saas-api-gateway

A BFF API gateway pattern routes SaaS traffic securely through centralized proxy modules using Fastify reply.from. It forwards client requests to downstream microservices while keeping controllers thin and free of domain logic.

Fastify reply.from enables proxy routing by forwarding client requests to downstream services. In an NX monorepo, you register reply.from, copy the proxy module pattern, and use centralized proxy constants for prefix stripping and route transformation.

Neverthrow handles proxy-result errors by wrapping HttpProxyService operations in Result types. This guards against invalid URLs and proxy failures, providing uniform error handling for every proxied client request.

Yes, Fastify proxy routing works with NestJS guards for authentication. The SaaS API gateway requires uniform guard conventions for each controller, ensuring client requests are authenticated consistently before being forwarded to downstream services.

The best way to add a downstream service to a BFF API gateway is to copy the proxy module pattern, register it in AppModule, and configure centralized proxy constants. Controllers stay two lines to separate proxy routing from domain logic.

API gateway controllers should avoid Prisma and domain logic to prevent duplicating business rules. The BFF pattern enforces thin controllers, ensuring the gateway only authenticates, proxies, and error-handles requests without mixing in domain concerns.