Interview Questions on Jenkins
1. What is Jenkins?
Jenkins is a self-contained, open-source automation server that can be used to automate all sorts of tasks related to building, testing, and delivering or deploying software. Jenkins can be installed through native system packages, Docker, or even run standalone by any machine with a Java Runtime Environment (JRE) installed.
2. What is continuous integration in Jenkins?
In software development, multiple developers or teams work on different segments of the same web application so you have to perform integration test by integrating all modules. In order to do that an automated process for each piece of code is performed on daily basis so that all your codes get tested. This process is known as continuous integration.
3. What is the requirement for using Jenkins?
For using Jenkins, you have to need a source code repository that is accessible. For example, a Git repository and a working build script, e.g., a Maven script, checked into the repository.
4. What are the advantages of Jenkins?
Advantage of Jenkins includes:
1) Bugs tracking is easy at an early stage in the development environment.
2) Provides large numbers of plugin support.
3) Iterative improvement to the code.
4) Build failures are cached at the integration stage.
5) For each code commit changes an automatic build report notification generates.
6) To notify developers about build report success or failure, it is integrated with the LDAP mail server.
7) Achieves continuous integration agile development and test-driven development.
8) With simple steps, the maven release project is automated.
5. How can you clone a Git repository via Jenkins?
If you want to clone a Git repository via Jenkins, you have to enter the e-mail and user name for your Jenkins system. Switch into your job directory and execute the "git config" command for that.
6. How can you set up Jenkins jobs?
1) Select the new item from the menu.
2) After that enter a name for the job and select a freestyle job.
3) Then click OK to create a new job in Jenkins.
4) The next page enables you to configure your job.
7. What are the two components Jenkins is mainly integrated with?
1) Version Control systems like GIT, SVN
2) And build tools like Apache Maven.
8. What is a Jenkins job?
A Job/Project is the fundamental unit of a logical work (like a software build, an automation task, test execution, etc) using the Jenkins automation server and other required plugins, configurations & infrastructures.
Jobs can be of different types like - a freestyle project, a multi-configuration project, a pipeline project, a multi-branch project, etc.
9. What is a Jenkins Pipeline?
The pipeline is a special type of Jenkins job - simply a sequence of steps controlled by a defined logic - which Orchestrates long-running activities that can span across multiple build agents. It is suitable for building pipelines (formerly known as workflows) and/or organizing complex activities that cannot be easily achieved using a freestyle job.
10. What are the types of Jenkins pipelines?
Jenkins Pipelines can be either - a Declarative pipeline or a Scripted Pipeline. Declarative pipeline makes use of numerous, generic, predefined build steps/stages (i.e. code snippets) to build our job according to our build/automation needs whereas, with Scripted pipelines, the steps/stages can be custom-defined & used using a groovy syntax which provides better control & fine-tuned execution levels.
11. How do you store credentials in Jenkins securely?
Credentials can be stored securely in Jenkins using the Credentials plugin, which stores different types of credentials like - 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 and when required.
12. What is Jenkins Build Cause?
Build Cause is a text attribute that represents what made a job's build to be triggered, say it could be a Jenkins User (from UI), Timer for Scheduled jobs, Upstream jobs for a job which was triggered by upstream job, etc. This is mainly used to identify the nature of the builds - be it nightly, manual, automated, etc.
13. How Jenkins knows when to execute a Scheduled job/pipeline and how it is triggered?
Jenkins master will have the cron entries set up for the jobs as per the scheduled Job's configurations. As and when the time for a particular job comes, it commands agents (based on the configuration of the job) to execute the job with the required configurations.
14. What are the Scopes of Jenkins Credentials?
Jenkins credentials can be of one of the two scopes - Global & System
1) 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)
2) 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.
15. How to do Global Tools Configuration in Jenkins?
Global Tools are tools that need to be installed outside the Jenkins environment and need to be controlled from within the Jenkins environment. Hence it needs its corresponding Jenkins plugin as well. Steps to using a Global Tool generally include -
1) Install the tool Plugin into the Jenkins instance, to include the global tool into a list of global tools used by Jenkins.
2) Install the tool in the Jenkins instance or provide away (maybe a command to download and) install the tool during runtime.
3) Go to Manage Jenkins -> Global Tools Configuration and Scroll through the tool list and configure the global tool-specific configurations.
4) Make use of the installed global Tool in your job/pipeline.
16. How code coverage is measured/tracked using Jenkins in a CI environment?
Using language-specific code coverage plugins like JaCoCo, CodeCov, etc or generic tools/plugins like Sonarqube which will add the code coverage data to builds with some minor tweaks in the code and the same can be displayed as a graph in Jenkins.
17. What is the Jenkins User Content service?
Jenkins has a mechanism known as "User Content", where administrators can place files inside the $JENKINS_HOME/userContent folder and these files are served from yourhost/jenkins/userContent.
This can be thought of as a mini HTTP server to serve images, stylesheets, and other static resources that you can use from various description fields inside Jenkins.
18. What is a Jenkins Shared Library and how it is useful?
As an organization starts using more and more pipeline jobs, there is a chance for more and more code being duplicated in every pipeline job, since a part of the build/automation processes will be the same for most of the jobs. In such a situation, every other new upcoming job should also duplicate the same piece of code. To avoid duplications, the Jenkins project brought in the concept of Shared Libraries, to code - DRY - Don't Repeat Yourself.
Shared libraries are a set of code that can be common for more than one pipeline job and can be maintained separately. Such libraries improve the maintenance, modularity & readability of the pipeline code. And it also speeds up the automation for new jobs.
19. What happens when a Jenkins agent is offline and what is the best practice in that situation?
When a job is tied to a specific agent on a specific node, the job can only be run on that agent and no other agents can fulfill the job request. If the target node is offline or all the agents on that particular node are busy building other jobs, then the triggered job has to wait until the node comes online or an agent from that node becomes available to execute the triggered build request.
As a result, a triggered job may sometimes wait indefinitely without knowing that the target node is offline. So, it is always the best practice to tie the jobs to a group of nodes & agents, referred to with a 'Label'. Once a job is tied to a Label, instead of a specific node/agent, any of the nodes/agents falling under the label can fulfill a build request, when a job is triggered. This way we can reduce the overall turn-around time of the builds.
Even then if a job is waiting for more time for the nodes/agents, then it is time to consider adding more nodes/agents.
20. What is the Blue Ocean?
Blue Ocean is the redefined user experience for Jenkins. Designed from the ground up for Jenkins Pipeline, it is still compatible with freestyle jobs, Blue Ocean reduces clutter and increases clarity. Blue Ocean’s main features include -
1) Sophisticated visualizations of continuous delivery (CD) Pipelines, allowing for fast and intuitive comprehension of your Pipeline’s status.
2) Pipeline editor - makes the creation of Pipelines approachable by guiding the user through an intuitive and visual process to create a Pipeline.
3) Personalization to suit the role-based needs of each member of the team.
4) Pinpoint precision when intervention is needed and/or issues arise. Blue Ocean shows where in the pipeline attention is needed, facilitating exception handling and increasing productivity.
5) Native integration for branch and pull requests, enables maximum developer productivity when collaborating on code with others in GitHub, Bitbucket, etc.
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