Git Notes

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GitHub Actions Runners

Runners are the machines that execute your GitHub Actions workflows. When a workflow is triggered, GitHub assigns it to a runner that has the appropriate...

Runners are the machines that execute your GitHub Actions workflows. When a workflow is triggered, GitHub assigns it to a runner that has the appropriate operating system and software. Understanding runners helps you optimize workflow performance, reduce costs, and handle special requirements like GPU computing or custom software installations.

What Is a Runner

A runner is a server — either hosted by GitHub or self-hosted on your own infrastructure — that listens for workflow jobs and executes them. Each job in a workflow runs on a fresh runner instance, ensuring a clean environment without leftover state from previous jobs.

When you write runs-on: ubuntu-latest in your workflow, you are telling GitHub to assign that job to one of their Ubuntu runners.

GitHub-Hosted Runners

GitHub provides managed runners that require zero setup:

yaml example

jobs:
  linux-job:
    runs-on: ubuntu-latest    # Ubuntu 22.04

  windows-job:
    runs-on: windows-latest   # Windows Server 2022

  mac-job:
    runs-on: macos-latest     # macOS 14 (Sonoma)

Available GitHub-Hosted Runner Images

Label	OS	CPU	RAM	Disk
ubuntu-latest	Ubuntu 22.04	2 cores	7 GB	14 GB
ubuntu-24.04	Ubuntu 24.04	2 cores	7 GB	14 GB
windows-latest	Windows Server 2022	2 cores	7 GB	14 GB
macos-latest	macOS 14	3 cores (M1)	7 GB	14 GB
macos-13	macOS 13	3 cores (Intel)	14 GB	14 GB

Pre-Installed Software

GitHub-hosted runners come with a rich set of pre-installed tools:

Programming languages (Node.js, Python, Java, Go, Ruby, .NET)
Package managers (npm, pip, Maven, Gradle)
Build tools (Make, CMake, Docker)
Browsers (Chrome, Firefox) for testing
Cloud CLIs (AWS CLI, Azure CLI, gcloud)
Database clients (PostgreSQL, MySQL)

Check the full list of installed software in the runner-images repository on GitHub.

Self-Hosted Runners

When GitHub-hosted runners do not meet your needs, you can set up your own:

When to Use Self-Hosted Runners

You need specific hardware (GPUs, ARM processors, more RAM)
Your builds require custom software not available on GitHub runners
You need access to internal network resources (private databases, APIs)
You want to reduce costs for large-scale builds
Regulatory requirements demand builds run on specific infrastructure

Setting Up a Self-Hosted Runner

Go to Repository Settings → Actions → Runners
Click "New self-hosted runner"
Follow the installation instructions:

bash example

# Download the runner package
mkdir actions-runner && cd actions-runner
curl -o actions-runner-linux-x64.tar.gz -L https://github.com/actions/runner/releases/download/v2.311.0/actions-runner-linux-x64-2.311.0.tar.gz
tar xzf actions-runner-linux-x64.tar.gz

# Configure the runner
./config.sh --url https://github.com/your-org/your-repo --token YOUR_TOKEN

# Start the runner
./run.sh

Using Self-Hosted Runners

yaml example

jobs:
  build:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v4
      - run: npm test

Add labels for more specific targeting:

Example

jobs: gpu-training: runs-on: [self-hosted, linux, gpu]

Runner Groups and Labels

Organize runners with labels for targeted job assignment:

Example

# Use specific hardware jobs: build-arm: runs-on: [self-hosted, ARM64] build-x64: runs-on: [self-hosted, X64] ml-training: runs-on: [self-hosted, gpu, high-memory]

Larger GitHub-Hosted Runners

For compute-intensive jobs, GitHub offers larger runners (paid):

yaml example

jobs:
  heavy-build:
    runs-on: ubuntu-latest-16-cores  # 16 CPU, 64 GB RAM

Available sizes range from 4 cores to 64 cores with proportionally more RAM and disk.

