Top 50+ Jenkins Interview Questions [2023]

Basic Jenkins interview questions

1. What is Jenkins?

Jenkins CI/CD tool is a popular open-source automation platform for developing, testing, and deploying software applications. It is a Continuous Integration (CI) and Continuous Deployment (CD) technology that aids in automating several stages of the software development lifecycle.

Jenkins provides a web-based interface for creating and managing jobs that can be run automatically or manually. It supports various project types and languages and can interface with other DevOps technologies like Git, Docker, Kubernetes, and others. Jenkins may be modified to suit practically any form of software development workflow because of its extensive ecosystem of plugins and extensions.

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2. What are the features unique features Jenkins provides?

Jenkins is simple to install and configure. Jenkins has a plethora of plugins that allow it a great deal of flexibility. It generates a report after deployment, indicates mistakes in code or tests, and discovers and addresses a variety of issues in near real time. Some of the key features of Jenkins are:

• Jenkins supports a variety of plugins as per the Jenkins community It supports 1500 plugins that help integrate other development tools with Jenkins, making it more convenient for build and source codes.
• It is a self-contained Java application that is unconcerned about the platform on which it runs. It is compatible with all standard operating systems, including Windows, Unix, and Mac OS. Jenkins' online interface is easy to set up and manage, including error checks and an integrated help feature.
• Jenkins is an open-source project that can be used for free. Jenkins has an active development community that meets in person and online regularly. This makes installation easier while limiting resources to a single computer, virtual machine, or container.
• Jenkins' plugin architecture allows it to be expanded in virtually any way, giving it nearly infinite potential.

3. Functional testing can be automated using Jenkins

Jenkins can be used to automate functional testing by combining it with a test automation framework capable of running automated functional tests, such as Selenium or Appium. Jenkins can be set up to run automated functional tests whenever a new build or code change is made and to create reports and notifications based on the test results.

4. Why is Jenkins used with Selenium?

Using Jenkins for Selenium testing can automate web application testing as part of their continuous integration and delivery pipeline. Developers and testers can write Selenium tests, check into version control, and run automatically by Jenkins as part of the build process. This allows for detecting problems and regressions early in the development cycle, making it easier to resolve issues before they reach production.

Note : Check out our dedicated blog on Selenium Jenkins integration

5. Can you explain Jenkins's architecture

Jenkins is a distributed system that can be set up to run on a single or several machines. Jenkins' architecture is made up of the following parts:

• Jenkins master: The Jenkins master is the central component of the Jenkins architecture. It oversees the entire build process, including build scheduling, workload distribution to build agents, and collection and reporting of build results.
• Build Agents: Build agents are worker nodes that run builds on the Jenkins master's behalf. Build agents can be installed on the Jenkins master's machine or on distant machines.
• Plugins: Jenkins plugins are extensions that can be installed to bring new functionality to the system. Jenkins has many plugins that help with various development, test, and deployment activities.
• Jenkins User Interface: For customizing and managing the build process, Jenkins provides a web-based user interface. A web browser can be used to access the user interface.
• Jenkins API: Jenkins provides a RESTful API for programmatically interacting with Jenkins. The API can automate processes like building triggers and getting build results.

Jenkins elements are assembled and interact as follows:

• Developers commit modifications to the repository's source code.
• The Jenkins CI server scans the repository at regular intervals and pulls any new code that becomes available.
• The code is built into an executable file by the Build Server. If the build fails, the developers receive feedback.
• Jenkins is responsible for deploying the build application to the test server. The developers are notified if the test fails.
• The tested application is deployed on the production server if the code is error-free.

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Also, subscribe LambdaTest Youtube Channel to get updated about the software testing domain and learn in detail about different automation testing such as Selenium testing, Cypress testing, Playwright testing, and much more

CI/CD Interview Questions

Note : We have compiled all the CI/CD Interview Questions in here. Feel free to visit it. Check it out now!!

