkins Pipeline:
- Pipeline: It is a user-defined model of the continuous delivery (CD) pipeline. A pipeline’s code defines the entire build process, i.e., it defines various stages for building, testing, and delivering an application.
- Node: It is a machine, which is a part of the Jenkins environment, and it executes a pipeline.
- Step: It is an individual task that tells Jenkins what to do at a particular point in time.
- Stage: It is a subset of distinct tasks performed through the build, test, and deploy stages of the pipeline.
46. How to configure Jenkins with Maven?
We need to follow the below-mentioned steps to configure Jenkins with Maven:
- Go to ‘Manage Jenkins’ and choose ‘Configure System’ on the Jenkins dashboard.
- Now, go to the Maven section and select ‘Add Maven’.
- We will notice the ‘Install Automatically’ box and uncheck it.
- Add the name for the setting and location of MAVEN_HOME.
- Save the name, and after that, one can create a job with the ‘Maven Project’ option.
47. Can you explain the steps to create a slave node in Jenkins?
Here are steps to create a slave node in Jenkins:
- Go to ‘Manage Jenkins’ and scroll down until you notice the ‘Manage Nodes’ section.
- Click on the ‘New Node’ option.
- Now, set the name node, pick the Dumb slave option, and click ‘OK’.
- Finally, enter the node slave machine details and click on the ‘Slave’.
48. How to configure Docker in Jenkins?
Following are the steps to configure Docker in Jenkins:
- Go to the Jenkins dashboard and click on the ‘Manage Jenkins’ option.
- The configuration page appears, and we need to select the ‘Manage Plugins’ option.
- Next, click on ‘Available’ to see the list of all available Jenkins plugins for installation.
- In the search box, search for the Docker plugin and select it.
49. What are the ways to trigger a Jenkins job?
The following are the different ways to trigger a Jenkins job:
- Trigger it manually from the Jenkins web application.
- Time-based scheduled triggers like a cron job.
- Trigger an API (POST) request with the required data to the target job URL.
- Event-based triggers, like SCM, WebHooks, etc.
- Trigger it using Jenkins CLI from the master/slave nodes.
- Upstream/downstream triggers by other Jenkins jobs.
50. Which credential types does Jenkins support?
Credentials in Jenkins are a set of information that ensures the authentication with internal and external services to execute an action. Jenkins has a Credentials Binding plugin that manages and provisions Jenkins credentials. The following are the different credential types that Jenkins support:
- Secret Text
- Username and Password
- Secret File
- SSH Username with a private key
- Docker Host Certificate Authentication
Jenkins is one of the widely used Java-based automation servers. It is used to continuously build and test software applications and to make it easier for developers to integrate changes to software applications. In general, Jenkins facilitates continuous integration and continuous delivery.
This article has covered the most commonly asked Jenkins interview questions and their detailed answers. You can ace your next Jenkins interview by becoming familiar with this set of Jenkins interview questions.
Also, if you have come across Jenkins interview questions other than the ones listed above, feel free to share them down in the comments section.
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