Runner Security Considerations

GitHub-Hosted Runner Security

Each job runs in a fresh VM that is destroyed after the job completes
No data persists between jobs
Runners are isolated from other customers

Self-Hosted Runner Security

Runners persist between jobs (clean up manually)
Do not use self-hosted runners for public repositories (anyone can trigger workflows via PRs)
Run the runner service with minimal privileges
Keep the runner software updated

Example

# Security best practice: restrict self-hosted runners to specific workflows jobs: deploy: runs-on: [self-hosted, production] environment: production # Requires approval

Optimizing Runner Performance

Caching

yaml example

- uses: actions/cache@v4
  with:
    path: node_modules
    key: npm-${{ hashFiles('package-lock.json') }}

yaml example

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: npm run build
      - uses: actions/upload-artifact@v4
        with:
          name: build
          path: dist/
          
  deploy:
    needs: build
    runs-on: ubuntu-latest
    steps:
      - uses: actions/download-artifact@v4
        with:
          name: build
          path: dist/

Container Jobs

Run jobs inside Docker containers on runners:

yaml example

jobs:
  test:
    runs-on: ubuntu-latest
    container:
      image: node:20-alpine
      env:
        NODE_ENV: test
    steps:
      - uses: actions/checkout@v4
      - run: npm ci && npm test

This ensures your job runs in an identical environment regardless of what the runner has installed.

Key Takeaways

Runners are the execution backbone of GitHub Actions. GitHub-hosted runners cover most use cases with zero setup, providing Linux, Windows, and macOS environments with pre-installed tools. Self-hosted runners extend capabilities for custom hardware, network access, or cost optimization. Choose the right runner type for each job — use GitHub-hosted for standard CI work and self-hosted for specialized requirements. Optimize performance with caching, artifacts, and appropriately sized runners to keep your workflows fast and efficient.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for GitHub Actions Runners.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

git-github, git & github, git, github, actions, runners, github actions runners

Related Git & GitHub Topics

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PreviousIntroduction to GitHub Actions NextGitHub Actions Workflows

Git Notes

GitHub Actions Runners

Runners are the machines that execute your GitHub Actions workflows. When a workflow is triggered, GitHub assigns it to a runner that has the appropriate...

What Is a Runner

When you write runs-on: ubuntu-latest in your workflow, you are telling GitHub to assign that job to one of their Ubuntu runners.

GitHub-Hosted Runners

GitHub provides managed runners that require zero setup:

yaml example

jobs:
  linux-job:
    runs-on: ubuntu-latest    # Ubuntu 22.04

  windows-job:
    runs-on: windows-latest   # Windows Server 2022

  mac-job:
    runs-on: macos-latest     # macOS 14 (Sonoma)

Available GitHub-Hosted Runner Images

Label	OS	CPU	RAM	Disk
ubuntu-latest	Ubuntu 22.04	2 cores	7 GB	14 GB
ubuntu-24.04	Ubuntu 24.04	2 cores	7 GB	14 GB
windows-latest	Windows Server 2022	2 cores	7 GB	14 GB
macos-latest	macOS 14	3 cores (M1)	7 GB	14 GB
macos-13	macOS 13	3 cores (Intel)	14 GB	14 GB

Pre-Installed Software

GitHub-hosted runners come with a rich set of pre-installed tools:

Programming languages (Node.js, Python, Java, Go, Ruby, .NET)
Package managers (npm, pip, Maven, Gradle)
Build tools (Make, CMake, Docker)
Browsers (Chrome, Firefox) for testing
Cloud CLIs (AWS CLI, Azure CLI, gcloud)
Database clients (PostgreSQL, MySQL)

Check the full list of installed software in the runner-images repository on GitHub.