6. Explain the process of Jenkins

Here are step-by-step explanations to understand Jenkins Process:

• The first step is to download and install Jenkins on a server. This includes installing the necessary plugins, configuring user credentials, and configuring build agents and nodes.
• Define the various steps in the software development process by creating a job or pipeline.
• After creating the job or pipeline, it can be triggered manually or automatically. The user initiates manual triggers, whereas automatic triggers are set up to run at predetermined intervals or in response to specific events, such as code commits.
• Jenkins will begin the build process when the job or pipeline is triggered.
• It runs a suite of automated tests after the build is finished to ensure that the code meets the required quality standards.
• After passing the tests, Jenkins can deploy the application to the appropriate environment, such as a staging or production server.
• Jenkins can also collect and analyze metrics such as build time, test coverage, and code quality to provide insights into the software development process's performance.

7. What is Groovy in Jenkins?

Groovy is a very potent language with the capacity to perform nearly all of Java's operations, including the creation of sub-processes and the execution of arbitrary commands on the Jenkins controller and agents. Even files that the Jenkins controller has access to on the host (like /etc/password) can be read by it.

Several jobs in Jenkins can be carried out through Groovy scripts, including

• Making and setting up pipelines and jobs in Jenkins
• Building and deploying builds
• Analyzing test and building results
• Notification and alarm transmission
• Performing cleanup and maintenance activities after construction

8. Mention the commands you can use to start Jenkins manually.

To start Jenkins manually, open the Console/Command line and navigate to your Jenkins installation directory. You can use the following commands over there:

• jenkins.exe start
• jenkins.exe stop
• jenkins.exe restart

9. What are the system requirements to install Jenkins?

The minimum configuration required is

• 256MB of RAM
• 1 GB of drive space
• Java
• Web browser

10. Which SCM tools Jenkins supports?

Jenkins is compatible with a variety of Source Code Management (SCM) tools, including

• Git
• Subversion (SVN)
• Mercurial
• Perforce
• ClearCase
• CVS
• AccuRev
• RTC (Rational Team Concert)
• TFS (Team Foundation Server)
• Bitbucket

11. Explain the post in Jenkins.

A post section is a pipeline block in Jenkins that allows you to define steps that should be executed after the main build pipeline has been completed. The post section can be used to define steps for tasks like sending notifications, archiving artifacts, and cleaning up the workspace.

Syntex to define post in Jenkins can be defined as below:

pipeline {
  // Define the stages of the pipeline here
  stages {
      // Define the build stages here
  }


  post {
      // Define the post-build actions here
  }
}

12. Which commands can be used to begin Jenkins?

The commands to start and stop Jenkins may change depending on the operating system and how Jenkins was installed. Some typical commands that can be used to launch Jenkins are listed below:

To start Jenkins on systems that use systemd, such as Ubuntu 16.04 and later, enter the following command:

sudo systemctl start jenkins

Use the following command to launch Jenkins on systems that make use of SysV init, such as CentOS 6. x and earlier:

sudo service jenkins start

Use the following command to launch Jenkins for running in a Docker container:

docker start <jenkins_container_name>

Also, check out this tutorial: "Cypress Docker: A Step-by-Step Guide With Examples" for a practical guide on using Cypress with Docker.

13. What are the common use cases Jenkins is used for?

Jenkins is used for various development and deployment tasks, and it has a huge plugin ecosystem for different usages. Here are some of the most common uses case of Jenkins:

Continuous Integration (CI): Jenkins is frequently used for Continous Integration, which automates the process of building, testing, and packaging code changes as they are committed to a version control system.

Continuous Delivery/Deployment (CD): Jenkins can also be used for continuous delivery/deployment (CD), which automates deploying code changes to production environments.

Automated Testing: Testing that is automated: Jenkins can be used to automate a variety of testing processes, including unit testing, functional testing, and performance testing. Jenkins integrates with many testing frameworks and tools, making the creation of automated testing pipelines simple.

DevOps Automation: Jenkins can be used to automate various DevOps tasks, such as infrastructure provisioning, configuration management, and application deployment.

Plugin Ecosystem: Jenkins has a robust plugin ecosystem that enables users to add new features and integrate them with a variety of tools and services, including version control systems, issue trackers, and cloud computing platforms.

14. What is "Continuous Integration" with reference to Jenkins?

Jenkins is a popular Continuous Integration tool that automates the process of building, testing, and packaging code changes as they are committed to a version control system. Jenkins automatically pulls the most recent code and runs a build and test process when a developer commits a change to the repository. If the build and tests run successfully, the code change is considered integrated and can be merged into the shared code repository.

