Skip to main content
Version: Next

API Gateway (Composer Service)

The Composer Service is an API Gateway that runs within Watt (the Node.js Application Server). It automatically integrates multiple microservices into a unified API ecosystem, providing a single public endpoint for clients while managing routing, composition, and conflict resolution behind the scenes.

The Composer Service aggregates APIs from multiple sources - whether they're other services in your Watt application, external APIs, or legacy systems - presenting them as a cohesive, well-documented API to your clients.

For a high level overview of how Watt and its services work, please reference the Overview guide.

Features​

  • Service Discovery: Automatically discover and compose APIs from multiple services in your Watt application
  • OpenAPI Composition: Combine multiple OpenAPI specifications into a single, unified API documentation
  • GraphQL Federation: Aggregate GraphQL schemas from multiple services with Apollo Federation support
  • Conflict Resolution: Intelligent handling of endpoint conflicts and path overlaps between services
  • Route Prefixing: Organize APIs with automatic or custom path prefixing for each service
  • Dynamic Updates: Real-time schema updates when underlying services change (in development mode)
  • Custom Logic: Extend with Fastify plugins for authentication, rate limiting, or request transformation

When to Use Composer Service​

Composer Service is ideal for:

  • Microservices Architecture: Present a unified API from multiple independent services
  • API Aggregation: Combine internal and external APIs into a single public interface
  • Legacy Integration: Gradually modernize by composing new and legacy APIs
  • Team Boundaries: Allow different teams to own services while providing unified client experience
  • API Versioning: Manage different API versions while maintaining client compatibility
  • Client Simplification: Reduce client complexity by handling service discovery and routing

Quick Start​

Create a Composer Service within a Watt application:

# Create a new Watt application
wattpm create my-gateway

# Add multiple services to compose
# (This will prompt you through the service setup)
cd my-gateway

# Start in development mode
wattpm dev

Your Composer Service will automatically discover other services in your Watt application and create a unified API. Visit http://localhost:3042/documentation to see the composed API documentation.

For service-specific configuration and advanced usage, see the Configuration guide.

Issues

If you run into a bug or have a suggestion for improvement, please raise an issue on GitHub or join our Discord feedback channel.