Top Jenkins Interview Questions and Answers

Top Jenkins Interview Questions and Answers

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Updated on Jan 24, 2022 21:34 IST

Be it monitoring the repeated task during a development project or identifying the errors or bugs in the initial stages of product development, Jenkins has emerged as a popular tool for every software development company. Thus, it is not a surprise that when you appear for a DevOps interview, the interviewer can ask you questions related to Jenkins. To help you crack the upcoming interview round, we have listed the most frequently asked Jenkins interview questions and answers. 

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Top Jenkins Interview Questions

Here is the list of the most important interview questions on Jenkins. This basic to advanced Jenkins interview questions guide will be useful for both fresher and experienced professionals.

Q1. What do you know about Jenkins?

Ans. Jenkins, which is written in Java, is a free open source continuous integration tool and automation server. It is designed to monitor continuous integration and its delivery. Jenkins automates the software development process and is integrated into each step of the software development lifecycle.

With the help of different plugins used for several software development stages, Jenkins accomplishes continuous integration.

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Q2. What is Continuous Integration?

Ans. It is a practice used in the development in which as soon as the developers commit the changes in source code, software testing is initiated. Once the testing phase is clear, the build goes for deployment. Once the deployment stage is successful, code is sent for production. Thus this is a continuous cycle in which commit, build, test, and deploy stages are recurring. Hence, it is called continuous integration or continuous deployment. The pipeline of continuous integration consists of tools that help in the host, monitor, compile, and test code.

Q3. What is Distributed Builds Architecture in Jenkins?

Ans. Jenkins master has its own executors and resources, which can be operated on their own and can execute and manage the built environment. However, with this ‘standalone’ configuration, one can run out of resources as soon as the total number of projects increases. Thus, it is not a good option to run the build on central machines. Hence, in such situations, the concept of distributed build architecture comes into the picture.

Through this, the users need to configure the Jenkins machines to be slave machines so that they can easily handle the load of the master Jenkins server.

Here, the slave is a computer on which the unload build projects set up is done to distribute the build task. In this method, either one can stick to a specific machine for a particular build, or they might choose to roam between multiple slaves. It is also termed master and  slave machines.

Steps in which the Distributed Architecture of Jenkins Works:

 

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Q4. What is AWS Secrets Manager?

Ans. It is a precise solution for securing secret storage. In AWS Secrets Manager, one can define any secret for the AWS account just for once, and later, they can give permissions to the users for using this secret. It integrates with other AWS services like:

  • Secret entry management
  • Secret value management
  • Access control
  • Secret encryption
  • Auditing

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Q5. How is Jenkins different from Bamboo?

Ans. Both Jenkins and Bamboo are continuous integration tools used for agile development. Also, both have the same starting point, i.e. create a plan outlined with a series of tasks. However, they have minor yet crucial differences, and depending upon the business, budget, user interface, plug-ins, and configuration, one can choose between them.

Jenkins Bamboo
Open-source Not open source
Free Different charges for build agents
Supports Windows, Ubuntu, Red Hat, Mac Operating systems Supports Windows, Linux, Solaris Operating systems
Works on browsers like Chrome, Firefox, Internet Explorer Works on browsers Firefox, Chrome, Safari, Edge
Multiple plug-ins are available Fewer plug-ins
Various communities support it as it is open source Less support

Q6. Is there any prerequisite for Jenkins?

Ans. To use Jenkins, one requires two things:

  • Source code repository like Git repository
  • Build script like Maven script

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Q7. Do you think Jenkins is better than Jira?

Ans. Jira is software used by agile teams for project planning, tracking, and managing. Through Jira, one can customize their workflows, collaborate with teams, and release software. It is also known as the incident management tool. Professionals working in the software project development team, help desk system, etc. use Jira for bug tracking. Below is the concept of Jira.

 

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However, when compared with Jenkins, Jira’s UI is difficult to navigate. Whereas, Jenkins’ easy to deploy configuration and its automatic rollback features attract various users. It is also the best option for conducting continuous builds.