Jenkins supports numerous build and test tools, including Ant, Maven, Gradle, JUnit, TestNG, and others. Jenkins can also be set up to run builds and tests in a variety of environments, such as virtual machines, Docker containers, and cloud platforms.

15. Explain the Jenkins pipeline?

A Jenkins pipeline is a means to use a domain-specific language (DSL) to define and automate a continuous delivery pipeline. It enables teams to specify the complete pipeline as code, making pipeline configurations easy to version, test, and share. Here is a graphical representation of the Jenkins pipeline.

A pipeline is made up of several stages, each of which represents a stage in the pipeline. Each stage may have one or more steps that outline the actions to be taken at that stage. A step can be a build command, a test command, or any other operation required along the pipeline.

16. What is Jenkins Multibranch Pipeline?

A multi-branch pipeline is nothing more than a collection of pipeline jobs. Jenkins will generate a folder for each branch you have. A multi-branch job could be used instead of establishing a pipeline task for each branch in a git repository. This implies you'll only have to create one job. You must also specify the location of the Jenkinsfile, which must be the same in all of the branches you generate.

Note : Learn in detail how to create a multi-branch pipeline in Jenkins.

17. Mention some of the useful plugins in Jenkins

Jenkins has a large plugin ecosystem that allows it to extend its functionality and interface with other tools and services. Here are some of Jenkins' most useful plugins:

• Git Plugin
• Pipeline Plugin
• Maven Plugin
• Docker Plugin
• Slack Plugin
• JIRA Plugin
• SonarQube Plugin
• Kubernetes Plugin

18. Which are the two components that Jenkins integrates the most?

Jenkins majorly integrates with this two-component:

• Jenkins may be connected with a variety of VCS systems, including Git, SVN, and Mercurial, to automatically build, test, and deploy code changes as they are committed to the repository.
• Jenkins may be linked with a variety of build and test tools, including Apache Maven, Gradle, Ant, JUnit, TestNG, and many others, to automate the build and test process and create test results reports.

19. How do you deploy a custom build of a core plugin?

Follow these steps to deploy a custom build of a core plugin in Jenkins:

• To begin, you must clone the source code of the core plugin that you wish to edit. The source code is available on the Jenkins GitHub site.
• Make the necessary code modifications and build the plugin with Maven. To build the plugin, you must have Maven installed on your machine.
• After building the plugin, you must stop the Jenkins server.
• Locate the "plugins" directory in the Jenkins home directory. Within this directory, look for a subdirectory called the name of the core plugin you want to alter.
• Delete the subdirectory containing the name of the core plugin to be modified.
• Transfer the freshly created plugin (the .hpi or .jpi file) to the "plugins" directory.
• Start the Jenkins server again.

20. What is a Jenkins job?

A Jenkins job is a unit of work that the Jenkins automation server executes. A job is a predefined sequence of tasks that Jenkins executes when triggered.

An administrator or developer configures and creates a job in Jenkins, which outlines the actions that must be completed when the job is activated. A job can be triggered manually or automatically based on particular events such as source code updates, a timer, or a user action.

21. How do you store credentials in Jenkins securely?

Credentials can be securely stored in Jenkins using the Credentials plugin, which stores various types of credentials such as - Username with a password, SSH username with the private key, AWS Credentials, Jenkins Build Token, Secret File/Text, X509 & other certificates, Vault related credentials securely with proper encryption & decryption as required.

Jenkins provides various ways for safely storing credentials:

• Make use of the built-in Credentials plugin.
• Encrypt critical files with the Secret File plugin.
• To inject credentials directly into jobs as environment variables or files, use the Credentials Binding plugin.
• To guarantee security, best practices such as restricting access, using strong passwords, and rotating credentials on a regular basis should be followed.

