Reverse Proxy vs API Gateway

1. What Is a Reverse Proxy?

A Reverse Proxy is a server that sits between clients and backend servers. It receives client requests and forwards them to the appropriate backend server. It then returns the backend response to the client.

The client communicates with the reverse proxy instead of connecting directly to the backend servers.

Architecture Diagram

How It Works

A client sends an HTTP request to the reverse proxy.
The reverse proxy determines which backend server should receive the request.
It forwards the request to that server.
The backend server processes the request and returns a response.
The reverse proxy forwards the response to the client.

Key Responsibilities

Request routing: Forwards requests to the appropriate backend server.
Load balancing: Distributes requests across multiple backend instances.
TLS termination: Can handle HTTPS connections and forward requests internally.
Security: Can help shield backend servers from direct public access.
Caching: Can cache eligible responses when configured.
Compression: Can compress responses when supported and configured.
Health checks and failover: Some reverse proxies can avoid unhealthy backend instances and redirect traffic to healthy ones.

Examples of Reverse Proxy Software

Nginx
HAProxy
Microsoft YARP (Yet Another Reverse Proxy)
Envoy Proxy
Apache HTTP Server with proxy modules

Important: A reverse proxy is a traffic-handling role, not a fixed list of features. The available capabilities depend on the product and its configuration.

2. What Is an API Gateway?

An API Gateway is an entry point for client requests to backend APIs and services. It routes requests and can apply centralized API policies such as authentication, authorization, rate limiting, request transformation, API versioning, and monitoring.

An API gateway commonly uses reverse-proxy functionality to forward requests. However, its responsibilities often extend beyond basic traffic forwarding.

Architecture Diagram

How It Works

A client sends a request to the API gateway.
The gateway applies configured policies, such as authentication and rate limiting.
It routes the request to the appropriate backend API.
The backend processes the request and returns a response.
The gateway applies any required response policies and returns the response to the client.

Key Responsibilities

API routing: Routes requests to the correct API or microservice.
Authentication: Validates credentials or tokens when configured.
Authorization: Enforces configured access policies.
Rate limiting: Restricts request rates to help protect services.
API versioning: Routes requests to the appropriate API version.
Request and response transformation: Modifies headers, paths, or payloads where supported.
Observability: Supports centralized logging, metrics, and tracing.
API aggregation: Some gateways can combine responses from multiple backend APIs.
Policy enforcement: Applies consistent rules across exposed APIs.

Examples of API Gateway Products

Azure API Management
Amazon API Gateway
Apigee API Management
Kong Gateway
Self-hosted gateways built using products such as YARP with additional middleware and policies

Important: Not every API gateway supports every capability out of the box. Features such as API subscriptions, developer portals, analytics, and API product management depend on the chosen product.

3. Reverse Proxy vs API Gateway: Main Difference

The main difference is the scope of responsibility.

A reverse proxy primarily handles traffic between clients and backend servers.
An API gateway focuses on exposing and governing APIs, often using reverse-proxy functionality together with API-specific policies.

An API gateway is commonly implemented using reverse-proxy capabilities, but a reverse proxy does not automatically provide all API management features.

4. Detailed Comparison Table

Feature	Reverse Proxy	API Gateway
Primary Purpose	Forward and manage traffic to backend servers.	Expose, route, secure, and govern APIs.
Request Routing	Yes	Yes
Load Balancing	Common capability	Available in many products, depending on configuration
TLS Termination	Common capability	Common capability
Authentication	May be supported through configuration or extensions	Commonly supports centralized API authentication policies
Authorization	Depends on configuration and extensions	Commonly supports centralized API access policies
Rate Limiting	May be supported	Common API policy; exact capabilities vary
API Versioning	Can route by path or header when configured	Often provides API-specific version routing and management
Request Transformation	May support header and path rewriting	May support API-oriented header, path, or payload transformation
API Aggregation	Not a standard basic reverse-proxy responsibility	Supported by some gateways or through additional components
Developer Portal and API Products	Generally not a core reverse-proxy feature	Available in API management platforms such as Azure API Management
Monitoring	Traffic logs and metrics can be available	API-level monitoring and analytics may be available
Typical Use	Web traffic, load balancing, and protecting backend servers	Public APIs, mobile backends, and microservice API governance

5. ASP.NET Core Example Using YARP as a Reverse Proxy

YARP (Yet Another Reverse Proxy) is a Microsoft-supported toolkit for building reverse proxies using ASP.NET Core.

Suppose you have two backend services:

User Service: https://localhost:7001
Product Service: https://localhost:7002

The reverse proxy routes requests according to their URL paths.

Architecture

Client
  |
  v
YARP Reverse Proxy
  |
  +-- /users/*    ------> User Service
  |
  +-- /products/* ------> Product Service

Configuration: appsettings.json

{
  "ReverseProxy": {
    "Routes": {
      "users": {
        "ClusterId": "usersCluster",
        "Match": {
          "Path": "/users/{**catch-all}"
        }
      },
      "products": {
        "ClusterId": "productsCluster",
        "Match": {
          "Path": "/products/{**catch-all}"
        }
      }
    },
    "Clusters": {
      "usersCluster": {
        "Destinations": {
          "destination1": {
            "Address": "https://localhost:7001/"
          }
        }
      },
      "productsCluster": {
        "Destinations": {
          "destination1": {
            "Address": "https://localhost:7002/"
          }
        }
      }
    }
  }
}

Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddReverseProxy()
    .LoadFromConfig(
        builder.Configuration.GetSection("ReverseProxy"));

var app = builder.Build();

app.MapReverseProxy();

app.Run();

Install the YARP reverse-proxy package appropriate for your project before using this configuration.

