API Gateway - A Boon!

API Gateway

An API gateway is a mechanism for managing APIs that sits in the middle of a client and a collection of backend services. An API gateway serves as a reverse proxy, accepting all API requests, aggregating the various services needed to fulfil them, and returning the necessary result.

API Gateway responsibilities

  • Authentication
  • Response caching
  • Rate Limiting
  • Request Logging
  • Payload Transformation
  • Header Injection / Removal
  • Message Logging
  • Monitoring
  • Alerts

The Problem:

Let's say we are making an e-commerce website/app. There are separate microservices like:

  • Product Catalog Service
  • Order Service
  • Recommendation Service
  • Inventory Service
  • Cart Service

There are multiple ways of orchestrating these APIs but let's talk about the first approach where we don't use an API Gateway:

Direct API Calls to backend services
API Without Gateway

Each backend APIs will have a load balanced public endpoint which can be called by the client directly. Therefore, to retrieve just the products available, the client would be making multiple REST API calls to all these services.

Problems?

Well there are many. Let's see few:

  • Performance is impacted by client-side composition logic and numerous API calls.
  • Clients are tightly coupled with services, making it difficult to keep them up to date.
  • Services are compelled to use contact protocols that are supported by the client.

Here's where , API Gateway comes to Rescue!!

Gateway to Rescue
The API Gateway Approach
API with Gateway

The API Gateway is like a single entry point into a system. IT encapsulates all the internal system architecture and provides an API for a tailored client experience.

It can also have additional responsibilities like, monitoring, caching, payload transforming, authentication to name a few.

Request routing, composition, and protocol translation are all handled by the API Gateway. All client requests are routed via the API Gateway first. Requests are then routed to the relevant microservice. Frequently, the API Gateway can process a request by invoking several microservices and aggregating the output. It can translate between web protocols such as HTTP and WebSocket and web‑unfriendly protocols that are used internally.

Therefore API Gateway is the way

The API Gateway can also build a custom API for each client. For mobile clients, it usually exposes a coarse API. Consider the following scenario: product info. The API Gateway will provide an endpoint (/productdetails?productid=xxx) that allows a mobile client to request all of the product details in one go.

Benefits and Drawbacks of API Gateway

Benefits

  • It encapsulates the internal structure of the application.
  • Custom endpoint for clients
  • Avoid multiple round up API calls
  • Can add API specifications(OAS, RAML etc.) to help discover API better

Drawbacks

  • Additional dev effort on developing and managing these wrappers
  • Has to be highly available and scalable

API gateway design issues

Following issues should be considered while developing an API gateway

  • Performance & scalability ( Sync I/O vs Async I/O model)
  • Writing maintainable code by using reactive programming
  • Service Discovery
  • Handling partial failure ( Running multiple instances, timeout, circuit breaker, and fallback mechanisms)

Implementing API Gateway

There are a couple of different ways to implement API gateway

  • API gateway product/service
  • Developing own API Gateway

Popular API Gateway Services

  • AWS API Gateway
  • MuleSoft
  • IBM Redhat
  • Google Apigee
Conclusion

API Gateway is one that piece in your architecture that can make your client's API experience better and more tailored. It also enables you to handle some Non Functional Requirements at Gateway level to keep your backend/implementation API clean of clutter.

Hope you liked it!

Tirthankar Kundu

Tirthankar Kundu