22. How can we stop a scheduled job from being executed temporarily?

You can disable a scheduled job in Jenkins to prevent it from being executed momentarily. Here's how to go about it:

• Log in as an administrator or a user with the relevant permissions to your Jenkins instance.
• Navigate to the Jenkins dashboard and find the job you wish to pause temporarily.
• To open the job's setup page, click on it.
• To temporarily disable the job, click the "Disable" button on the left-hand side of the page.
• When a job is disabled, its status changes to "Disabled" on the Jenkins dashboard, and it will not be executed until it is re-enabled.
• Simply click the "Enable" button on the job configuration page to re-enable the job.

Intermediate Jenkins Interview Questions

23. What are the ways to trigger a Jenkins Job/Pipeline?

In Jenkins, you can trigger Jobs or Pipeline with various methods some of the common methods are mentioned below:

• Manual Trigger: The simplest way to start a job is to use the "Build Now" or "Build with Parameters" options in the Jenkins dashboard or from the command line.
• Scheduled Trigger: You can schedule a job to run automatically at certain hours or on specific days using the Jenkins built-in scheduler.
• SCM triggers: Jenkins can monitor source code repositories like Git, SVN, or Mercurial for changes and immediately start a job when one is found.
• Webhook activate: On your code repository, you can configure webhooks to activate a Jenkins job when a specific event occurs, such as a push to the repository or creating a pull request.
• Remote Trigger: Using an HTTP POST request, you can utilize the Jenkins Remote API to trigger a job remotely. This is useful when combining Jenkins with third-party tools or services.
• Other Triggers: Jenkins also has other triggers such as build after other projects are built, build with parameters, build with the condition, and so on.

24. What is Jenkins Build Cause?

Jenkins Build Cause is a feature that lets you determine why a build was triggered. It describes the cause of a build, such as whether it was initiated directly by a user or automatically by a scheduled trigger, a code change, or an external event such as a webhook.

25. What are the Parameters in Jenkins?

Parameters in Jenkins refer to the inputs required when running a job or a build. They enable you to tailor the build process to specific scenarios and provide flexibility in how jobs are executed. There are several types of parameters, such as:

• String parameters
• Boolean parameters
• Choice parameters
• File parameters
• Password parameters

26. How to create a backup and copy files in Jenkins?

To create a backup, simply back up your JENKINS_HOME directory regularly. This section includes your build job configurations, slave node configurations, and build history. Simply copy this directory to create a backup of your Jenkins setup. You can also copy or rename a job directory to clone or replicate a job.

Another way is to use the ThinBackup plugin. It can back up Jenkins data, including configuration files, plugins, and job configurations. You can set the plugin to run regularly and backup data to a specific directory.

27. How does Jenkins know when and how to execute a Scheduled job/pipeline?

Jenkins executes scheduled jobs and pipelines using a built-in scheduler. The scheduler determines when and how frequently a job should run based on the configured schedule.

The schedule can be configured using the "cron" syntax, a popular scheduling format in Unix/Linux systems. The cron syntax is made up of five fields separated by spaces, which represent the minute, hour, day of the month, month, and day of the week.

The following cron syntax, for example, depicts a job that runs every weekday at 9:30 AM:

30 9 * * 1-5y

28. What are the Scopes of Jenkins Credentials?

Jenkins credentials can be of one of the three scopes- Global, System, or Folder

Global: the credential will be usable across all the jobs configured in the Jenkins instance (i.e. for all jobs). This is more suited for user Jobs (i.e. for the freestyle, pipeline, or other jobs) to authenticate itself with target services/infrastructures to accomplish the purpose of the job)

System: This is a special scope that will allow the Jenkins itself (i.e. the core Jenkins functionalities & some installed plugins) to authenticate itself to external services/infrastructures to perform some defined tasks. E.g., sending emails, etc.

Folder scope: Within a Jenkins instance, folder credentials are exposed to a specified folder and its child tasks and pipelines. They are saved in the Jenkins credentials store and can be used by any user or job with the relevant permissions inside that folder.

29. What credential types does Jenkins support?

Jenkins accepts a wide variety of credential types for safe authentication and access to a variety of systems and resources. Jenkins supports the following popular credential types:

• Username and password
• SSH username with private key
• Secret text
• Certificate
• Docker host certificate authentication
• Amazon Web Services (AWS) credentials
• Google Cloud credentials
• Kubernetes configuration (kubeconfig)
• GitHub personal access token
• SSH Agent credentials
• Jira Site credentials
• GitLab personal access token
• Vault token

And many more.