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Q8. List down some essential plugins of Jenkins.

Ans. Below is the list of popular Jenkins plugins:

Jenkins Plugins Monitoring Performance Enhancers Scaling Jenkins Setup Source Control Management (SCM) Other Essential Plugins
Dashboard View Plugin Monitoring Plugin Performance Plugin Kubernetes Plugin SCM API Maven 2 project
View Job Filters Plugin Metrics Plugin Performance Publisher Plugin Amazon ECS Container Service Git Plugin HTML publisher
Folders Plugin Jenkins CI Build Monitor Plugin Performer Enhancer Plugins Self-Organizing Swarm Modules Plugin GitHub Integration Plugin Copy artifact

Q9. Define the significance of running Selenium tests in Jenkins.

Ans. Below are some of the benefits of running the Selenium test in Jenkins:

  • Whenever software is updated, it allows you to run tests and deploy it to a new environment when it passes the test
  • With Jenkins, test scheduling is possible
  • It will enable you to save all the execution history and test reports
  • Maven is integrating with Jenkins, which helps in building and testing projects with continuous integration

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Q10. What is Maven?

Ans. Maven is a build management tool that works on the concept of the Project Object Model (POM). It includes Jenkins’ project information and configuration information, including:

  • Construction directory
  • Source directory
  • Dependency
  • Test source directory
  • Goals
  • Plugins

Maven is also known as the replacement for Ant (earlier Jenkins was used Ant instead of Maven) as it overcomes issues that Ant had before.

Q11. Why is Maven with Jenkins the right combination?

Ans. Maven uses pom.xml to configure build, test, and run dependencies. It also works well in managing the entire lifecycle of the test project. Once Maven gets integrated with Jenkins, the Maven Webdriver executes all the tests and builds the project effectively.

Q12. How is Jenkins different from Maven?

Ans. Jenkins uses Maven as its build tool, helping in continuous integration. Below are the key differences:

Jenkins Maven
Continuous Integration tool Build tool
Helps in software testing and reporting Helps in build and version control
Introduced in 2011 Introduced in 2004
Plugins help in adding projects written in languages other than Java Plugins help in software build, test, source control management, running a web server, etc.

Q13. Name some of the prominent features of Jenkins.

Ans. Below are some Jenkins features:

  • Free open-source tool
  • Supported by the various operating system
  • Pipeline support
  • Fast release cycle
  • Quick and easy configuration
  • Supports third-party plugins
  • Test harness works using JUnit

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Q14. Why do developers prefer using Jenkins?

Ans. Jenkins is among the prominent CI tools, and some of the benefits of using Jenkins are:

  • It meets the needs of developers and has scope for continuous improvement.
  • It supports various plugins that multiply the power of Jenkins.
  • Jenkins is flexible with a cloud environment that helps in building cloud-native applications.
  • It gives the option to define and schedule the task and builds triggers.
  • It is easy to customize Jenkins as per the requirements of developers.

Q15. How does using Jenkins for Test Automation benefit developers?

Ans. Some of the benefits of using Jenkins for test automation are:

  • Opens up an option for scheduling test automation.
  • Developers get detailed insights on test failures.
  • Gives detailed information on test results and trends.

Q16. Name some system requirements for installing Jenkins.

Ans. Below are some of the prerequisites to install Jenkins:

  • RAM – 256MB
  • Space – 1 GB of drive
  • Language – Java
  • Browser – Web browser

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Q17. Which is the native scripting language used in Jenkins?

Ans. Groovy from Apache, which is a Java-based language, is used as the native scripting language in Jenkins. It improves the performance of Jenkins, and its excellent interface is dynamic and compatible.

Q18. What do you mean by the Jenkin pipeline?

