Jenkins Intermediate interview Questions and answers

1. What is grovy in jenkins?

Ans: Groovy is a dynamic programming language that is used in Jenkins to define build workflows and configurations. The Groovy language is a powerful, flexible, and Java-compatible scripting language that is often used in Java environments.

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

Ans: There are several ways to trigger Jenkins jobs or pipelines:

1. Manual Trigger: Jenkins jobs can be triggered manually by clicking the “Build Now” button on the Jenkins web interface.
2. Scheduled Trigger: You can schedule a job to run periodically using the “Build periodically” option in the “Build Triggers” section. This allows you to specify a schedule using cron syntax.
3. SCM Trigger: Jenkins can be configured to detect changes in a version control system (VCS) like Git, SVN, or Mercurial. Whenever there’s a new commit or change in the repository, Jenkins can automatically trigger a build.
4. Trigger by Upstream Projects: A job can be configured to be triggered by the completion of another job. This is useful for setting up a workflow where one job depends on the output of another.
5. Trigger by Remote API: Jenkins provides a remote API that allows you to trigger a build remotely. This can be done using a POST request to the Jenkins server’s /job/job-name/build endpoint, where job-name is the name of the job you want to trigger.
6. Trigger by Webhooks: Many modern VCS providers (e.g., GitHub, GitLab, Bitbucket) support webhooks, which allow them to notify Jenkins whenever there’s a change in the repository. Jenkins can then use this notification to trigger a build.
7. Trigger by Email: Jenkins can be configured to listen for incoming emails and trigger a build based on the content of the email.
8. Trigger by Parameterized Build: Jenkins jobs can be parameterized, allowing you to provide parameters when triggering a build. This can be done manually or via other means like the remote API. 

3. What are the credential types supported by Jenkins?

Ans: Jenkins supports several types of credentials, which can be used to securely store sensitive information such as passwords, SSH private keys, and API tokens. The types of credentials supported by Jenkins include:

1. Username and Password: This type of credential allows you to store a username and password combination. It can be used, for example, to authenticate to an external system.
2. Secret Text: This type of credential allows you to store a secret value, such as an API token or a passphrase.
3. SSH Username with Private Key: This type of credential allows you to store an SSH private key along with the corresponding username. It can be used, for example, to authenticate to a remote server over SSH.
4. Certificate: This type of credential allows you to store an X.509 certificate, which can be used for client authentication.
5. Secret File: This type of credential allows you to store a secret value in a file. The contents of the file will be treated as the credential value.
6. AWS Credentials: This type of credential allows you to store AWS access key ID and secret access key. It can be used, for example, to authenticate to AWS services.

4. What is “Continuous Integration” with reference to Jenkins?

Ans: Continuous Integration (CI) is a software development practice that aims to improve the quality and reliability of software by automating the process of integrating code changes into a shared repository. Jenkins, as a widely used CI tool, plays a key role in implementing CI practices.

5. Name the two components that Jenkins is mostly integrated with?

Ans:

1. Version Control Systems (VCS): Jenkins integrates with various VCS systems such as Git, Subversion (SVN), Mercurial, and Perforce. This integration allows Jenkins to monitor repositories for changes and automatically trigger builds and tests when code changes are detected.
2. Build Tools: Jenkins can be integrated with a wide range of build tools like Apache Maven, Gradle, Ant, and Make. These build tools help Jenkins automate the process of compiling, packaging, and testing code changes.

6. Name some of the useful plugins in Jenkins?

Ans: There are thousands of plugins available for Jenkins, covering a wide range of functionalities. Some of the useful plugins that are commonly used in Jenkins include:

1. Git Plugin: Allows Jenkins to integrate with Git version control systems, enabling automatic builds and tests when code changes are detected.
2. Pipeline Plugin: Enables Jenkins to define continuous integration and continuous delivery pipelines using code (Pipeline as Code).
3. GitHub Integration Plugin: Provides integration with GitHub repositories, enabling Jenkins to automatically trigger builds on GitHub pull requests and branches.
4. Docker Pipeline Plugin: Integrates Jenkins with Docker, allowing Jenkins to run build, test, and deployment processes in Docker containers.
5. Maven Plugin: Integrates Jenkins with Apache Maven, enabling Jenkins to automate Maven-based build and test processes.
6. SonarQube Plugin: Integrates Jenkins with SonarQube, enabling code quality and static analysis checks as part of the CI/CD process.
7. Slack Notification Plugin: Enables Jenkins to send build notifications to Slack channels, allowing teams to stay informed about build statuses.
8. Email Extension Plugin: Extends Jenkins’ email notifications, allowing for more customization and control over email notifications.
9. Artifactory Plugin: Integrates Jenkins with JFrog Artifactory, enabling Jenkins to publish and retrieve build artifacts from Artifactory repositories.
10. Kubernetes Plugin: Integrates Jenkins with Kubernetes, allowing Jenkins to run builds and tests on Kubernetes clusters.
11. Ansible Plugin: Integrates Jenkins with Ansible, enabling Jenkins to automate deployment and configuration management tasks using Ansible playbooks.
12. JIRA Integration Plugin: Provides integration with Atlassian JIRA, enabling Jenkins to create JIRA issues and update issue statuses based on build results.