30. What is a Jenkins Shared Library, and why is it useful?

Jenkins Shared Library is a valuable tool that allows you to share code and functionality between pipelines and tasks in your Jenkins installation. It allows you to define reusable code in one place that numerous pipelines and processes can use without duplicating the code.

The following are some of the advantages of using a Jenkins Shared Library:

• Code reusability: In a centralized location, you may define reusable code that various pipelines and jobs can utilize without duplicating the code.
• Consistency: By ensuring that your pipelines and jobs use the same version of the code, you can ensure consistency and reduce errors.
• Versioning: Your Shared Library code can be versioned, allowing you to utilize multiple versions of the same code in different pipelines and processes.
• Simplified Pipeline code: Pipeline code can be simplified by abstracting difficult logic into the Shared Library, making your pipelines easier to read and manage.

31. What is the Blue Ocean?

Blue Ocean is a modern and user-friendly Jenkins user interface that makes creating, visualizing, and interacting with pipelines and jobs easier. It is a Jenkins plugin that provides a web-based dashboard for managing pipelines and jobs in a more user-friendly and visually appealing manner.

Some of the features of Blue Ocean are:

• Graphical representation of your pipelines, making it easier to see the status of each stage and understand the pipeline flow.
• Visual editor that allows you to drag-and-drop pipelines to design, edit, and customize them.
• View the history of your pipelines in a more user-friendly and interactive manner, including the option to view extensive logs and check the status of each stage.
• Visualizations and analytics to assist you in analyzing the performance and health of your pipelines.

32. What is the Jenkins User Content service?

Jenkins User Content service is a feature in Jenkins that allows users to upload and save files directly from their builds, such as build artifacts, logs, and reports. The files are saved in a dedicated directory in the Jenkins home directory, which users and build tasks can access.

Administrators can put files in the $JENKINS_HOME/userContent folder, which is served from yourhost/jenkins/userContent.

33. What is Artifact Archival, and how does it work in Pipelines?

Artifacts are files generated by a build task that must be saved for future references, such as built binaries, test reports, and other generated files, in Jenkins. Archiving these artifacts in a repository or storage site so that they may be conveniently retrieved and used in future builds or deployments is known as artifact archival.

The "archiveArtifacts" step in Jenkins Pipelines can be used to archive artifacts. Here is an example:

pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        // Compile and generate artifacts
        sh 'make'
       
        // Archive the generated artifacts
        archiveArtifacts artifacts: 'build/**/*.jar', fingerprint: true
      }
    }
  }
}

34. What is Agent in Jenkins?

An agent in Jenkins is a worker node that is in charge of executing a specific build or job. An agent is a separate computer or virtual machine dedicated to performing specific tasks for a Jenkins job.

When a Jenkins job is triggered, it is assigned to a nearby agent, which then executes the build on its own hardware or virtual environment. Jobs can be distributed across multiple machines, increasing the speed and efficiency of the build process.

There are mainly two types of agents in Jenkins: Master and Slave.

35. What is Jenkinsfile?

Jenkinsfile is a text file that defines the whole Jenkins Pipeline construction process. It's written in a domain-specific language (DSL) and contains the instructions Jenkins needs to build, test, and deploy software.

36. Differentiate between Maven and Jenkins.

37. What is the difference between Bamboo and Jenkins?

Here is the table comparing Bamboo vs. Jenkins to understand the difference between Them.

38. What is the process of integrating Git with Jenkins?

Here are steps you can unfollow to integrate Git with Jenkins:

• Open GitHub Repository and click on “Setting”.
• In Settings, you will find “webhook”; click on “add webhook”
• Once you get “Add webhook’, add jenkins environment URL as Payload URL and Add “application/jason” in Content-type.
• 'Which events would you like to trigger this webhook?' page Select 'Let me choose individual events.' Then select 'Pull Requests' and 'Pushes'. At the bottom of this option, tick the 'Active' box and then click 'Add webhook'.
• Open jenkins, click “new item,” and find the “source code management” tab.
• Click on Git and enter the URL to your GitHub repository in the 'Repository URL' column.
• Select the 'GitHub hook trigger for GITScm polling' option from the 'Build Triggers' menu. Alternatively, select your preferred trigger.