Ans. Several interlinked jobs placed in a particular sequence are termed as a Jenkins pipeline. It includes several plug-ins that integrate and implement the delivery. There are three different types of Jenkins pipelines:

  • CI (Continuous Integration)/CD (Continuous Delivery) pipeline
  • Scripted pipeline
  • Declarative pipeline

Q19. What is CRON?

Ans. CRON is a syntax used to schedule a Build job or SVN polling in Jenkins. It is exhibited by five asterisks separated by a space. The syntax is written in the format – Minute Hour Dom Month Dow.

Q20. What do you mean by * */1 * * *?

Ans. It means that the CRON syntax will execute the job every minute and if someone wants to implement the job every hour like at 07:00, 08:00, 09:00, and so on, one can use the syntax – 0 * * * *

Q21. Give steps for including third-party tools in Jenkins.

Ans. Below are the steps:

  • Install the third-party tool
  • Introduce the Jenkins module via Jenkins administrator console, which supports the tool
  • Ensure to arrange the tool in the Tools Tab and Manage Jenkins area in the Jenkins administrator console
  • Utilize the plug-ins from Jenkins build job

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Q22. How to create global macros and templates in Jenkins’s job builder?

Ans.

Jenkins

—global-defaults.yaml

—global-macros.yaml

—global-templates.yaml

—projectfolderA

| —projectA.yaml

Q23. Define the steps to create a backup and copy files in Jenkins.

Ans. Below are the easy steps to create backup and copy files in Jenkins:

  • Periodically create the backup of “JENKINS_HOME” directory
  • Use CRON job or “Thin Backup” plugin in Jenkins
  • Jenkins Home directory will store all configurations

Q24. Which SCM tools are supported in Jenkins?

Ans. Below is the list of SCM tools:

  • Git
  • Subversion
  • CVS
  • Mercurial

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Q25. Define Kubernetes.

Ans. It is a container orchestration tool used to create multiple container instances to achieve fault tolerance. This plugin can be used for ensuring continuous deployment.

Q26. What is Jenkins Multibranch Pipeline? What are the steps to create a Jenkins Multibranch Pipeline?

Ans. A Jenkins Multibranch Pipeline is a concept that enables developers to implement different Jenkinsfiles for different branches of the same project. It allows users to automatically create a pipeline for each branch on the source control repository. 

It works using Jenkinsfile (a pipeline script that defines your CI/CD pipeline) that is usually stored inside a Source Code Management (SCM) like GitHub, BitBucket, etc. Jenkins automatically discovers, manages, and executes Pipelines for branches that contain a Jenkinsfile in source control. 

 

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Below are the steps to create a Jenkins Multibranch Pipeline:

  1. Open Jenkins UI
  2. Click New Item on Jenkins home page 
  3. Enter a name for your Pipeline, select Multibranch Pipeline, and click OK 
  4. Select branch source option, click on ‘add source’, and select Git option
  5. Enter the Project Repository name and Credentials (for a private account)
  6. Save the Multibranch Pipeline project

Q27. Name some Jenkins built-in environment variables.

Ans: Here are some of the built-in environment variables:

Jenkins built-in environment variable Description
BUILD_NUMBER Current build number
BUILD_ID The current build ID
JOB_NAME Name of the project of this build
JENKINS_URL  URL of Jenkins
BUILD_URL Full URL of the build
JOB_URL  Full URL of the job
NODE_NAME  Name of the slave or master

Q28. How to trigger a Jenkins Job/Pipeline?

Ans. Below are the different ways to trigger a job/pipeline in Jenkins:

  1. Manually from the Jenkins web application.
  2. Using an API POST.
  3. Using Jenkins CLI from the master/slave nodes.
  4. Time-based Scheduled triggers.
  5. Event-based triggers.
  6. Upstream/downstream triggers.

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Q29. What are the various ways in which build can be scheduled in Jenkins?

Ans. Below are the ways to schedule build in Jenkins: 

  1. By source code management commits
  2. After the completion of other builds
  3. At a specified time (CRON jobs)
  4. Manual Build Requests

Q30. What are the credential types supported by Jenkins?

