The concept of a reverse proxy is widely used in distributed systems architecture. In this article, we’ll explore what a reverse proxy is, why it’s beneficial, and how to implement one using YARP Microsoft’s reverse proxy library.

What Is a Reverse Proxy?

A reverse proxy is a server that stands between clients and a single or multiple backend servers. In contrast to a traditional proxy, where the proxy does something on the client’s behalf, a reverse proxy takes the requests from clients and sends them to internal servers, and delivers the response to the requester. This configuration provides numerous benefits such as:

  • Routing: Directs requests to different backend servers based on parametric rules.
  • Load Balancing: Distributes incoming traffic across multiple servers, improving performance and scalability.
  • Security: Hides the details of internal servers, protecting them from unauthorized access and attacks.
  • Caching: Stores frequent responses to reduce the load on backend servers.
  • SSL Termination: Manages encrypted connections centrally, offloading the burden from backend servers.
  • Connection Abstraction and Decoupling: By terminating incoming client connections and establishing separate connections to backend servers, a reverse proxy allows for independent management of these connections.
  • Versioning: Different versions of an API can be supported using different URL mappings.

How a reverse proxy handles HTTP?

A reverse proxy acts as an intermediary between clients and back-end servers, managing HTTP traffic through various significant stages:

  • Request Handling: The reverse proxy accepts incoming client requests on defined ports and endpoints. On the receipt of a request, it closes the client connection, effectively decoupling the client from the back-end infrastructure.
  • Routing and Forwarding: Based on the routing rules defined in advance, the proxy chooses the appropriate backend server to handle the request. It can modify request paths and headers if necessary to comply with the requirements of the target server. The proxy sends the request to the selected server, usually utilizing connection pooling to ensure optimal performance.
  • Response Processing: After the request is processed by the backend server, it sends the response back to the reverse proxy. The proxy may further modify the response, such as modifying headers or changing content, before sending it to the client.​

This architecture offers advantages like load balancing, enhanced security, version control, and greater system flexibility.

Introducing YARP by Microsoft

YARP is an open-source library developed by Microsoft that allows you to create highly configurable and high-performance reverse proxies for ASP.NET Core. YARP is adaptable and can be easily integrated into .NET projects so that you can easily specify routing rules, destination management, and message transformations in a simple way.

Practical Example: Implementing a Reverse Proxy with YARP

  1. Install the YARP Package Add the YARP package to your project:
Install-Package Yarp.ReverseProxy
  1. Configure YARP in the Program.cs File Below is a minimal configuration example:
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var builder = WebApplication.CreateBuilder(args);

// Register YARP and load configuration from the app settings
builder.Services.AddReverseProxy()
    .LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"));

var app = builder.Build();

// Map YARP to handle routing based on the configuration
app.MapReverseProxy();

app.Run();
  1. Set Up Routing in appsettings.json Add a dedicated section for YARP to define routes and clusters:
{
  "ReverseProxy": {
    "Routes": {
      "route1": {
        "ClusterId": "cluster1",
        "Match": {
          "Path": "{**catch-all}"
        }
      }
    },
    "Clusters": {
      "cluster1": {
        "Destinations": {
          "destination1": {
            "Address": "https://destination.com/"
          }
        }
      }
    }
  }
}

In this example, all incoming requests are routed to https://destination.com/. You can further customize the configuration to handle more complex scenarios, such as multiple clusters, URL rewriting, or custom middleware.

Conclusion

Implementing a reverse proxy presents a number of benefits in security, scalability, and centralized traffic management. In YARP, Microsoft provides developers with a versatile and extensible solution that’s natively a part of today’s .NET applications.

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