That is how you can integrate your GitHub repository with the Jenkins project.

39. how can you integrate Jenkins with Kubernetes?

When Jenkins is integrated with Kubernetes, teams may automate the deployment of containerized apps to a Kubernetes cluster. Jenkins may be used to build and test application code, as well as produce container images and deploy them to the Kubernetes cluster.

Here is an overview of how can you connect Kubernet with Jenkins:

• Go to the Jenkins Plugin Manager and search for "Kubernetes" to install the Kubernetes plugin.
• Provide the Kubernetes API server URL, credentials, and the Kubernetes namespace where the Jenkins agent pods will be deployed.
• If one does not already exist, create one. This can be done on a public cloud provider such as Google Cloud, Amazon Web Services, or Microsoft Azure, as well as on a private infrastructure.
• Specify the Kubernetes pod template to be used for the job in the Jenkins job settings. The Docker image to be utilized, any environment variables, and volume mounts are all included.
• After configuring the Jenkins task, execute it to develop and test the application code, create a container image, and deploy it to the Kubernetes cluster.

40. What is DSL Jenkins?

In Jenkins, DSL (Domain-Specific Language) refers to the ability to define Jenkins jobs as code using a dedicated programming language rather than the Jenkins web interface. Jenkins' DSL enables developers and DevOps engineers to create their build, test, and deployment pipelines by writing code in a language familiar to them, such as Groovy.

DSL in Jenkins can be used in two main ways:

• The Job DSL plugin allows you to define Jenkins jobs straightforwardly and flexibly using Groovy language. It enables teams to code their task setups and version control them alongside their application code.
• The Pipeline DSL enables teams to define pipeline workflows using Groovy code. This enables teams to develop and reuse pipeline code across different projects by defining their whole pipeline as code, including the build, test, and deployment stages.

41. What is the process for configuring Third-party tools in Jenkins?

Jenkins may be set up to operate with a variety of third-party technologies, including version control systems, build tools, testing frameworks, and deployment tools. Here's a rundown of how to configure third-party tools in Jenkins:

• Most third-party programs necessitate the installation of a Jenkins plugin. Navigate to the Jenkins Plugin Manager and look for the plugin you require. Install and configure the plugin in accordance with the instructions.
• Configure the tool in Jenkins once the plugin has been installed. This usually entails supplying connection information, authentication credentials, and other necessary settings.
• Once the tool has been configured, test it to check that Jenkins can connect with it and that it is functioning properly. This could be running a test build or issuing a simple command.
• Integrate the tool into Jenkins jobs once it has been configured and tested. Adding build phases, post-build activities, or triggers that use the tool to do specific tasks may be involved.
• Keep an eye on the tool's performance and troubleshoot any problems that develop. This could include going over logs, modifying configuration settings, or updating plugins.

42. What are some of the default environmental variables in Jenkins?

By default, Jenkins creates various environment variables that can be used in build phases, scripts, and plugins. Some of the most frequent Jenkins default environment variables are

• BUILD_ID
• BUILD_NUMBER
• BUILD_TAG
• BUILD_URL
• EXECUTOR_NUMBER
• JOB_NAME
• NODE_LABELS
• NODE_NAME
• WORKSPACE
• GIT_COMMIT
• GIT_BRANCH
• GIT_URL

43. What are some of the Jenkins pipeline's important components?

Here are some critical aspects of the Jenkins pipeline:

• Pipeline script: The pipeline script defines the pipeline's stages, steps, and conditions. It can be authored in Scripted or Declarative syntax and is commonly stored in the project repository as a Jenkinsfile.
• Stages: The pipeline is separated into stages that correspond to different stages of the construction process, such as building, testing, and deploying. Each stage can have many steps that are carried out progressively.
• Steps: Individual actions performed within a stage, like running a command, executing a script, or starting a build, are referred to as steps.
• Conditions: To govern the pipeline flow, conditions can be defined within the pipeline script. For example, if a test fails, the pipeline can be configured to either abort or proceed to the next stage.
• Integration with other tools: Jenkins pipelines can be integrated with a variety of tools, including version control systems, build tools, testing frameworks, and deployment tools.

