API Gateway Architecture: The Front Door Your Microservices Need

As soon as an organization has more than three microservices, a pattern emerges: every service independently implements authentication, rate limiting, logging, CORS handling, request validation, and response transformation. The same cross-cutting concerns are implemented differently in each service, by different teams, with different quality levels and different bugs. An API gateway consolidates these cross-cutting concerns into a single, managed layer that sits in front of all services. Every request passes through the gateway before reaching any service. The gateway handles the common concerns once, consistently, and the services focus exclusively on business logic.

What an API Gateway Does

An API gateway provides six core capabilities.

• Request routing: The gateway maps incoming API requests to the appropriate backend service based on the URL path, headers, or query parameters. Clients interact with a single endpoint (api.company.com); the gateway determines which service handles each request. This decouples clients from the internal service topology: services can be refactored, split, or merged without changing the client-facing API.
• Authentication and authorization: The gateway validates API keys, JWT tokens, or OAuth credentials before the request reaches any service. Unauthorized requests are rejected at the gateway, reducing the attack surface and eliminating the need for each service to implement its own auth logic.
• Rate limiting and throttling: The gateway enforces request rate limits per client, per endpoint, or per time window. This protects backend services from traffic spikes (intentional or accidental) and ensures fair resource allocation across API consumers.
• Request/response transformation: The gateway can modify requests and responses in transit: adding headers, transforming data formats (XML to JSON), aggregating responses from multiple services into a single response, or filtering sensitive fields from responses before they reach external consumers.
• Observability: The gateway logs every request, captures latency metrics, tracks error rates, and provides a centralized view of API health. Because all traffic flows through a single point, the gateway provides comprehensive visibility that would require distributed instrumentation across every service without it.
• TLS termination: The gateway handles SSL/TLS termination, encrypting external traffic and forwarding decrypted requests to internal services over the private network. This simplifies certificate management (one certificate at the gateway rather than one per service) and reduces computational overhead on backend services.

An API gateway is not optional infrastructure for a microservices architecture. It acts as the front door providing security, observability, and operational control.

- Industry Expert

Choosing Between Managed and Self-Hosted

Cloud-managed gateways (AWS API Gateway, Azure API Management, Google Cloud Apigee) provide operational simplicity: no infrastructure to manage, automatic scaling, built-in monitoring, and pay-per-request pricing. They are the right choice for organizations that want API management capability without dedicated platform engineering. Self-hosted gateways (Kong, NGINX, Traefik, Envoy) provide maximum flexibility and control: custom plugins, advanced routing rules, deployment in any environment (cloud, on-premises, edge), and no per-request pricing at scale. They are the right choice for organizations with platform engineering teams and requirements that exceed managed gateway capabilities. The hybrid approach (a managed gateway for external APIs and a self-hosted gateway for internal service-to-service communication) is increasingly common and combines the operational simplicity of managed services with the flexibility and performance of self-hosted solutions. Designing your API architecture? Talk to Flynaut about gateway patterns and platform design at flynaut.com/application-development.