What are Custom Actions

Custom GitHub Actions empower you to tailor your CI/CD pipelines to meet project-specific requirements. While the GitHub Marketplace offers a wealth of community-maintained Actions—covering tasks like runtime setup, artifact transfer, Docker builds, test report syncing, and Kubernetes deployments—there are scenarios where you need:

• Project-specific logic not covered by existing Actions
• Integration with internal or legacy services
• Complex orchestration with conditional steps or custom dependencies
• Strict compliance or security policies requiring in-house solutions

Common use cases include:

• Publishing an npm package when a new Git tag is created
• Sending SMS or Slack alerts upon critical issue creation
• Deploying custom security policies or infrastructure templates

GitHub supports three main Action types. You can compare their features below:

Composite Actions

Composite Actions let you encapsulate multiple workflow steps into a single reusable unit.

# .github/actions/my-composite/action.yml
name: "My Composite Action"
description: "Install deps, run tests, and lint code"
runs:
  using: composite
  steps:
    - name: Checkout code
      uses: actions/checkout@v3
    - name: Install dependencies
      run: npm ci
    - name: Run tests
      run: npm test

• Pros: Simplifies workflows, DRY principle, cross-platform
• Cons: Can become hard to maintain if too many steps are bundled

Docker Container Actions

Container Actions run inside a Docker environment defined by you.

# .github/actions/my-docker/Dockerfile
FROM node:16
RUN npm install -g aws-cli
COPY entrypoint.sh /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

# .github/actions/my-docker/action.yml
name: "My Docker Action"
runs:
  using: docker
  image: Dockerfile
  args:
    - "--region"
    - "us-east-1"

• Pros: Full OS control, consistent environment, ideal for complex dependencies
• Cons: Linux only, requires Docker knowledge, startup overhead

JavaScript Actions

JavaScript Actions execute directly on the runner via Node.js.

// .github/actions/my-js-action/index.js
import core from "@actions/core";

async function run() {
  try {
    const name = core.getInput("name");
    core.info(`Hello, ${name}!`);
  } catch (error) {
    core.setFailed(error.message);
  }
}

run();

# .github/actions/my-js-action/action.yml
name: "My JS Action"
runs:
  using: "node16"
  main: "index.js"
inputs:
  name:
    description: "Your name"
    required: true

• Pros: Fast startup, cross-platform, simple scripting
• Cons: Less isolated—be mindful of side effects on the host runner

Select the type that best aligns with your project’s needs—whether you prioritize simplicity, isolation, performance, or cross-platform support.

• GitHub Actions Documentation
• Creating a composite run steps action
• Docker container actions
• JavaScript actions