44. How to deploy a custom build of a core plugin?

To deploy a custom build of a core plugin in Jenkins, follow these steps:

• To begin, obtain the source code for the plugin you wish to modify from the Jenkins GitHub repository.
• Change or customize the source code as needed to implement the desired changes or adaptations.
• Run the Maven command mvn package in the plugin source code directory to build the changed plugin. This will generate a.hpi file in the specified directory.
• Turn off the Jenkins service.
• Transfer the .hpi file to $JENKINS_HOME/plugins.
• After that, delete the plugin's development directory.
• Next, make a new file called <plugin> .hpi.pinned
• Finally, restart Jenkins and use your modified core plugin build.

Advanced Jenkins interview Questions

45. What are the three security techniques Jenkins employs for user authentication?

Jenkins supports a variety of user authentication mechanisms, and the specific approaches used may vary depending on the system configuration. However, here are three typical security mechanisms for user authentication that Jenkins can employ:

• Jenkins internal user database: Jenkins features an internal user database that holds user credentials in encrypted form, including usernames and passwords. Users can create accounts in Jenkins and log in with credentials saved in this database.
• LDAP (Lightweight Directory Access Protocol) authentication: Jenkins can authenticate users against an LDAP (Lightweight Directory Access Protocol) server. LDAP is a protocol that allows you to access and manage dispersed directory information services via an IP network. Jenkins can handle user accounts and access control using an organization's existing user directory using LDAP authentication.
• Single Sign-On (SSO): To authenticate users, Jenkins can interact with external SSO providers such as SAML (Security Assertion Markup Language) or OAuth. Users can log in once and access numerous systems and applications without having to authenticate in each time. Using SSO, Jenkins can improve security and user experience by delegating user authentication to an external source.

46. What is the use of the JENKINS_HOME directory?

After installation, Jenkins creates the JENKINS_HOME directory and serves as the default destination for all configuration files, plugins, logs, and other relevant data.

Here are some of the most important applications of the JENKINS_HOME directory:

• Storage of configuration files: The JENKINS_HOME directory holds Jenkins configuration files, such as Jenkins server settings, installed plugins, and other system-wide information.
• Storage of data: The JENKINS_HOME directory is also used to store data generated by Jenkins during its operation, such as build artifacts, logs, and build histories.
• Backup and restore: Because the JENKINS_HOME directory contains all of the key data and configuration files, it is critical to back up this directory frequently. A backup of the JENKINS_HOME directory can be used to restore Jenkins to its prior condition in the event of a system failure.

47. Explain a backup plugin and its uses

A backup plugin allows you to back up the Jenkins home directory, which contains all of the crucial configuration data, plugins, logs, and other important files. Here are some important use cases of it:

• Disaster recovery: Jenkins administrators can use the backup plugin to create regular backups of the Jenkins home directory, which can be used to restore the complete Jenkins instance in the event of a disaster or system failure.
• Management of configuration data: The backup plugin makes managing and saving configuration data simple, ensuring that all vital data is backed up and secured.
• Version control: By backing up the Jenkins home directory, administrators may save a version history of configuration files and other vital data.
• Testing and staging: Administrators can use the backup plugin to create a backup of the production Jenkins instance and restore it to a staging or testing environment for testing and debugging.

48. How is code coverage measured/tracked using Jenkins in a CI setup?

Using language-specific code coverage plugins such as JaCoCo, CodeCov, and others, or general tools/plugins such as Sonarqube, which will add code coverage data to builds with minor code changes and display it as a graph in Jenkins.

49. What is Jenkins Remote Access API?

Jenkins Remote Access API is a RESTful web service provided by Jenkins that allows external applications to interface with Jenkins programmatically.

The Remote Access API exposes a collection of HTTP endpoints that accept HTTP GET, POST, PUT, and DELETE requests, including query parameters and/or JSON payloads. The API produces JSON-encoded replies with the required data or status codes indicating whether the requested action was successful or unsuccessful.

50. Can we use conventional Observability tools to monitor Jenkins?

We may use typical observability technologies like Prometheus, Grafana, and ELK Stack, JavaMelody to monitor Jenkins.

