DevOps / GitHub Actions Interview Questions

What are runners, and what is the difference between GitHub-hosted and self-hosted runners?

A runner is the server (physical or virtual) that picks up a queued job and executes its steps. GitHub manages a global pool of hosted runners; alternatively you can register your own machines as self-hosted runners for full control over the environment.

GitHub-Hosted vs Self-Hosted Runners
Dimension	GitHub-Hosted	Self-Hosted
Setup	Zero configuration — use labels like `ubuntu-latest`, `windows-latest`, `macos-latest`	You install the runner agent on your own server and register it with your repo/org
Environment	Fresh VM per job; pre-installed with common tools (Node, Java, Docker, etc.)	Persistent; you control what is installed; jobs share the same machine state
Cost	Free for public repos; metered minutes for private repos	No GitHub billing for compute; you pay for your own infrastructure
Performance	Standard 2-core / 7 GB (Linux); larger runners available at extra cost	As powerful as your hardware allows; good for GPU jobs or large build caches
Network access	Public internet only	Can reach private VPC resources, on-premise databases, etc.
Security	Isolated per run; safe for public repos	Risky for public repos — malicious PRs can run code on your machines

For most teams GitHub-hosted runners are the right starting point. Self-hosted runners make sense when you need private network access, specialised hardware (GPU, ARM), or very long build times where hosted-runner costs become significant.

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Which runner label would you use in runs-on: to request a fresh Linux VM managed by GitHub? linux-latest

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ubuntu-latest

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hosted-linux

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github-runner

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Why can self-hosted runners be a security risk when used with public repositories? They cannot access the internet

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Pull requests from forks can execute arbitrary code on your own machines

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They do not support Docker containers

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GitHub cannot monitor their activity

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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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