Ans. Some of the credential types supported by Jenkins include:

  1. Secret text – A token such as an API token, JSON token, etc.
  2. Username and password – Basic Authentication with a username and password pair.
  3. Secret file – A secret file with binary content and an optional filename used to authenticate some secure data services.
  4. SSH Username with a private key – An SSH public/private key pair for Machine to Machine authentication.
  5. Secret source – It allows JCasC to interpolate string secrets from Secrets Manager.
  6. Certificate – A PKCS#12 certificate file encrypted with a zero-length password.

Q31. What is In-process Script Approval? How does it work?

Ans. The In-process Script Approval is a Jenkins process that improves the security of the overall Jenkins ecosystem. This process must be done only once for each new environment variable used in a Jenkins pipeline.

Here’s how the In-process Script Approval process works:

Jenkins enables users to execute Groovy scripts in Jenkins. The plugins execute user-provided scripts in a Groovy Sandbox that limits what internal APIs are accessible to protect Jenkins from the execution of malicious scripts. This protection is provided by the Script Security plugin. When an unsafe method is used in any of the scripts, the In-process Script Approval action will appear in Manage Jenkins. This enables administrators to make a decision about which unsafe methods should be allowed in the Jenkins environment. 

Q32. How to achieve continuous integration using Jenkins?

Ans. Below are the steps to achieve continuous integration using Jenkins:

  1. Developers commit their source code changes to the shared Git repository.
  2. The shared Git repository is inspected by the Jenkins server at specified intervals. Changes identified are taken into the build.
  3. The build results and test results are shared with the developers.
  4. The built application is displayed on a test server and automated tests are run.
  5. A clean and tested build is deployed to the production server.

Q33. What are the different ways for configuring user authentication in Jenkins?

Ans. Jenkins authenticates users in the following ways: 

  • Delegate to the servlet container

Jenkins is configured to use the authentication mechanism defined by the application server on which it is deployed. 

  • Jenkins’ own user database

Jenkins’s own built-in user data store is used for authentication instead of delegating to an external system. This is ideal for smaller environments and is enabled by default with new Jenkins 2.0 or later installations.

  • LDAP

All authentication is delegated to a configured LDAP server, including both users and groups. This is used for larger installations in organizations that already have configured an external identity provider. 

Q34. What is DSL Jenkins?

Ans. DSL stands for Domain Specific Language. Jenkins DSL is a plugin that makes it easier to manage jobs. It allows us to define jobs in a programmatic manner that is human readable. This plugin intuitively translates the UI configurations into code. It enables developers to create a version for the job and also maintain the history of the changes. The converted code is in a Groovy-based language.

In a nutshell, it allows the programmatic generation of Jenkins jobs using Groovy code. Developers can store this code in their Git repository and create Jenkins jobs automatically. 

Q35. How to configure the Jenkins node agent to communicate with Jenkins master?

Ans. We can configure the Jenkins node agent to communicate with the Jenkins master in the following two ways: 

1. Browser

When the Jenkins node agent is launched from a browser, a JNLP file is downloaded. This file launches a new process on the client machine to run jobs.

2. Command-line

In this, the client needs the executable agent.jar file. When this file is run, it launches a process on the client to communicate with the Jenkins master to run build jobs.

Q36. What is the difference between GitHub and Jenkins?

Ans. Jenkins create workflows through Declarative Pipelines that are almost similar to GitHub Action workflow files. GitHub Actions use jobs for grouping individual or multiple commands whereas Jenkins uses stage for running a number of steps.

Conclusion 

These were some commonly asked Jenkins interview questions. We hope these interview questions on Jenkins will help you ace your next interview.  

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This is a collection of insightful articles from domain experts in the fields of Cloud Computing, DevOps, AWS, Data Science, Machine Learning, AI, and Natural Language Processing. The range of topics caters to upski... Read Full Bio