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Maven / GitHub Actions Interview Questions

What are jobs in GitHub Actions, and how do they run in parallel by default?

A job is a named collection of steps that runs on a single runner from start to finish. Every job gets a fresh, isolated virtual machine (or container), so jobs do not share filesystem state, environment variables, or processes with each other unless you explicitly pass data via artifacts or outputs.

When a workflow contains multiple jobs, GitHub schedules all of them simultaneously by default — there is no implicit ordering. GitHub's scheduler picks up each job as soon as a runner is available, so two jobs in the same workflow can and do run at the same time:

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm run lint

  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm test

In this example, lint and test start at the same time on two separate Ubuntu runners. This parallelism is a deliberate design choice: independent tasks like linting, unit testing, and security scanning should not wait for each other.

To make jobs run sequentially, use needs: to declare that one job depends on another. You can also use if: always() combined with needs: to run a cleanup job even if a dependency failed.

Each job also independently declares its own runs-on: label, meaning different jobs in the same workflow can target different runner types — one job on Ubuntu, another on macOS, another inside a custom self-hosted runner with GPU access.

By default, how do multiple jobs defined in the same GitHub Actions workflow execute?
What does each job in a GitHub Actions workflow receive by default to run its steps?

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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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