API Gateway definition
An API gateway is a server that sits between clients and backend services and acts as the single entry point for API requests. It routes each request to the right service and handles shared concerns such as authentication, rate limiting, caching, request transformation, logging and monitoring, so individual services do not have to implement them.
How does an API gateway work?
Clients such as web apps, mobile apps and partner systems send all requests to one address, for example api.example.com. The gateway inspects each request, validates the API key or token, checks rate limits and forwards it to the right backend based on path, method or headers. /orders might go to the order service and /users to the identity service, while the client never sees the internal topology.
On the way back, the gateway can transform responses, add headers, compress payloads and cache results. It also records metrics and logs for every call, which gives operations teams one place to observe API traffic and spot errors or abuse.
Key features of an API gateway
Gateways vary in depth, but most offer the capabilities below. Popular options include Kong, Amazon API Gateway, Azure API Management, Google Apigee, Tyk and open-source proxies such as Envoy configured as an edge gateway. Managed cloud gateways reduce operational work, while self-hosted gateways give more control over plugins, latency and cost at high volume.
- Request routing and load distribution across services.
- Authentication with API keys, OAuth 2.0 and JWT validation.
- Rate limiting and quotas per client or plan.
- Response caching for frequently requested data.
- Request and response transformation, including protocol translation.
- Analytics, logging and developer portals for API consumers.
API gateway in microservices
In a microservices architecture, the gateway hides dozens of services behind a stable public interface. Teams can split, merge or move services without breaking clients. A related pattern, backend for frontend, uses a separate gateway per client type, so the mobile app receives compact responses aggregated from several services in one call.
The gateway must not become a bottleneck or a dumping ground for business logic. Keep it focused on cross-cutting concerns, run multiple instances for high availability, and treat its configuration as code with reviews and automated deployment. Watch gateway latency closely, since every request pays it.
API gateway security best practices
Because every external request passes through it, the gateway is a natural place to enforce security consistently. Validate tokens and scopes at the edge, but still check authorization inside each service, since internal calls can bypass the gateway. Apply rate limits and payload size limits to blunt abuse and denial-of-service attempts, and block HTTP methods you do not use.
Terminate TLS with modern settings, forward client identity in signed headers, and send gateway logs to your SIEM. Pair the gateway with a web application firewall to filter common attacks, and review configuration changes like code, because one wrong route can expose an internal endpoint.
Do you need an API gateway?
A single application with one API often manages fine with a reverse proxy like Nginx and authentication inside the app. A gateway becomes valuable when you expose many services, publish APIs to partners, need per-client quotas or want consistent security across teams. Nexzem sets up API gateways as part of backend and microservices projects, matching the tool to the client's cloud and traffic profile.