API Gateway¶
An API gateway is a server that acts as the single entry point for all client requests to a backend system. It sits in front of a set of services and is responsible for routing requests to the appropriate service, as well as handling cross-cutting concerns that would otherwise be duplicated across services.
Typical API gateway responsibilities: request routing, which are path-based or host-based to microservices, authentication and authorisation, based on JWT validation or API key checking, rate limiting and throttling, SSL termination, request/response transformation, logging and metrics collection, and caching.
By centralising these concerns at the gateway, individual services are freed from implementing them independently. A client makes a single call to the gateway; the gateway fans out to one or more services internally.
Common API gateways: AWS API Gateway, Kong, Traefik, NGINX with Lua, and Caddy. In microservices deployments, the gateway typically sits in front of a Kubernetes ingress and routes traffic to PHP-FPM pods.
<?php
// PHP does not typically implement an API gateway itself —
// gateways are infrastructure components (Kong, Traefik, AWS API Gateway).
// PHP services sit behind the gateway and receive pre-authenticated, pre-validated requests.
// Kong plugin (Lua) enforcing JWT auth before the request reaches PHP:
// config:
// plugins:
// - name: jwt
// config:
// secret_is_base64: false
// In PHP: trust that the gateway has validated the token
// The user identity is forwarded via a header set by the gateway
$userId = (int) $_SERVER['HTTP_X_USER_ID']; // set by the gateway, not the client
// AWS API Gateway: Lambda proxy integration
// The gateway invokes a PHP Lambda function per route
// Route: GET /orders/{id} -> order-service Lambda
// BFF (Backend for Frontend): PHP as a gateway
// PHP aggregates calls to multiple microservices and returns a tailored response
$user = $userClient->get('/users/' . $userId);
$orders = $orderClient->get('/orders?user=' . $userId);
$returns = $returnClient->get('/returns?user=' . $userId);
return [
'user' => $user,
'orders' => $orders,
'returns' => $returns,
];
?>
See also API Gateway pattern — microservices.io.
Related : Microservice, Service Discovery, Rate Limiting, Authentication, Middleware Pattern, REST API, Service-Oriented Architecture (SOA)
