API Gateway: The Bouncer Your Microservices Didn’t Know They Needed
Source: Dev.to
What an API Gateway Does
An API Gateway is the person at the entrance who:
- Checks IDs (authentication/authorization)
- Controls the crowd (rate limiting, throttling)
- Directs people to the right room (routing)
- Occasionally stops someone from setting the place on fire (security, WAF)
In practice, the gateway is a single entry point for external requests. It sits in front of your services and handles common chores so each service doesn’t have to reinvent them.
| Chore | Example |
|---|---|
| Routing | GET /orders → Orders Service |
| AuthN/AuthZ | “Show me your token. No token? No entry.” |
| Rate limiting | “You’ve made 10 000 requests in 4 seconds. Please step away.” |
| Load balancing | “Instance #3 looks tired. Go to #4.” |
| Caching | “We already answered this. Here’s the cached response.” |
| Aggregation | “Client wants one response, backend needs 5 calls → combine them.” |
| Protocol translation | “Client speaks REST, service speaks gRPC → I’m bilingual.” |
Why Use a Gateway?
Without a Gateway
- Clients must know every service URL.
- Each service implements its own auth, rate limiting, logging, etc.
- Changing a service endpoint forces client changes.
With a Gateway
- One URL to rule them all – clients call a single endpoint.
- Centralized policies (security, throttling, observability).
- Backend services can evolve without breaking clients.
- Authentication/authorization is done once at the edge → less duplication and fewer inconsistencies.
- Mobile, web, and third‑party clients all hit the same gateway.
- Caching, compression, request shaping, and response aggregation reduce total calls and smooth backend load.
- One place for metrics, logs, tracing correlation, and global policies.
- Easier versioning (
/v1,/v2) without forcing every service to carry legacy baggage.
Drawbacks & Trade‑offs
- Added component → another potential point of failure.
- If the gateway goes down, the whole API surface is unavailable.
- It introduces an extra hop, which adds latency (usually acceptable).
- Requires good configuration; over‑loading it with plugins can turn it into a “Christmas tree” of features.
- Managed gateways cost money; self‑hosted gateways cost engineering effort.
- Some solutions lock you into a specific cloud ecosystem.
Traffic Types & Placement
| Traffic | Typical Layer | Typical Concerns |
|---|---|---|
| North‑south (client → service) | L4/L7 (network or application) | Auth, rate limiting, versioning, transformation, aggregation |
| East‑west (service → service) | L4/L7 inside the cluster | mTLS, retries, circuit breaking, traffic shaping |
Gateways can coexist with service‑mesh data planes; in serious systems they often do.
Popular API Gateway Solutions
- AWS API Gateway – common in serverless setups (
API Gateway → Lambda). - Kong – popular in Kubernetes and microservices; plugin‑driven, highly extensible.
- NGINX – can be configured as a gateway/reverse proxy with fine‑grained control.
- Traefik – cloud‑native router with auto‑discovery features.
Pick based on your environment, governance needs, and how much platform engineering you want to own.
When to Use a Gateway
- Multiple services and multiple client types.
- Need for centralized security, throttling, and monitoring.
- Desire for a stable external API while internal services evolve.
When You Might Skip It
- Tiny system with a single service (for now).
- No cross‑cutting policies required yet.
- You prefer not to operate additional infrastructure.
Analogy Recap
| Role | API Gateway Equivalent |
|---|---|
| Front door | One entry point |
| Bouncer | Auth and quotas |
| Traffic cop | Routing and load balancing |
| Translator | Protocol and payload shaping |
| Receptionist | Aggregation and consistent error responses |
Key Considerations for Production
- High availability – multi‑instance, multi‑zone deployment.
- Observability – metrics, logs, tracing.
- Security controls – auth, mTLS/TLS, optional WAF integration.
- Rate limits / quotas – protect backend resources.
- Deployment strategy – blue/green or canary for config changes.
- Clear ownership – someone must maintain the gateway.
Conclusion
API Gateways are not magic; they concentrate responsibility. Done well, they simplify routing, security, and observability across a microservice landscape. Done poorly, they become an expensive bottleneck and the first place everyone blames when things go wrong.
If you’re building microservices, you’ll probably end up with a gateway anyway—might as well do it intentionally.
Want a follow‑up? I can write part 2 on “API Gateway vs. API Management” or “Kubernetes: Ingress vs. Gateway API vs. Service Mesh” with real deployment patterns.