Self-Hosted Runners

When GitHub-hosted runners do not meet your needs, you can set up your own:

When to Use Self-Hosted Runners

You need specific hardware (GPUs, ARM processors, more RAM)
Your builds require custom software not available on GitHub runners
You need access to internal network resources (private databases, APIs)
You want to reduce costs for large-scale builds
Regulatory requirements demand builds run on specific infrastructure

Setting Up a Self-Hosted Runner

Go to Repository Settings → Actions → Runners
Click "New self-hosted runner"
Follow the installation instructions:

bash example

# Download the runner package
mkdir actions-runner && cd actions-runner
curl -o actions-runner-linux-x64.tar.gz -L https://github.com/actions/runner/releases/download/v2.311.0/actions-runner-linux-x64-2.311.0.tar.gz
tar xzf actions-runner-linux-x64.tar.gz

# Configure the runner
./config.sh --url https://github.com/your-org/your-repo --token YOUR_TOKEN

# Start the runner
./run.sh

Using Self-Hosted Runners

yaml example

jobs:
  build:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v4
      - run: npm test

Add labels for more specific targeting:

Example

jobs: gpu-training: runs-on: [self-hosted, linux, gpu]

Runner Groups and Labels

Organize runners with labels for targeted job assignment:

Example

# Use specific hardware jobs: build-arm: runs-on: [self-hosted, ARM64] build-x64: runs-on: [self-hosted, X64] ml-training: runs-on: [self-hosted, gpu, high-memory]

Larger GitHub-Hosted Runners

For compute-intensive jobs, GitHub offers larger runners (paid):

yaml example

jobs:
  heavy-build:
    runs-on: ubuntu-latest-16-cores  # 16 CPU, 64 GB RAM

Available sizes range from 4 cores to 64 cores with proportionally more RAM and disk.

Runner Security Considerations

GitHub-Hosted Runner Security

Each job runs in a fresh VM that is destroyed after the job completes
No data persists between jobs
Runners are isolated from other customers

Self-Hosted Runner Security

Runners persist between jobs (clean up manually)
Do not use self-hosted runners for public repositories (anyone can trigger workflows via PRs)
Run the runner service with minimal privileges
Keep the runner software updated

Example

# Security best practice: restrict self-hosted runners to specific workflows jobs: deploy: runs-on: [self-hosted, production] environment: production # Requires approval

Optimizing Runner Performance

Caching

yaml example

- uses: actions/cache@v4
  with:
    path: node_modules
    key: npm-${{ hashFiles('package-lock.json') }}

yaml example

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: npm run build
      - uses: actions/upload-artifact@v4
        with:
          name: build
          path: dist/
          
  deploy:
    needs: build
    runs-on: ubuntu-latest
    steps:
      - uses: actions/download-artifact@v4
        with:
          name: build
          path: dist/

Container Jobs

Run jobs inside Docker containers on runners:

yaml example

jobs:
  test:
    runs-on: ubuntu-latest
    container:
      image: node:20-alpine
      env:
        NODE_ENV: test
    steps:
      - uses: actions/checkout@v4
      - run: npm ci && npm test

This ensures your job runs in an identical environment regardless of what the runner has installed.

Key Takeaways

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for GitHub Actions Runners.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

git-github, git & github, git, github, actions, runners, github actions runners

Related Git & GitHub Topics

Continue learning this concept

PreviousIntroduction to GitHub Actions NextGitHub Actions Workflows

What Is a Runner

GitHub-Hosted Runners

Available GitHub-Hosted Runner Images

Pre-Installed Software

Self-Hosted Runners

When to Use Self-Hosted Runners

Setting Up a Self-Hosted Runner

Using Self-Hosted Runners

Runner Groups and Labels

Larger GitHub-Hosted Runners

Runner Security Considerations

GitHub-Hosted Runner Security

Self-Hosted Runner Security

Optimizing Runner Performance

Caching

Artifacts for Sharing Between Jobs

Container Jobs

Key Takeaways

Continue learning this concept

What Is a Runner

GitHub-Hosted Runners

Available GitHub-Hosted Runner Images

Pre-Installed Software

Self-Hosted Runners

When to Use Self-Hosted Runners

Setting Up a Self-Hosted Runner

Using Self-Hosted Runners

Runner Groups and Labels

Larger GitHub-Hosted Runners

Runner Security Considerations

GitHub-Hosted Runner Security

Self-Hosted Runner Security

Optimizing Runner Performance

Caching

Artifacts for Sharing Between Jobs

Container Jobs

Key Takeaways

Continue learning this concept