API Gateway
TrafficCentralized entry point that handles authentication, rate limiting, request routing, and protocol translation for your APIs.
Overview
An API Gateway is a server that acts as the single entry point for all client requests to your backend services. It handles cross-cutting concerns that would otherwise need to be duplicated across every microservice: authentication and authorization, rate limiting, request routing, protocol translation, request/response transformation, and API versioning. In Vetora's simulator, the API Gateway component models request processing overhead, routing logic, and the fan-out pattern where a single client request maps to multiple backend calls.
Authentication at the gateway is the first line of defense. The gateway validates JWT tokens, API keys, or OAuth2 credentials before any request reaches your backend services. This centralized validation ensures that unauthenticated traffic is rejected at the edge, reducing load on backend services and attack surface area. In Vetora, you can model the latency cost of token validation and observe how authentication failures affect overall throughput.
Rate limiting at the API Gateway level protects your entire system from abuse. The gateway enforces per-client, per-endpoint, or per-tenant rate limits, returning HTTP 429 responses when limits are exceeded. This is often the first and most important layer of rate limiting, complemented by more granular limiters deeper in the stack. Vetora models rate limiting algorithms (token bucket, sliding window) and shows how rate limiting affects tail latency and error rates.
Request routing is the gateway's core function. It maps incoming URL paths, HTTP methods, and headers to the appropriate backend service. Advanced routing includes canary deployments (sending 5% of traffic to a new version), A/B testing splits, and version-based routing (directing /v1/ and /v2/ requests to different service clusters). Protocol translation is equally important — the gateway can accept HTTP/REST from clients and translate to gRPC, GraphQL, or WebSocket protocols for backend communication.
API versioning through the gateway is critical for backward compatibility. As APIs evolve, the gateway can route versioned requests to the appropriate service implementation, transform request/response formats between versions, and deprecate old versions gracefully. This decouples API evolution from service deployment, allowing teams to iterate independently.
When to Use
Recommended
- +Microservices architectures requiring centralized authentication, rate limiting, and routing
- +Public-facing APIs that need versioning, throttling, and usage analytics
- +Systems requiring protocol translation between client protocols (REST/GraphQL) and backend protocols (gRPC)
- +Multi-tenant platforms where different tenants have different rate limits and access policies
- +Canary deployments and A/B testing that require traffic splitting at the request level
Not Recommended
- -Simple monolithic applications with a single backend — the gateway adds unnecessary latency and complexity
- -Internal service-to-service calls within a service mesh — use sidecar proxies (Envoy/Istio) instead
- -Ultra-low-latency paths where the gateway's processing overhead (1–5ms) is unacceptable
- -Systems where each service must independently manage its own authentication for compliance reasons
Key Parameters in Vetora
Real-World Examples
Kong Gateway
Open-source API gateway built on NGINX, with a plugin ecosystem for auth, rate limiting, logging, and transformation. Used by organizations from startups to enterprises.
AWS API Gateway
Fully managed gateway supporting REST, HTTP, and WebSocket APIs with AWS Lambda integration, IAM authentication, usage plans, and automatic scaling.
Apigee (Google Cloud)
Enterprise API management platform with developer portal, analytics, monetization, and advanced traffic management. Used by major financial and telecom companies.
Frequently Asked Questions
What is an API Gateway in microservices architecture?
An API Gateway is a server that acts as the single entry point for all client requests in a microservices architecture. It handles cross-cutting concerns like authentication, rate limiting, request routing, protocol translation, and API versioning centrally, so individual microservices don't need to duplicate this logic. This simplifies service development, reduces security attack surface, and enables centralized monitoring and traffic management.
What is the difference between an API Gateway and a Load Balancer?
A Load Balancer distributes traffic across multiple instances of the same service for availability and performance. An API Gateway routes requests to different services based on the request path, method, or headers. Load balancers work at Layer 4 (TCP) or Layer 7 (HTTP) and focus on distribution, while API Gateways work at Layer 7 and add authentication, rate limiting, transformation, and versioning. Most architectures use both: the gateway routes to the right service, and a load balancer distributes within that service's instance pool.
How does an API Gateway handle rate limiting?
API Gateways implement rate limiting using algorithms like token bucket (allows bursts up to a limit then throttles), sliding window (counts requests in a rolling time window), or fixed window (resets counters at fixed intervals). Limits are typically enforced per client (identified by API key or IP), per endpoint, or per tenant. When a client exceeds the limit, the gateway returns HTTP 429 (Too Many Requests) with a Retry-After header. In distributed deployments, rate limit counters are stored in Redis or a similar shared store.
Should I use an API Gateway with a monolithic application?
For a simple monolith with a single backend, an API Gateway adds unnecessary latency and operational complexity. However, even monoliths benefit from a gateway if you need centralized rate limiting, API key management, request logging, or if you plan to eventually decompose into microservices. The gateway provides a stable external API contract that decouples your internal architecture from client expectations, making future refactoring easier.
How does API versioning work through a gateway?
API Gateways support versioning through URL path routing (/v1/users vs /v2/users), header-based routing (Accept-Version: v2), or query parameter routing (?version=2). The gateway routes each version to the appropriate backend service or applies request/response transformations to bridge version differences. This lets you deprecate old versions gradually, run multiple versions simultaneously, and evolve your API without breaking existing clients.
Related Components
Distributes incoming traffic across multiple server instances using algorithms like round-robin, lea...
Controls request throughput using algorithms like token bucket and sliding window to protect service...
Application server or microservice that processes requests, runs business logic, and communicates wi...
Content Delivery Network that caches and serves content from edge locations close to users, reducing...
Try API Gateway in the Simulator
Build architectures with API Gateway and 13 other component types. Run discrete event simulations and get AI-powered feedback.
Open Playground