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DevOps / GitHub Actions Interview Questions

What are the key components of GitHub Actions — workflows, jobs, steps, actions, and runners?

GitHub Actions is built from five composable pieces that work together to automate your software development lifecycle.

  • Workflow — A YAML file stored in .github/workflows/. A workflow describes when automation should run (the trigger) and what it should do (one or more jobs). A repository can have many workflows running independently.
  • Job — A set of steps that execute on the same runner. All steps in a job share a filesystem and environment. By default, jobs in the same workflow run in parallel unless you declare dependencies with needs:.
  • Step — An individual task inside a job. A step either runs a shell command (run:) or calls a reusable action (uses:). Steps within a job run sequentially and share the job's working directory.
  • Action — A reusable unit of automation. An action can be a JavaScript program, a Docker container, or a composite shell script. You reference actions from the Marketplace (e.g. actions/checkout@v4) or from your own repository. Actions receive inputs and can produce outputs for downstream steps.
  • Runner — The machine that actually executes a job. GitHub provides hosted runners (Ubuntu, Windows, macOS) that are provisioned fresh for every job. You can also register self-hosted runners on your own infrastructure for larger workloads, custom tooling, or network access to private systems.

The hierarchy is: one workflow contains many jobs; each job runs on a runner and contains many steps; each step optionally calls an action. Understanding this hierarchy explains almost every YAML property you will encounter in GitHub Actions.

In GitHub Actions, what is a 'step' within a job?
Which GitHub Actions component is the machine that actually executes job steps?

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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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