Day 29: Jenkins Important Interview Questions

9 min readJul 16, 2023

Welcome to Day 29 of our comprehensive series on Jenkins interview questions! In today’s edition, we dive into the world of Jenkins, a powerful and widely-used open-source automation server that has revolutionized the way software development teams approach continuous integration and continuous delivery (CI/CD).

Here are some Jenkins-specific questions related to Docker that one can use during a DevOps Engineer interview:

1. What’s the difference between continuous integration, continuous delivery, and continuous deployment?

Continuous integration:

Developers practicing continuous integration merge their changes back to the main branch as often as possible. The developer’s changes are validated by creating a build and running automated tests against the build. By doing so, you avoid integration challenges that can happen when waiting for release day to merge changes into the release branch.

Continuous Delivery :

Continuous Delivery is an extension of Continuous Integration that takes the process a step further. After successful integration and automated testing in the CI stage, the code is continuously delivered to a staging environment. In this environment, it undergoes further testing, including user acceptance testing, performance testing, and security testing. The entire delivery process is automated, ensuring that the application is always in a deployable state. The key distinction between Continuous Delivery and Continuous Deployment lies in the deployment to production — while in Continuous Delivery, the decision to deploy to production is still manual, in Continuous Deployment, the process is fully automated (more on this below).

Continuous Deployment :

Continuous Deployment takes the concept of Continuous Delivery to its ultimate form by automating the deployment of code changes directly to production once they pass all the necessary tests. In other words, as soon as new code is successfully tested in the staging environment, it is automatically released to the production environment without any manual intervention. This approach ensures that the latest and most thoroughly-tested version of the software is always available to end-users.

2. What is meant by CI-CD?

CI/CD stands for Continuous Integration and Continuous Delivery/Continuous Deployment. It is a set of practices that automate the process of building, testing, and deploying code changes, leading to faster and more reliable software development and releases.

. What are Benefits of CI/CD?

Improved quality: CI-CD can help to improve the quality of software by catching errors early and preventing them from being introduced into the codebase.
Increased speed: CI-CD can help to increase the speed of software delivery by automating the build, test, and deployment process.
Reduced risk: CI-CD can help to reduce the risk of releasing buggy software by automating the testing process and deploying software to a staging environment before deploying it to production.
Increased transparency: CI-CD can help to increase transparency in the software development process by making it easy to see what changes have been made to the codebase and when they were made.
Improved collaboration: CI-CD can help to improve collaboration between developers by making it easy to share code and track changes.

4. What is Jenkins Pipeline?

Jenkins Pipeline is a suite of plugins that allows you to define and automate your build, test, and deployment workflows as code in Jenkins using a script-like syntax.

There are two types of Jenkins Pipeline:

1.Declarative Pipeline: It uses a structured, more opinionated syntax, making it easier to write and read, especially for users who are new to Jenkins Pipeline. Declarative Pipeline abstracts the underlying implementation details and focuses on defining the desired state of the CI/CD process.

2. Scripted Pipeline: It uses a more flexible, script-like syntax, providing more control over the build process with a fine-grained level of customization. While powerful, Scripted Pipeline requires more expertise in Jenkins and Groovy scripting.

This approach enables continuous integration and delivery by automating the entire software development process.

5. How do you configure the job in Jenkins?

To configure a job in Jenkins:

Go to Jenkins > Create a new job and choose its type.
Set general options, like a job description and parameters.
Configure source code management (if using version control).
Choose build triggers (manual, scheduled, or based on code changes).
Define build steps for compiling, testing, and packaging code.
Add post-build actions, such as archiving artifacts or notifications.
Save the configuration and trigger the build manually or automatically based on the chosen triggers.

6. Where do you find errors in Jenkins?

In Jenkins, you can find errors in:

Console Output: Real-time logs during a job run.
Build History: Previous build statuses and error details.
Jenkins Logs: Located in the server’s file system.
Email Notifications: Error messages sent via email.
System Configuration: Check the “System Log” and “Manage Plugins” pages.
Pipeline Syntax: Validate and check for errors in pipeline scripts.
Plugin Logs: Examine logs for specific plugin-related issues.
Jenkins User Interface: Look for warning and error icons in the dashboard and configurations.

7. In Jenkins how can you find log files?

In Jenkins, log files can be found in the Jenkins server’s file system. The location of these log files may vary depending on the installation method and the operating system on which Jenkins is running. Here are the general steps to find log files in Jenkins:

Jenkins Home Directory: The main directory where Jenkins stores its configuration and data is known as the Jenkins home directory. You need to locate this directory first.
Log Directory: Within the Jenkins home directory, there is typically a subdirectory specifically designated for log files. This directory is often named “logs” or “log.”
Log Files: Inside the log directory, you will find various log files, each serving a different purpose. Common log files include “jenkins.log,” which contains the main Jenkins server log, and “error.log,” which captures error messages.
Accessing Log Files: You can access the log files using standard file system navigation tools. On Linux-based systems, you can use the “cd” command to navigate to the Jenkins home directory and then to the logs directory. On Windows, you can use the file explorer to locate the Jenkins home directory and navigate to the logs directory.

