Top 50 GitHub Actions Interview Question and Answers

06 Oct 2024 - Shyam Mohan

1. What is GitHub Actions?

   • GitHub Actions is a CI/CD platform that enables automation directly within GitHub repositories for building, testing, and deploying code.

2. How do workflows work in GitHub Actions?

   • Workflows are automated processes defined in YAML files under .github/workflows and are triggered by specific events, such as push or pull_request.

3. What are jobs in GitHub Actions?

   • Jobs are individual tasks that run within workflows. Each job can include multiple steps and can run in parallel or sequentially.

4. Explain steps in GitHub Actions.

   • Steps are the individual tasks executed in a job. They can be custom shell commands or actions.

5. What are runners in GitHub Actions?

   • Runners are servers that execute workflows. GitHub provides hosted runners, or you can use self-hosted runners for custom environments.

6. What’s the difference between GitHub-hosted and self-hosted runners?

   • GitHub-hosted runners are managed by GitHub and provide common tools. Self-hosted runners are managed by users for custom configurations.

7. How do you define a workflow trigger in GitHub Actions?

   • Workflow triggers are defined using the on keyword, specifying events like push, pull_request, or schedule.

8. What are reusable workflows in GitHub Actions?

   • Reusable workflows allow common tasks to be centralized in one workflow file and invoked in multiple repositories.

9. What are artifacts in GitHub Actions?

   • Artifacts are files generated by workflows (e.g., build files) that can be saved and shared across jobs or with users.

10. How do you manage secrets in GitHub Actions?

    • Secrets are stored in GitHub repository settings and accessed in workflows using $ syntax.

11. How can you run a job only on specific branches?

    • Specify branches under the on condition, e.g., on: push: branches: [main, dev].

12. What is a matrix strategy in GitHub Actions?

    • Matrix strategy runs a job multiple times with different configurations (e.g., OS, Node.js versions).

13. Explain how caching works in GitHub Actions.

    • GitHub Actions supports caching dependencies to speed up workflow execution using the actions/cache action.

14. What is needs in GitHub Actions?

    • needs is used to define job dependencies, ensuring jobs run sequentially when necessary.

15. How do you add conditional logic to GitHub Actions workflows?

    • Use if statements to define conditions, such as if: success() or if: always().

16. What is the purpose of continue-on-error?

    • continue-on-error: true allows a job to proceed even if a step fails.

17. What is a composite action?

    • A composite action bundles multiple steps in one action, making it reusable.

18. How do you pass environment variables across jobs?

    • Use env for global or job-level variables or pass them as outputs between jobs.

19. How do you debug workflows in GitHub Actions?

    • Use ::debug:: commands, review logs, or set up ACTIONS_RUNNER_DEBUG in secrets for verbose logging.

20. How do you run scheduled workflows?

    • Use on: schedule with a cron syntax (e.g., cron: '0 0 * * 1' for weekly triggers).

21. How do you reuse workflows across repositories?

    • Use reusable workflows by referencing them in other repositories with the uses syntax.

22. How do you handle secrets in workflows safely?

    • GitHub Actions masks secrets automatically and restricts them from appearing in logs.

23. What is the purpose of job.container?

    • job.container allows running jobs inside a Docker container for isolated environments.

24. What is jobs.<job_id>.outputs?

    • Outputs are values that can be set in a job and accessed by dependent jobs.

25. Explain the purpose of the env keyword.

    • env defines environment variables for steps, jobs, or workflows.

26. How can you use a Docker image in GitHub Actions?

    • Define container: image: <docker-image> in the job or use Docker commands in steps.

27. How do you specify a particular runner version?

    • Choose an OS version (e.g., runs-on: ubuntu-latest or runs-on: windows-2019).

28. What’s the purpose of jobs.<job_id>.timeout-minutes?

    • This sets a timeout for the job, after which it’s automatically canceled.

29. What is a service container?

    • Service containers are additional containers run alongside jobs, useful for databases or message queues.

30. What’s the difference betweenactions/checkout@v2 and actions/checkout@v3?

    • Each major version may introduce performance improvements and bug fixes; v3 includes enhancements over v2.

31. What are custom actions?

    • Custom actions are user-defined tasks created in JavaScript or Docker that can be reused across workflows.

32. How do you use GitHub Actions with multiple repositories?

    • Use checkout with repository names or trigger workflows across repos using repository_dispatch.

33. What is concurrency in GitHub Actions?

    • Concurrency controls simultaneous runs of workflows, allowing them to cancel previous runs if needed.

34. How can you prevent secrets from leaking?

    • Mask secrets in logs, avoid set-output with secrets, and use secrets safely in workflows.

35. How do you handle GitHub Actions permissions?

    • Set granular permissions for actions in the repository settings or permissions keyword in workflows.

36. What is the purpose of GITHUB_TOKEN?

    • GITHUB_TOKEN is an auto-generated token providing access to the repo for secure API interactions.

37. What is jobs.<job_id>.strategy.fail-fast?

    • It stops all jobs in a matrix if any job fails, reducing resource use.

38. How do you manage workflow concurrency?

    • Use concurrency to limit simultaneous runs or cancel redundant runs with cancel-in-progress.

39. What are required status checks in GitHub Actions?

    • These are checks that must pass before merging, typically set in branch protection rules.

40. Explain the purpose of jobs.<job_id>.defaults.

    • defaults provides default run settings for steps in a job.

41. How do you handle errors in GitHub Actions?

    • Use if: failure() for error handling, or add continue-on-error for steps that shouldn’t block progress.

42. What are the best practices for securing workflows?

    • Avoid exposing secrets, validate inputs, and use reusable actions from trusted sources.

43. How can you optimize GitHub Actions for performance?

    • Use caching, parallel jobs, matrix builds, and reusable workflows.

44. How do you troubleshoot failed workflows?

    • Check logs, enable debug logging, and use the ::debug:: command.

45. What’s the purpose of jobs.<job_id>.env?

    • env at the job level sets environment variables available to all steps in that job.

46. How do you create a GitHub Action using JavaScript?

    • Create an action.yml file, define inputs, and use JavaScript to build the action logic.

47. What’s the role of jobs.<job_id>.if?

    • if allows conditional job execution based on specific criteria.

48. What is on.workflow_call?

    • on.workflow_call triggers a reusable workflow, allowing it to be called from other workflows.

49. How can you share artifacts across jobs?

    • Use upload-artifact to save files in one job and download-artifact to access them in another.

50. What are the benefits of GitHub Actions over other CI/CD tools?

    • GitHub Actions provides native GitHub integration, reusable workflows, strong community support, and flexible automation.