Along with these technologies, Jenkins plugins can export data to external monitoring and alerting systems like Datadog, New Relic, or Splunk. These plugins allow you to deliver metrics, logs, and events in a format compatible with these services' APIs.

51. Explain Ping Thread in Jenkins and how it works.

The Jenkins Ping Thread is a background thread that checks the Jenkins instance's connectivity with its agents and nodes regularly.

When a Jenkins agent or node is configured, Jenkins sends a ping message to confirm that the agent or node is still connected and available. The ping message contains a unique ID that is connected with the Jenkins-agent/node connection. It also maintains a list of all active connections between Jenkins and its agent/nodes and updates the status according to the response ping message.

The ping Thread sends a ping message every 15 seconds and expects a response within 10 seconds. However, you can change the frequency of ping messages and the timeout period for receiving a response.

52. What do you do when you see a broken build for your project in Jenkins?

If there is a broken build in our project, we can take certain immediate action to resolve it:

• Examine the build console output to determine what went wrong. Determine whether any error messages or stack traces indicate the cause of the build failure.
• Fix the problem once we have identified the source of the build failure. This could entail changing the code, configuration, or build process.
• Rebuild the failed job after resolving the issue to ensure the build is successful. And notify the team.
• Additionally we can add automated tests, perform code reviews, and use static code analysis tools to prevent such failures in the future.

53. How to run automated tests on Jenkins?

You can run automated tests on Jenkins by following these steps:

• Establish your testing framework: Configure a testing framework, such as JUnit, TestNG, or Selenium, to run your automated tests.
• Make a new Jenkins job as follows: Create a new Jenkins job by selecting 'Freestyle project' or 'Pipeline' from the Jenkins dashboard's 'New Item' menu.
• ,Configure the job: Set up the job to run your automated tests. Build steps can be added to install any required dependencies, build your application, and run your tests. You can also configure post-build actions based on test results to send notifications or trigger other jobs.

If your automated tests are part of a larger codebase, you may need to include source code management in the job. You can accomplish this by configuring the job to pull code from a version control system like Git, SVN, or Mercurial.

• Plan the work: Schedule the job to run at regular intervals or manually trigger it using the Jenkins dashboard's 'Build Now' button.
• View test results: Once the job is finished, go to the Jenkins dashboard and look at the test results. You can analyze and visualize your test results using plugins such as the Test Results Analyzer.

54. What are some best practices for using Jenkins in a production environment?

Yes, we can follow several best practices while using Jenkins to make execution bugless with less effort. Here are some of those:

• Use a dedicated Jenkins server: For production For production environments, it is critical to use a dedicated Jenkins server to ensure that the server is not impacted by other applications or processes running on the same machine.
• Secure the Jenkins server: Use strong passwords, enable two-factor authentication, and restrict access to only authorized personnel to ensure that the Jenkins server is properly secured.
• Use version control: Keep all Jenkins configuration files, scripts, and code under version control to track changes and roll back if necessary.
• Use automated backups: Create automated backups of the Jenkins server and the data it stores to ensure that data is not lost in the event of a failure or disaster.
• Monitor performance: Monitor the performance of the Jenkins server and the builds that run on it to identify and resolve any issues that may arise.
• Distributed builds: Distributed builds distribute a load of running builds across multiple machines, reducing the load on the Jenkins server and improving overall building efficiency.
• Automated testing: Automated testing ensures that builds are functional and meet project requirements. Unit tests, integration tests, and acceptance tests are examples of this.

Note : Check out our blog for Jenkins best practices for better CI performance

Conclusion

Jenkins is a well-known and powerful tool for continuous integration and delivery. To successfully implement Jenkins in a production environment, you must first understand its features and capabilities, as well as best practices for using it.

It is essential to have clarity about the core concepts of Jenkins to clear the interview. Knowing how to install and configure Jenkins, create pipelines and jobs, use agents and plugins, secure the server, monitor performance, and integrate with other tools and services are all part of this. Candidates can demonstrate their knowledge and expertise in this area by being prepared to answer the most frequently asked Jenkins interview questions, increasing their chances of securing a position that requires Jenkins skills.