DevOps / GitHub Actions Interview Questions

What are the key differences between GitHub Actions, Jenkins, and GitLab CI?

All three are CI/CD platforms but differ significantly in architecture, hosting model, and integration depth. Here is a direct comparison across the dimensions that matter most for a team choosing between them:

GitHub Actions vs Jenkins vs GitLab CI
Dimension	GitHub Actions	Jenkins	GitLab CI
Hosting	SaaS (GitHub-managed) or self-hosted runners	Always self-hosted; you manage the master + agents	SaaS (gitlab.com) or self-managed GitLab + runners
Config format	YAML in `.github/workflows/`	Groovy DSL in Jenkinsfile	YAML in `.gitlab-ci.yml`
Ecosystem / plugins	Actions Marketplace (thousands of actions)	1,800+ plugins; very mature but plugin conflicts common	Built-in features for SAST, DAST, registry, pages
Setup effort	Zero — create a YAML file and push	High — install, configure, maintain Jenkins server	Low on gitlab.com; moderate for self-managed
Cost model	Free for public; metered minutes for private	Free software; you pay infrastructure costs	Free tier on gitlab.com; paid tiers for more minutes/features
SCM integration	Native — deeply integrated with GitHub PRs, issues, releases	Webhook-based; GitHub plugin required	Native — deeply integrated with GitLab MRs, registry, security scans
Reusability	Reusable workflows, composite actions, Marketplace	Shared libraries, shared Jenkinsfiles	Include templates, extends, components catalog
Best for	Teams already on GitHub wanting zero-ops CI/CD	Enterprises with complex on-prem requirements and existing Jenkins investment	Teams that want a full DevSecOps platform (code → security → deploy) in one tool

In practice: if your code is on GitHub and you want to avoid managing infrastructure, GitHub Actions is the natural first choice. Jenkins wins when you have deep customisation requirements or a legacy pipeline that pre-dates modern SaaS offerings. GitLab CI is compelling when you want the full DevSecOps suite (built-in container registry, SAST, DAST, dependency scanning) without stitching together separate tools.

Take quiz

Which CI/CD platform always requires you to host and manage your own server infrastructure? GitHub Actions

✗ Try again — not quite right.

Jenkins

✓ Well done — that is correct!

GitLab CI on gitlab.com

✗ Try again — not quite right.

Both GitHub Actions and GitLab CI

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In which language/format is a Jenkins pipeline definition written? YAML in a .jenkins/ directory

✗ Try again — not quite right.

Groovy DSL in a Jenkinsfile

✓ Well done — that is correct!

JSON in pipeline.json

✗ Try again — not quite right.

HCL in a Jenkinsfile.hcl

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More Related questions...

What is GitHub Actions and what problems does it solve? What are the key components of GitHub Actions — workflows, jobs, steps, actions, and runners? How is a GitHub Actions workflow file structured, and where must it be placed? What are workflow triggers (on:) and which event types does GitHub Actions support? What is the difference between push, pull_request, and workflow_dispatch triggers? What are jobs in GitHub Actions, and how do they run in parallel by default? What are steps, and what is the difference between run: and uses: in a step? What are runners, and what is the difference between GitHub-hosted and self-hosted runners? What is the GitHub Actions Marketplace and how do you find and use actions from it? How do you use the actions/checkout action and what does it do? How do you pass environment variables and secrets to a GitHub Actions workflow? What is the difference between the env:, secrets:, and vars: contexts in GitHub Actions? How do you cache dependencies in GitHub Actions using actions/cache? How do you use matrix builds in GitHub Actions to test across multiple environments? How do you control job execution order in GitHub Actions using needs:? How do you share data between steps within a job using step outputs? How do you share build artifacts between jobs using actions/upload-artifact and actions/download-artifact? What are reusable workflows in GitHub Actions and how do you call them? What are composite actions and when should you choose them over reusable workflows? How do you set up a Docker container service for integration tests using services: in GitHub Actions? How do you use conditional steps with if: in GitHub Actions? What are the key GitHub Actions expression contexts and what information does each provide? How do you use concurrency groups to cancel outdated workflow runs in GitHub Actions? What is the GITHUB_TOKEN and what permissions does it have? How do you trigger one GitHub Actions workflow from another using workflow_run? How do you write a custom JavaScript action for GitHub Actions? How do you write a custom Docker container action for GitHub Actions? How do you implement a complete CI/CD pipeline for a container image in GitHub Actions — build, push to a registry, and deploy? How do you implement path filtering so a workflow only runs when specific files change? How do you debug failing GitHub Actions workflows — enabling debug logging and using tmate? How do you implement branch protection rules with required GitHub Actions status checks? How do you handle large monorepos with multiple services in GitHub Actions? What are OpenID Connect (OIDC) tokens in GitHub Actions and how do they replace long-lived cloud credentials? How do you prevent secret exposure and follow security hardening best practices in GitHub Actions? What are the key differences between GitHub Actions, Jenkins, and GitLab CI?

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