Introduction
Jenkins is a leading open-source automation server that provides hundreds of plugins to support building, deploying, and automating software projects. If you’re looking to land a DevOps job or any role that involves continuous integration, it’s crucial to prepare for Jenkins interview questions. Here are 50 of the most common Jenkins interview questions and their answers.
1. What is Jenkins?
Jenkins is an open-source continuous integration tool written in Java. It automates the non-human part of the software development process, with continuous integration and facilitating technical aspects of continuous delivery.
2. What are the advantages of using Jenkins?
Jenkins helps to automate several parts of the software development process, which includes code deployment to different environments, code testing, building the project, and others. It’s easy to set up, has a vast plugin ecosystem, and supports distributed builds.
3. What is continuous integration in Jenkins?
Continuous Integration (CI) in Jenkins involves the continuous building and testing of code every time a team member commits changes to version control. CI helps to detect errors as quickly as possible.
4. What is a Jenkins Pipeline?
Jenkins Pipeline is a set of plugins that supports implementing and integrating continuous delivery pipelines into Jenkins. A pipeline has an extensible automation server for creating simple or complex delivery pipelines “as code” via the Pipeline DSL.
5. How do you create a Jenkins Pipeline?
You can create a Jenkins pipeline by writing a Jenkinsfile, which is a text file that contains the definitions for a Jenkins Pipeline and checks into the source control repository.
6. What is a Jenkinsfile?
Jenkinsfile is a text file that contains the definition of a Jenkins Pipeline and is checked into a project’s source control repository. It allows you to define an entire continuous delivery pipeline.
7. What is a master and agent in Jenkins?
In Jenkins, a master represents the machine or system where Jenkins runs. An agent is a computer set up to offload build projects from the master.
8. What is a build in Jenkins?
A build in Jenkins is a process where source code (from a version control system) is fetched, compiled, and packaged into a deployable format like JAR, WAR, or Docker Image.
9. What is the difference between a freestyle build job and a pipeline job in Jenkins?
A freestyle build job is a flexible and very configurable option, and it’s rather GUI based. On the other hand, a pipeline job allows you to manage multiple complex jobs with the help of pipeline scripts in the Jenkinsfile in your source code repository.
10. What is SCM in Jenkins?
Source Code Management (SCM), like Git, SVN, etc., is used by Jenkins to automate the build and test process. Jenkins contains a built-in SCM module to communicate with different repositories.
11. What is Groovy in Jenkins?
Groovy is the default scripting language used for the Jenkins DSL (Domain-Specific Language). It’s used to write scripts for Jenkins.
12. How to schedule a job in Jenkins?
A job can be scheduled in Jenkins by using the “Build periodically” field in the build triggers section of the job configuration. Jenkins uses the syntax of UNIX cron, with some minor differences.
13. What are the different types of Jenkins jobs?
The different types of Jenkins jobs include Freestyle projects, Pipeline, Maven, Multi-configuration projects (Matrix projects), and External projects.
14. What is a trigger in Jenkins?
A trigger in Jenkins decides when to run the job. It can be triggered manually or automatically, such as when code is committed to a repository, or at a specified time or interval.
15. What is a Jenkins Plugin?
A Jenkins plugin is a tool that enhances the functionality of Jenkins. It’s a way to extend Jenkins and integrate it with other software tools. There are hundreds of Jenkins plugins available.
16. Can you name some commonly used plugins in Jenkins?
Some commonly used plugins in Jenkins are Git, Maven 2 project, Amazon EC2, HTML publisher, Green Balls, Join, Build Pipeline Plugin, etc.
17. What is a build step in Jenkins?
A build step in Jenkins is a task that needs to be executed. For example, invoking a shell script, running a Windows batch command, running Ant, running Maven, etc.
18. How to secure Jenkins?
Jenkins can be secured using various ways including:
- Ensuring global security is on.
- Securing the Jenkins user interface with an authentication mechanism.
- Authorizing matrix-based security.
- Setting up secure HTTP, using a reverse proxy, or even setting up a firewall.
19. What is Jenkins CLI?
Jenkins CLI (Command Line Interface) is a means to interact with Jenkins from a script or from your shell. This is convenient for automation of routine tasks, bulk updates, troubleshooting, and more.
20. How do you back up Jenkins?
Jenkins can be backed up by periodically backing up JENKINS_HOME directory onto a separate hard disk or into a cloud storage system. Also, there are backup plugins available such as thinBackup.
21. How can you clone a Git repository via Jenkins?
Jenkins can clone a Git repository by using the Git plugin. In the job configuration, go to “Source Code Management” –> “Git” then enter the Repository URL.
22. What are the parameters in Jenkins?
Parameters in Jenkins are supported “parameters” that can be given when manually building Jenkins jobs. These parameters can be text string, a list of choices, a boolean checkbox, a password, etc.
23. What is Jenkins Workspace?
A workspace is a directory where Jenkins builds your projects: it contains the source code of the job’s last build, and all the outputs.
24. How can you deploy a custom build of a core plugin?
To deploy a custom build of a core plugin, you need to clone the source code of the plugin, make changes, build it, remove the original plugin from Jenkins, and install your version.
25. What is Jenkins Artifactory?
Jenkins Artifactory is a binary repository manager for use by build tools (like Maven and Gradle), CI Servers (like Jenkins) and repository browsers (like Artifactory).
