DevOps / QA Interview Q&A Bank – GitHub Markdown Version

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📁 13 - Jenkins (Scenario-Based Q&A for 5+ Years Experience)

1. Scenario: You are asked to install Jenkins and run it on a custom port 8081. How do you achieve this?

   • Edit /etc/default/jenkins or the systemd service file and change HTTP_PORT=8081.
   • Restart Jenkins: sudo systemctl restart jenkins

2. Scenario: How do you secure a freshly installed Jenkins server?

   • Enable global security and disable CLI over remoting
   • Install Role-Based Strategy Plugin
   • Configure CSRF protection and HTTPS

3. Scenario: Create users Devops and Testing with limited access in Jenkins. How do you do it?

   • Use Role-Based Strategy Plugin
   • Define roles and assign them to specific users under “Manage and Assign Roles”

4. Scenario: How do you configure Jenkins nodes (slaves) and restrict jobs using labels?

   • Assign labels under node configuration
   • In the job config, use “Restrict where this project can be run” and specify the label

5. Scenario: You have to create Jenkins jobs for this GitHub repo: https://github.com/betawins/Techie_horizon_Login_app.git. What steps do you follow?

   • Create a Freestyle or Pipeline job
   • Connect GitHub and enter repo URL
   • Add build steps like Maven or shell commands

6. Scenario: How do you configure a Jenkins job using a private GitHub repository?

   • Generate a personal access token or SSH key
   • Store credentials in Jenkins using “Credentials” plugin
   • Use those credentials in job configuration

7. Scenario: You are asked to configure two slave machines for Jenkins. What are the methods?

   • Use SSH or JNLP agent
   • Install Java on slave and connect with Jenkins master using credentials or agent.jar

8. Scenario: How do you set up a webhook to trigger a Jenkins job from GitHub?

   • Enable GitHub plugin in Jenkins
   • Set GitHub webhook URL to: http://<jenkins-url>/github-webhook/
   • Enable “GitHub hook trigger for GITScm polling” in job

9. Scenario: You want to use Poll SCM to trigger builds. What cron syntax do you use?

   • Use “Poll SCM” and define cron like: H/5 * * * * for every 5 minutes

10. Scenario: How do you configure Jenkins job for scheduled builds?

• Use “Build periodically” option and define cron syntax (e.g., @daily, H 0 * * *)

11. Scenario: You need to automate Jenkins backup using a shell script. What files do you back up?

• Backup /var/lib/jenkins/, especially jobs/, plugins/, secrets/, and config.xml

12. Scenario: Create a Bash script to back up Jenkins. How do you schedule it?

• Use tar -czf jenkins_backup.tar.gz /var/lib/jenkins
• Schedule via crontab: 0 2 * * * /path/to/script.sh

13. Scenario: What is the purpose of the ThinBackup or RethinBackup plugin?

• Automates job and config backups with scheduling, retention, and restore options

14. Scenario: You want to restore a Jenkins server from a backup. What are the steps?

• Stop Jenkins, replace contents of /var/lib/jenkins/ with backup, start Jenkins
• Ensure correct permissions and restart Jenkins service

15. Scenario: What Jenkins plugin allows you to manage fine-grained access control for different users?

• Role-Based Strategy Plugin

16. Scenario: How do you configure job chaining in Jenkins (trigger one job after another)?

• Use “Build other projects” or use Pipeline syntax with build job: 'job_name'

17. Scenario: What is a safe way to update Jenkins plugins and core?

• Use “Manage Jenkins → Plugins”, check compatibility
• Always take backup before update

18. Scenario: A Jenkins job is stuck at workspace cleanup. What could be the reason?

• File permission issues or large workspace size
• Use ws-cleanup plugin or manual cleanup script

19. Scenario: Jenkins is running out of disk space. What actions do you take?

• Clean up old builds and workspaces
• Configure build retention policies
• Archive logs and backups externally

20. Scenario: You want to notify developers on job status. How do you implement this?

• Use Email-ext plugin or integrate with Slack/MS Teams

21. Scenario: Jenkins is throwing 'Permission denied' when accessing Git repo. What are the causes?

• Incorrect SSH permissions or missing credentials in Jenkins

22. Scenario: How do you secure credentials in Jenkins Pipeline?

• Use withCredentials() block with credentials stored in Jenkins credentials manager

23. Scenario: How do you handle secrets securely in Jenkins pipelines?

• Use Jenkins credentials binding plugin and avoid echoing secrets in console

24. Scenario: Jenkins job is not triggering via webhook. How do you troubleshoot?

• Check webhook delivery logs in GitHub
• Check Jenkins logs and job trigger config

25. Scenario: Jenkins pipeline is failing due to environment mismatch. How do you ensure consistency?

• Use Docker agents or configure consistent slave environments

26. Scenario: What are best practices to ensure Jenkins stability in production?

• Limit number of concurrent jobs
• Use dedicated nodes for builds
• Regularly back up and monitor resource usage

27. Scenario: How do you configure Jenkins for CI/CD in a microservice-based repo?

• Use multibranch pipelines
• Dynamically detect services using Jenkinsfiles in subdirectories

28. Scenario: Jenkins restart loses config. How do you prevent it?

• Ensure persistent volume for /var/lib/jenkins in Docker or VM setup

29. Scenario: Restore Jenkins to a specific point after job misconfiguration.

• Use backup snapshot or GitOps-managed Jenkins configuration

30. Scenario: You want to version control Jenkins pipeline code. What’s the approach?

• Store Jenkinsfile in Git repo
• Use Job DSL or JCasC (Jenkins Configuration as Code)

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