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

Ans: Jenkins provides several default environment variables that can be accessed within pipelines and other parts of Jenkins:

1. BUILD_ID: The unique identifier for the build.
2. BUILD_NUMBER: The sequential number of the current build.
3. BUILD_TAG: A combination of the job name and the build number.
4. BUILD_URL: The URL of the current build.
5. JENKINS_HOME: The path to the Jenkins home directory.
6. JENKINS_URL: The URL of the Jenkins server.
7. JOB_NAME: The name of the current job.
8. NODE_NAME: The name of the agent where the build is running.
9. WORKSPACE: The path to the workspace directory for the current build.
10. HUDSON_URL: An alias for JENKINS_URL (deprecated).
11. JOB_URL: The URL of the current job.
12. RUN_CHANGES_DISPLAY_URL: The URL of the changes page for the current build.
13. RUN_DISPLAY_URL: The URL of the build result page for the current build.
14. RUN_ID: The ID of the current build.
15. RUN_URL: The URL of the current build.

These variables can be accessed in pipeline scripts using the env object, like this: env.JOB_NAME. They can also be used in other parts of Jenkins, such as in freestyle jobs or shell scripts.

8. How to add users in the jenkins?

Ans: Go to

1. jenkins -> Manage Jenkins -> Users -> click on “Create User”
2. add the below parameters:
   • Username
   • Password
   • confirm password
   • Full Name
   • Email address
3. Click on “Create User”

9.What is continuous integration in Jenkins?

Ans: Continuous integration is the process in which all development work integration is done at the earliest and a code is continuously tested after a commit. This process allows one to discover bugs at an early stage and fix them. The Jenkins build server provides this functionality.

10. How to configure Jenkins with Maven?

Ans:

1. Go to Manage Jenkins -> select Configure System 
2. Scroll down until the Maven section is seen, and then go to Add Maven
3. Uncheck the ‘Install automatically’ box
4. Add any name for the setting and the location of the MAVEN_HOME
5. After saving, one can create a job with the ‘Maven project’ option

11. How to change port for Jenkins?

Ans: Changing the port for Jenkins via the console can be achieved by modifying the Jenkins configuration file. You’ll need to SSH into the server where Jenkins is installed and follow these steps:

1.Locate the Jenkins Configuration File: The Jenkins configuration file is typically located at /var/lib/jenkins/jenkins.xml.

2. Open the jenkins.xml file and Find the HTTP Port Configuration: Within the configuration file, look for the <connector> tag with the port attribute. The default port for Jenkins is 8080. You should see a line similar to this:

sudo vim /var/lib/jenkins/jenkins.xml

<Connector port="8080" ...

3. Change the Port Number: Replace the default port number with the desired port number. For example, to change Jenkins to run on port 8081, modify the line to:

<Connector port="8081" ...

4. Save and Close the File

5. Restart Jenkins:

sudo systemctl restart jenkins

6. Verify the Port Change:

http://your-jenkins-hostname:8081

12. How to secure jenkins?

Ans: Securing Jenkins is crucial to protect your CI/CD pipeline, source code, and sensitive information from unauthorized access and potential attacks. Here are several key practices and configurations to enhance Jenkins security:

1. Enable and Configure security
2. Use Authentication and authorization
3. Secure Communication
4. Access control for projects
5. Protect Sensitive data
6. Audit and Monitor
7. Hardening Jenkins configuration
8. Regular updates and backups
9. Security plugins

1. Enable and Configure Security:
   • Enable security: Go to Manage Jenkins > Configure Global Security > Check Enable security.
   • Security realm: Use Jenkins’ own user database, LDAP, Active Directory, or other authentication mechanisms.
   • Authorization: Use Matrix-based security or Role-based strategy for fine-grained access control.

2. User Authentication and Authorization:

1. Use Strong Authentication: Integrate with external authentication providers like LDAP, Active Directory, or SSO solutions. Enable multi-factor authentication (MFA) if possible.
2. Role-Based Access Control (RBAC): Implement plugins like Role-Based Authorization Strategy to define roles and permissions. Limit access to job configurations, builds, and system settings based on roles.

3. Secure Communication:

1. Secure Communication:
   • Enable HTTPS to secure communication between users and Jenkins.
   • Obtain an SSL/TLS certificate from a trusted certificate authority (CA) or use a self-signed certificate.
   • Configure Jenkins to use HTTPS by updating the Jenkins server configuration.

4. Access Control for Projects

1. Folder-Based Security:
   • Use the Folders plugin to organize projects and apply security policies at the folder level.
   • Restrict access to sensitive projects by configuring folder-level permissions.

5. Protect Sensitive Data:

1. Credentials Management: Use Jenkins’ built-in credentials store to manage passwords, SSH keys, and other sensitive data. Ensure credentials are encrypted and access is restricted to authorized jobs and users.
2. Mask Sensitive Output: Configure build logs to mask sensitive information like passwords and API keys.

6. Audit and Monitor:

1. Audit Trail: Install the Audit Trail plugin to keep a record of user actions and changes in Jenkins.Regularly review audit logs for suspicious activities.
2. Monitor Plugins: Keep plugins up-to-date to mitigate vulnerabilities. Uninstall unused plugins to reduce the attack surface.

7. Hardening Jenkins Configuration

1. Disable Unnecessary Features: Turn off Jenkins CLI if not needed. Disable the Script Console in production environments to prevent unauthorized code execution.
2. Limit External Access: Restrict access to Jenkins from external networks using firewalls and network policies. Use reverse proxies to add an additional layer of security and control over access.

8. Regular Updates and Backups

1. Keep Jenkins Updated: Regularly update Jenkins core and plugins to the latest versions to apply security patches.
2. Backup Configuration: Regularly backup Jenkins configuration and job data to restore quickly in case of a security breach or data loss.

9. Security Plugins:

Essential Security Plugins:

1. OWASP Dependency-Check Plugin: Scans for known vulnerabilities in project dependencies.
2. Matrix Authorization Strategy Plugin: Provides detailed control over permissions.
3. Role-Based Authorization Strategy Plugin: Allows setting up roles and assigning permissions based on roles.