What is api-gateway?

An API gateway is a single entry point that sits in front of a group of backend services (like micro‑services). It receives all incoming API requests from clients (web apps, mobile apps, etc.), forwards them to the appropriate service, and then returns the response to the client. Think of it as a receptionist that directs visitors to the right department inside a company.

Let's break it down

  • Client request: A user or app sends an HTTP request (GET, POST, etc.) to the gateway.
  • Routing: The gateway looks at the request path, method, or headers and decides which backend service should handle it.
  • Transformation: It can modify the request (e.g., add authentication tokens) or change the response format (e.g., convert XML to JSON).
  • Security: The gateway can enforce authentication, rate limiting, and IP filtering before the request reaches any service.
  • Aggregation: It can call multiple services, combine their results, and send a single response back to the client.
  • Monitoring: It logs traffic, measures latency, and can trigger alerts if something goes wrong.

Why does it matter?

  • Simplifies client code: Clients only need to know one URL instead of many different service endpoints.
  • Centralizes cross‑cutting concerns: Security, logging, throttling, and versioning are handled in one place, not duplicated across services.
  • Improves performance: By caching responses or aggregating data, the gateway can reduce the number of round‑trips a client makes.
  • Enables rapid evolution: Backend services can change internally without breaking existing client integrations, as long as the gateway maintains the public contract.

Where is it used?

  • Micro‑service architectures: Companies like Netflix, Amazon, and Uber use API gateways to manage hundreds of services.
  • Serverless platforms: Services such as AWS API Gateway sit in front of Lambda functions.
  • Enterprise APIs: Organizations expose public or partner APIs through a gateway to enforce policies and monitor usage.
  • Mobile back‑ends: Mobile apps often call a gateway that handles authentication, data shaping, and versioning for different app releases.

Good things about it

  • Provides a unified, consistent interface for all clients.
  • Central point for implementing security, rate limiting, and analytics.
  • Can reduce latency with caching and request/response transformation.
  • Makes it easier to version APIs without breaking existing consumers.
  • Enables request aggregation, so a client can get data from multiple services in one call.

Not-so-good things

  • Becomes a single point of failure if not deployed with high availability.
  • Adds an extra network hop, which can increase latency if not optimized.
  • Complex routing or heavy transformation logic can make the gateway a performance bottleneck.
  • Requires careful configuration; mis‑configured policies can unintentionally block legitimate traffic.
  • Over‑reliance on the gateway may lead to “gateway sprawl” where too many responsibilities are crammed into one component.