API Gateway Overview

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Introduction

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Architecture

Client → YARP API Gateway → Backend Microservices
                           ├─> Catalog Service
                           ├─> Basket Service
                           └─> Ordering Service

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Key Features

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Reverse Proxy Capabilities

• Dynamic Routing: Routes requests to different microservices based on URL paths
• Path Transformation: Strips service prefixes from URLs before forwarding
• Load Balancing: Distributes traffic across multiple service instances
• Rate Limiting: Protects services from excessive requests

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Technology Stack

• YARP Version: 2.1.0
• .NET Version: 8.0
• Configuration: JSON-based configuration in appsettings.json
• Rate Limiting: Built-in ASP.NET Core rate limiting middleware

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Project Structure

YarpApiGateway/
├── Program.cs                    # Application entry point and service configuration
├── YarpApiGateway.csproj        # Project file with YARP dependency
├── appsettings.json             # Production configuration (Docker)
├── appsettings.Local.json       # Local development configuration
├── appsettings.Development.json # Development environment settings
└── Dockerfile                   # Container image definition

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Service Configuration

using Microsoft.AspNetCore.RateLimiting;

var builder = WebApplication.CreateBuilder(args);

// Add YARP reverse proxy
builder.Services.AddReverseProxy()
    .LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"));

// Add rate limiting
builder.Services.AddRateLimiter(rateLimiterOptions =>
{
    rateLimiterOptions.AddFixedWindowLimiter("fixed", options =>
    {
        options.Window = TimeSpan.FromSeconds(10);
        options.PermitLimit = 5;
    });
});

var app = builder.Build();

app.UseRateLimiter();
app.MapReverseProxy();

app.Run();

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Supported Microservices

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Request Flow Example

1. Client Request: GET http://gateway:8080/catalog-service/api/v1/products
2. Route Matching: Gateway matches the /catalog-service/{**catch-all} pattern
3. Path Transformation: Strips /catalog-service prefix → /api/v1/products
4. Forwarding: Sends request to http://catalog.api:8080/api/v1/products
5. Response: Gateway returns the catalog service response to the client

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Deployment

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Docker Deployment

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
USER app
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

• 8080: HTTP endpoint
• 8081: HTTPS endpoint (optional)

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Local Development

• Catalog: http://localhost:6000
• Basket: http://localhost:6001
• Ordering: http://localhost:6003

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Configuration Environments

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Production (Docker)

• catalog.api:8080
• basket.api:8080
• ordering.api:8080

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Local Development

• localhost:6000 → Catalog
• localhost:6001 → Basket
• localhost:6003 → Ordering

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NuGet Dependencies

<PackageReference Include="Yarp.ReverseProxy" Version="2.1.0" />

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Benefits of YARP

1. Performance: Built on ASP.NET Core for high throughput
2. Flexibility: Configuration-driven with programmatic customization options
3. Simplicity: Minimal code required for basic reverse proxy functionality
4. Integration: Seamless integration with ASP.NET Core middleware
5. Maintainability: No need for external proxy software (Nginx, Envoy, etc.)

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Next Steps

• YARP Configuration - Detailed configuration reference
• Rate Limiting - Request throttling configuration
• Routing - Route matching and path transformation