The Problem With Direct Client-to-Service Communication

When clients connect directly to backend microservices, they become tightly coupled to service interfaces. Any backend refactoring, service consolidation, or deployment change forces client updates. Mobile apps require new releases, web clients need redeployment, and third-party integrations break. The API gateway solves this by establishing a single, stable contract that clients depend on, while services evolve independently behind it.

Request routing, authentication verification, and rate limiting logic gets duplicated across services when clients connect directly. The gateway consolidates these concerns into one place, reducing code duplication and creating a consistent security posture across all ingress traffic.

Gateway Patterns for Different Client Needs

The BFF pattern creates specialized gateways where each client type gets a gateway optimized for its constraints. Mobile clients receive compact, bandwidth-conscious responses with fewer round trips. Web clients can fetch richer data structures. Internal dashboards get different rate limits and caching strategies. Each BFF remains lightweight and client-specific, routing to core backend services as needed.

Request Transformation and Aggregation at the Gateway

The gateway shields clients from internal service boundaries. When backend services split or merge, the gateway translates between the old client contract and new internal topology. A mobile client expecting a single user endpoint receives aggregated data from account service, profile service, and preferences service, all orchestrated by the gateway. This transformation layer prevents cascading changes across client codebases.

Aggregation patterns reduce round trips by combining multiple backend calls into a single gateway response. Instead of clients making five separate requests to different services, the gateway batches these calls in parallel, waits for all responses, and returns a unified payload. This is especially critical for mobile clients on high-latency networks where each round trip adds significant latency.

Applied Insight: Failure Isolation Through Circuit Breakers

Circuit breakers at the gateway prevent cascading failures. When a downstream service degrades or goes offline, the circuit breaker opens, failing fast with a cached response or fallback value instead of exhausting client timeouts and consuming resources. Without the circuit breaker, a slow backend service would cause all upstream clients to hang, overwhelming the gateway and propagating the outage upward.

Use API gateways when multiple client types exist or services need independent evolution. Use BFF specifically when client constraints differ significantly (mobile vs web) or when teams operate independently. Avoid over-engineering with gateways for simple monolithic systems or when client-to-service contracts remain stable. Measure gateway latency carefully: aggregation patterns improve client experience but add processing overhead at the gateway layer.