10 Basic Jenkins Interview Questions and Answers

Jenkins is a widely used online server or tool for CI/CD project development. It is gaining more popularity day by day as it helps you to enhance code quality and the speed of development with simple automation. 

Here are some common Jenkins interview questions along with their answers. These are very common questions asked in interviews to experienced developers and DevOps engineers. Don’t appear for the interview if you don’t know the answers to these basic questions.

Let’s begin.

1. What is Jenkins? What is the primary use of Jenkins in software development?

Answer:

Jenkins is an open-source automation server. It is used for Continuous Integration (CI) and Continuous Delivery (CD) in software development. With Jenkins, you can automate various aspects of the software development lifecycle, starting from the building, testing, and then deploying applications.

2. How does Jenkins facilitate the CI/CD process?

Answer:

Jenkins facilitates CI/CD by automating the following key tasks:

• Fetching code from source control repositories (like GitLab, and GitHub…) and making executable build.
• Running automated tests on the build to verify the features and code quality of the project.
• Packaging and deploying applications to different environments. It ensures that the project works in different environments seamlessly.
• Monitoring and reporting on the status of builds and deployments, so that any failure can be fixed immediately.
• Triggering builds and deployments automatically based on code changes. When you push new changes to the repository, Jenkins triggers the build for testing.

These are the basic tasks offered by Jenkins. There are many more tasks you can accomplish as per your project demand using the Jenkins server.

3. What is the architecture Jenkins server follows? Explain.

Answer: The Jenkins server is based on the Master-Slave architecture. 

As we all know, the main purpose of the Master-Slave setup is to distribute the workload across multiple nodes so that a larger number of jobs can be concurrently run. It also enables running jobs on different platforms or environments with different configurations.

Here, the master is the main Jenkins server. It is responsible for managing jobs and distributing them to slave nodes. Slave nodes are nothing but the additional Jenkins servers or agents responsible for executing the build and testing jobs. 

4. How do you create a Jenkins job (or project)? Explain the steps.

Answer: 

You just have to follow the simple steps to create a Jenkins job.

• Log in to the Jenkins dashboard with your credentials.
• Click on “New Item.” (Make sure you have permission to create a new Jenkins job).
• Enter a name for the job. Select the desired job type (e.g., Freestyle project or Pipeline).
• Configure the basic job details such as build steps, source code repositories link, and post-build actions.
• Save the job configuration.

That’s all you have to do. Oh, you have created your first Jenkins job!

5. How do you trigger a build manually, and how can builds be scheduled automatically?

Answer: 

In Jenkins, we can trigger the builds manually or automatically or you can even schedule them. 

To trigger a build manually, log in to your Jenkins dashboard. You will see the “Build Now” button for the specific job. Click on it. 

To schedule builds automatically, you have to use the “Build Triggers” section in the job configuration. You can configure to execute Jenkins build at a specific time or after a certain time interval.

You can also configure the job to execute the build whenever new code is pushed to the code repository. (This use case is very useful and mostly used to identify the flaws in the code immediately after pushing new code.)

6. What are Jenkins pipelines? Why do we use them for defining complex build and deployment processes?

Answer: 

First of all, Jenkins pipelines are a way to define and automate complex CI/CD processes using code. 

Jenkins pipelines are defined in a Jenkinsfile, which can be versioned along with the application code. 

The benefits of the Jenkins Pipelines are: 

• They provide better visibility, traceability, and reusability of build and deployment processes. 
• They also allow for easy integration with version control systems (such as git). 
• Pipelines can be easily shared across teams to create new Jenkins pipelines with minimal or no changes.

7. What is a Jenkinsfile? What is the use of it in Jenkins Pipeline?

Answer:

A Jenkinsfile is a text file that can be opened in any text editor written in a human-readable format. You can use Jenkinsfile to define the steps of a Jenkins Pipeline. 

You can define the entire CI/CD process by writing code in Jenkinsfile. This file is versionable and reproducible to reuse for other job creation. 

Jenkinsfiles are especially useful in Jenkins Pipeline projects because they provide a structured way to define and manage complex build and deployment workflows.

8. How can you secure a Jenkins installation? Describe best practices for Jenkins security.

Answer:

Jenkins has access to your project code repository. Securing your Jenkins job should be your up-most priority.

Here are some of the best practices you should follow to secure a Jenkins installation.

• As we use for other authentication, use strong authentication methods, such as LDAP or Active Directory.
• Setup role-based access control (RBAC) to provide necessary permissions only for each user.
• Keep your Jenkins and its plugins up-to-date. A new patch usually mitigates the known security vulnerabilities.
• Limit physical access to Jenkins servers so that none of your data gets compromised.
• Keep monitoring the logs. Set up alerts for any suspicious activities.
• Disable or delete any unused features and plugins.

9. How can Jenkins be integrated with Docker for building and deploying containerized applications?

Answer: 

(For integration, you have to get familiar with the useful docker commands.)

Jenkins can be integrated with Docker, for that you need Docker agents.

What are Docker agents?

Docker agents are Jenkins nodes that are responsible for running Docker containers. With the docker containers, Jenkins can build, test, and deploy the applications within isolated containers. 

There are many Docker plugins available for managing Docker images and containers within Jenkins pipelines.

10. How do you handle exceptions in PowerShell scripts?

Answer: 

You can write the In PowerShell script to run inside the Jenkins job. To avoid interruption to the Jenkins job from any exception, you have to handle the exception gracefully.  You can handle exceptions using a try...catch block. Here is a syntax and a PowerShell code example:

try {
	# Code that might throw an exception 
	$result = 10 / 0 
} catch { 
	# Handle the exception 
    Write-Host "An exception occurred: $_" 
}

In this example, if an exception occurs during the division operation, it will be caught in the catch-block, allowing you to handle it gracefully.

I hope you find these Jenkins questions useful for your job interview preparation. If you have any doubts or questions to ask, write in the comment section below. All the best!

Aniruddha Chaudhari

I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.