8. Jenkins workflow and write a script for this workflow?

Jenkins Workflow, also known as Jenkins Pipeline, is a way to define your software delivery process using code. It allows you to create complex, continuous delivery pipelines as code, providing better traceability, versioning, and maintainability. A Jenkins Pipeline can be written in either Declarative or Scripted syntax.

Here’s a simple example of a Jenkins Declarative Pipeline script that demonstrates a basic workflow:

pipeline {
    agent any    
      stages {
        stage('Build') {
            steps {
                echo 'Building the application...'
                // Add actual build steps here
            }
        }
        stage('Test') {
            steps {
                echo 'Running tests...'
                // Add actual test steps here
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying the application...'
                // Add actual deployment steps here
            }
        }
    }

9. How to create continuous deployment in Jenkins?

To create continuous deployment in Jenkins:

Set up a Jenkins Pipeline job.
Integrate with version control (e.g., Git).
Define build, test, and deployment stages.
Deploy to staging after successful testing.
Optionally, include user acceptance testing.
Automate deployment to production.
Implement post-build actions and security measures.
Monitor and iterate for continuous improvement.

10. Is Only Jenkins enough for automation?

No, it is not the only tool used for automation, like CircleCI, Jenkins X, Ansible, Chef, Puppet, TeamCity, etc.

11. How will you handle secrets?

There are many ways:

Using Jenkins Credentials Plugin.
Using a third-party plugin like Vault

12. Name some of the plugins in Jenkin?

Jenkins has a vast ecosystem of plugins that extend its functionality and enable integration with various tools and technologies. Here are some popular Jenkins plugins:

Git Plugin: Integrates Jenkins with Git version control system, allowing Jenkins to pull code from Git repositories.
GitHub Integration Plugin: Provides integration with GitHub, enabling Jenkins to automatically build projects when changes are pushed to GitHub repositories.
Pipeline Plugin: Offers support for defining continuous delivery pipelines as code using Jenkins Pipeline DSL.
Build Pipeline Plugin: Visualizes and manages complex build workflows in a graphical manner.
Credentials Plugin: Enables secure management and storage of usernames, passwords, and other sensitive data.

13. What is Groovy in Jenkins?

Apache Groovy is a dynamic object-oriented programming language used as a scripting language for Java platforms.
Groovy is used to orchestrate the Jenkins pipeline and enables different teams to contribute to the work in different languages.
Groovy’s syntax is very similar to that of Java, making it more seamless with the Java interface.
The language has several features like Java compatibility and Development support.

14. How can you create a backup and copy files in Jenkins?

Jenkins stores all the settings, builds scripts, and logs in the home directory.
Then, if you want to create a backup of this Jenkins set up all you have to do is copy this directory.
The job directory may also be copied to clone a job or rename the directory.

15. What is Jenkinsfile?

Jenkins file is a text file that has a definition of a Jenkins pipeline and is checked into the source control repository. It enables code review and iteration on the pipeline. It also permits an audit trail for the pipeline.

16. Explain the ways to configure Jenkins node agent to communicate with Jenkins master?

There are two ways to configure Jenkins node agent to communicate with Jenkins master:

Browser–If we launch the Jenkins node agent from a browser, a Java Web Start or JNLP file is downloaded. The downloaded file launches a new process on the client machine to run jobs.
Command-line–If you want to start the node agent using the command line, you need the executable agent.jar file. When this file runs, it launches a client’s process to communicate with the Jenkins master to run build jobs.

17. What are the three security mechanisms Jenkins uses to authenticate users?

The three mechanisms are as follows:

Jenkins uses an internal database to store user data and credentials.
Jenkins can use a lightweight Directory Access Protocol (LDAP) server to authenticate users.
We can configure Jenkins to employ the application server’s authentication mechanism upon which we deploy it.

18. How to change port for Jenkins?

Jenkins, by default, runs on port number 8080. For changing the existing port from 8080 to the desired port number, we can take the following steps:

Run Jenkins using the command line
Execute the command, java -jar -httpPort=desired_port jenkins.war

If Jenkins is installed using the Windows package, then:

Go to Program Files/Jenkins directory
Open Jenkins.xml in the editor

Find –httpPort=8080 and replace the port 8080 with the new port number

19. Mention what are the two components Jenkins is mainly integrated with?

Jenkin is mainly integrated with two components:

Version Control system like GIT, SVN
And build tools like Apache Maven.

20. There is a broken build in your Jenkins project, then what will you do?

First, we need to open the console output where the broken build is created and then see if there are any file changes that were missed. If we do not find any issues in this manner, then we can update our local workspace and replicate the problem and then try to solve it.

21. From one server to another, how do you copy or move your Jenkins jobs?

First, we need to copy our jobs directory from the old to the new server. There are multiple ways to do it. We can either move the job from the installation by simply copying the corresponding job directory or we can make a clone of the job directory by making an existing job’s copy. For this, we need to have a different name, which we can rename later.

In conclusion, Jenkins has become an indispensable tool in modern software development and DevOps practices. As we wrap up our exploration of “Day 29: Jenkins Important Interview Questions,” we have delved into various fundamental concepts surrounding Jenkins, Continuous Integration (CI), Continuous Delivery (CD), and Continuous Deployment (CD).

Practice the Jenkins more and refer to this article before giving your interviews. Happy learning!!!