26. What is a node in Jenkins?
A node in Jenkins is a machine that is part of Jenkins’ environment and is capable of executing Pipelines or Projects. Jenkins distributes the workload of building projects on different nodes.
27. How can Jenkins be used to automate testing?
Jenkins supports several testing and reporting plugins. Jenkins can execute shell scripts, Windows batch commands, Ant targets, and Maven targets for automated testing.
28. How do you setup and run a Jenkins job?
Firstly, install Jenkins and navigate to your Jenkins dashboard. Choose ‘new item’ on the dashboard to create a job. Configure the job with the necessary steps and save it. Then build it by clicking ‘build now’ on the job page.
29. How do you install a Jenkins plugin?
Navigate to the Manage Jenkins -> Manage Plugins -> Available section. You can search for your desired plugin, select it and then click on Install without restart or Download now and install after restart.
30. How do you add a node in Jenkins?
To add a node in Jenkins, go to Manage Jenkins -> Manage Nodes and Clouds -> New Node. Specify the name of the node, select Permanent Agent, and specify the necessary details.
31. How do you handle secure secrets in Jenkins?
Jenkins has a credentials plugin that stores the secrets in an encrypted form on the controller’s disk and provides a standardized API for storing and retrieving them.
32. What is the role of a Jenkinsfile?
A Jenkinsfile is used to define the pipeline as code and automate the pipeline process. It allows you to script your build pipeline consisting of one or more build jobs into a single workflow.
33. What are scripted and declarative pipelines in Jenkins?
Scripted pipelines are based on Groovy as their Domain-specific language. Declarative pipelines were introduced to offer a simpler and more opinionated syntax for writing Jenkins Pipeline. It has a pre-defined structure.
34. How do you parameterize a Jenkins job?
To parameterize a Jenkins job, enable the “This project is parameterized” option in the job configuration, add parameters of various data types like String, Boolean, Choice, etc., and use them in the job steps as variables.
35. How do you troubleshoot a Jenkins build failure?
You can troubleshoot a Jenkins build failure by checking the console output for any errors or warnings, investigating the logs of the specific Jenkins job, checking the system logs, or even increasing the logging level in the Jenkins system settings.
36. What is distributed build in Jenkins?
Distributed builds in Jenkins are used to distribute the load of building projects on multiple machines. It allows for running jobs on different environments, speeding up the build process, and saving time.
37. What is Jenkins Blue Ocean?
Blue Ocean is a project that rethinks the user experience of Jenkins, modelling and presenting the process of software delivery by surfacing information that’s important to development teams with as few clicks as possible, while still staying true to the extensibility that is core to Jenkins.
38. What is a post-build action in Jenkins?
Post-build actions are operations that are performed after the build steps have been executed. This can be sending email notifications, archiving the build artifacts, triggering other jobs, and more.
39. How do you configure automatic builds in Jenkins?
Automatic builds can be configured by setting up a build trigger in the job configuration. Jenkins can poll SCM for changes, or scripts can use the Jenkins API to trigger builds after a check-in.
40. How can you move or copy Jenkins from one server to another?
Jenkins can be moved by copying the job directory from the old server to the new one. Alternatively, you can also use the “Move/Copy/Promote” Jenkins plugin.
41. How can you ensure that your Jenkins job executes in a specific directory?
You can specify a custom workspace in the job configuration where your Jenkins job will be executed.
42. What are agents in Jenkins?
Agents are essentially Jenkins environments that are set up for distributed builds. They run on different machines that handle the job distributed by the Master.
43. How can you temporarily turn-off Jenkins Security if the administrative users have locked themselves out of the admin console?
If you’ve locked out of Jenkins, you can disable security by editing the Jenkins configuration file ($JENKINS_HOME/config.xml). You need to change the value of the “useSecurity” field from “true” to “false” and then restart Jenkins.
44. How can you speed up Jenkins?
You can speed up Jenkins by distributing the build load to different machines (agents), keeping your system updated with the latest Jenkins version, regularly cleaning up old and unnecessary data, limiting console output, and properly tuning JVM parameters.
45. What is a Jenkins Executor?
A Jenkins executor is a computational resource for compiling your project. Each agent can have one or more executors. You can think of an executor as a single “thread” of building a job.
46. What is a Jenkins Agent and how do you use it?
A Jenkins agent is a machine that is configured to offload build projects from the master. It listens for requests from the Jenkins master instance and runs jobs as directed by the master.
47. How do you use Docker with Jenkins?
Docker can be integrated with Jenkins using the Docker plugin. This allows Jenkins to build and publish images to a Docker registry and to build Docker environments.
48. What is a Matrix project in Jenkins?
A Matrix project is a type of Jenkins job that allows running the same job multiple times in parallel. This is useful for testing your project against different versions of a tool/library or different environments.
49. How do you integrate Git with Jenkins?
Git can be integrated with Jenkins using the Git plugin. This plugin enables Jenkins to fetch the source code from the Git repository and trigger the build whenever a change is pushed to the Git repository.
50. What is Multibranch Pipeline in Jenkins?
A Multibranch Pipeline project type enables you to implement different Jenkinsfiles for different branches of the same project. It automatically creates a new Jenkins job whenever a new branch is discovered in a SCM repository.
Conclusion
Jenkins is a widely used tool, and hence, the demand for professionals with Jenkins skills is high. By preparing these questions, you can significantly increase your chances of cracking your Jenkins job interview. Remember, apart from these questions, understanding the basics of Continuous Integration and Continuous Delivery is also crucial. Happy Learning!