Understanding API Gateways

Koushith

I've been diving into modern architecture components, specifically API Gateways. If you are working with microservices, this is a core component you need to understand.

The Hotel Analogy:

Think of an API Gateway like a luxury hotel's front desk.

Just like hotel guests don't need to know exactly where the housekeeping room or maintenance room is located, your clients don't need to know about the internal structure of your microservice architecture. The gateway handles that coordination for you.

An API Gateway serves as a single entry point for all client requests, managing and routing them to the appropriate backend service. It manages centralized middleware tasks like authentication, routing, and request handling.

Without an API Gateway, the client would need to know exactly where to go to make a request. It is designed to be a thin, relatively simple component that serves a clear purpose.

Visualizing the Flow

Here is how the request flows from the client, through the gateway logic, and to the backend services.

Click to expand

Core Responsibilities

The gateway handles a few critical jobs:

1. Request Validation Before doing anything else, the API Gateway checks if incoming requests are properly formatted and contain all the required info (headers, URLs, body, etc.). If something is wrong, the gateway can quickly reject it and send back a helpful error message.

2. Middleware The gateway can be configured to handle various middleware tasks so your services don't have to. Common examples include:

  • Authentication (JWT, etc.)
  • Rate Limiting
  • SSL Termination
  • Logging and Traffic Monitoring
  • Handling CORS
  • Whitelisting/Blacklisting

3. Request Routing It determines which backend service should handle each incoming request. Here is what a typical routing config might look like:

routes:
  - path: /users/*
    service: user-service
    port: 8080
  - path: /orders/*
    service: order-service
    port: 8081
  - path: /payments/*
    service: payment-service
    port: 8082

4. Transforming While most services communicate via HTTP, in some cases your backend service might use a different protocol like gRPC for internal communication. The gateway can transform the request to match the appropriate format (e.g., converting JSON to Protobuf and back again).

5. Caching Before sending the response back to the client, the gateway can optionally cache the response. This can be done in-memory or using a distributed cache like Redis.

Scalability

API Gateways are stateless and can be scaled horizontally. You can keep the API Gateway closer to the user, similar to how you do for a CDN.

If you are looking for tools, here are the common ones:

  • Cloud: AWS API Gateway, Azure API Management, Google Cloud Endpoints.
  • Open Source: Express Gateway, Kong, Tyk.

TL;DR

Use an API Gateway when you have multiple microservices. Without it, everything is tightly coupled, and the client would need to know how to communicate with multiple services directly.

Used LLMs to correct grammar, typos etc

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