Instead of making each small service in a microservices system handle security, what central component can apply authentication and rate limiting for all requests before they reach the services?

The central component that can apply authentication and rate limiting for all requests before they reach the services in a microservices system is an API Gateway. An API Gateway acts as the single entry point for all client requests entering a microservices system. It functions as a reverse proxy, routing incoming requests to the appropriate backend microservices, which are small, independent services that together form an application. By centralizing these concerns, individual services can focus purely on their specific business logic without needing to implement security measures themselves.

For authentication, the API Gateway intercepts every incoming request. Authentication is the process of verifying the identity of a client or user. Instead of each microservice performing this check, the Gateway is configured to interact with an Identity Provider or an authentication service. It inspects the request for a valid authentication credential, such as a JSON Web Token (JWT) or an API key. If the credential is missing or invalid, the Gateway rejects the request immediately, preventing unauthorized access. If the credential is valid, the Gateway typically adds the authenticated user's identity information to the request header before forwarding it to the target microservice. This offloads the responsibility of authentication from individual services.

For rate limiting, the API Gateway also intercepts requests and controls the number of requests a specific client can make within a defined time period. Rate limiting is a mechanism to prevent abuse, protect services from overload, and ensure fair usage of resources. The Gateway tracks the request count for each client, usually identified by their IP address or a user ID from an authentication token. If a client exceeds a configured threshold, for example, 100 requests per minute, the API Gateway will block subsequent requests from that client for a set duration. It typically responds with an HTTP 429 Too Many Requests status code. This centralized approach ensures that all services behind the Gateway are protected consistently from excessive traffic without each service needing to implement its own rate limiting logic.