Example Requests

Client Request	Destination
`https://localhost:5000/users/10`	User Service at `https://localhost:7001/users/10`
`https://localhost:5000/products/20`	Product Service at `https://localhost:7002/products/20`

This example demonstrates reverse-proxy routing. It does not automatically implement API authentication, authorization, rate limiting, API subscription management, or a developer portal. Those capabilities must be added or provided by the surrounding platform as needed.

6. Can YARP Be Used to Build an API Gateway?

Yes. YARP provides reverse-proxy routing and extensibility. You can build an API gateway by combining it with appropriate ASP.NET Core middleware, authentication, authorization, rate limiting, observability, and other required policies.

Example Architecture

Client
  |
  v
YARP-Based API Gateway
  |
  +-- Authentication Middleware
  |
  +-- Authorization Policies
  |
  +-- Rate Limiting
  |
  +-- Logging and Tracing
  |
  +-- API Routing
  |
  +-- User Service
  +-- Booking Service
  +-- Payment Service

Example: Add Authentication and Rate Limiting

The following is a simplified illustration of configuring authentication and rate limiting in ASP.NET Core. It assumes that the relevant authentication scheme has been configured correctly and that the YARP routes and clusters are defined.

using System.Threading.RateLimiting;
using Microsoft.AspNetCore.Authentication.JwtBearer;

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddAuthentication(
        JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Authority = "https://identity.example.com";
        options.Audience = "api";
    });

builder.Services.AddAuthorization();

builder.Services.AddRateLimiter(options =>
{
    options.AddFixedWindowLimiter("api", limiter =>
    {
        limiter.PermitLimit = 100;
        limiter.Window = TimeSpan.FromMinutes(1);
        limiter.QueueLimit = 0;
    });
});

builder.Services
    .AddReverseProxy()
    .LoadFromConfig(
        builder.Configuration.GetSection("ReverseProxy"));

var app = builder.Build();

app.UseAuthentication();
app.UseAuthorization();
app.UseRateLimiter();

app.MapReverseProxy()
   .RequireAuthorization()
   .RequireRateLimiting("api");

app.Run();

Production considerations: Replace the example identity authority and audience with valid configuration. Validate tokens, configure trusted identity providers, apply appropriate rate-limit policies, and ensure backend services cannot be accessed through unintended public routes. Depending on the application, you may also need route-specific authorization, trusted forwarding-header handling, timeouts, health checks, and distributed rate limiting.

A dedicated API management product may be preferable if you need built-in API products, subscription keys, developer onboarding, API analytics, policy management, or a developer portal.

7. Reverse Proxy vs API Gateway in a Microservices Architecture

Consider a taxi-booking application with the following services:

User Service
Driver Service
Booking Service
Payment Service
Notification Service

Using a Reverse Proxy

Mobile App
    |
    v
Reverse Proxy
    |
    +-- /users     ------> User Service
    +-- /drivers   ------> Driver Service
    +-- /bookings  ------> Booking Service
    +-- /payments  ------> Payment Service

This approach provides a common network entry point and routes requests to the appropriate services.

Using an API Gateway

Mobile App
    |
    v
API Gateway
    |
    +-- Authenticate and authorize requests
    |
    +-- Apply rate limits and API policies
    |
    +-- Route requests to backend APIs
    |
    +-- Collect logs, metrics, and traces
    |
    +-- User Service
    +-- Driver Service
    +-- Booking Service
    +-- Payment Service

This approach adds centralized API policies to the routing layer. Business rules such as calculating a fare, assigning a driver, or processing a payment should normally remain in the appropriate application services rather than being placed in the gateway.

8. When Should You Use Each One?

Choose a Reverse Proxy When

You primarily need to route traffic to backend servers.
You need load balancing, TLS termination, or centralized ingress.
You want a lightweight traffic layer in front of web applications or internal services.
You already manage authentication and API policies elsewhere.

Example: Use Nginx, HAProxy, or YARP to route incoming web traffic to multiple application instances.

Choose an API Gateway When

You expose APIs to mobile apps, web applications, partners, or third parties.
You need centralized API authentication, authorization, and rate limiting.
You need API versioning, usage analytics, or request transformation.
You manage many APIs and need consistent policies across teams.
You need API products, subscriptions, or a developer portal.

Example: Use Azure API Management to publish and govern APIs for a mobile application that accesses user, booking, and payment services.

Can You Use Both?

Yes. A reverse proxy and an API gateway can coexist, but they should have clearly defined responsibilities.

Internet
   |
   v
Edge Reverse Proxy / Load Balancer
   |
   v
API Gateway
   |
   +-- User API
   +-- Booking API
   +-- Payment API

The edge reverse proxy can handle ingress traffic and load balancing, while the API gateway handles API-specific policies. However, avoid unnecessary layers that add latency, operational overhead, and duplicate responsibilities.

9. Final Summary

Question	Answer
What is a reverse proxy?	A server that forwards client requests to backend servers and returns their responses.
What is an API gateway?	An API entry point that routes requests and commonly enforces centralized API policies.
Is an API gateway a reverse proxy?	It commonly uses reverse-proxy functionality, but may provide additional API management capabilities.
Can YARP act as an API gateway?	Yes. YARP can be combined with ASP.NET Core middleware and other components to implement gateway behavior.
Which is better for API management?	A dedicated API gateway or API management platform is often preferable when centralized API policies and management features are required.

Interview answer: A reverse proxy primarily forwards and manages traffic between clients and backend servers. An API gateway builds on routing capabilities to expose and govern APIs through features such as authentication, authorization, rate limiting, versioning, and monitoring. Use a reverse proxy for traffic management and an API gateway when API-specific policies and management are important.

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Reverse Proxy vs API Gateway