GenHTTP

Legacy Migration

Runs on your machine

Replaces a legacy app step by step with a reverse proxy, redirects and new endpoints.

Reverse Proxies Documentation Redirects Documentation GenHTTP.Modules.ReverseProxy Package on NuGet GenHTTP.Modules.Redirects Package on NuGet

Replaces an old web application step by step instead of all at once. GenHTTP runs in front of the legacy application: new endpoints and pages are served by GenHTTP, moved pages are redirected, and everything else is passed on to the legacy application by a reverse proxy.

The layout tries its own routes first, so /api/v2/ and /contact are new, /contact.php redirects permanently (search engines learn the new address), and any other path - such as /login.php - still reaches the legacy application on port 5000. Move one route at a time until the proxy can go.

Runs on your machine only. It forwards requests to a legacy application running on your machine.

To run it, create a console app (dotnet new console), add GenHTTP (dotnet add package GenHTTP.Full), replace Program.cs with the code below and start it with dotnet run - it answers at http://localhost:8080/.

Program.cs35 lines 
using GenHTTP.Engine.Internal;

using GenHTTP.Api.Protocol;

using GenHTTP.Modules.Functional;
using GenHTTP.Modules.IO;
using GenHTTP.Modules.Layouting;
using GenHTTP.Modules.Practices;
using GenHTTP.Modules.Redirects;
using GenHTTP.Modules.ReverseProxy;

var newApi = Inline.Create()
                   .Get("status", () => new Status(true));

var contact = Content.From(Resource.FromString("<h1>Contact us</h1>").Type(ContentType.TextHtml));

// the legacy application, running on port 5000
var legacy = Proxy.Create()
                  .Upstream("http://localhost:5000/")
                  .ConnectTimeout(TimeSpan.FromSeconds(5))
                  .ReadTimeout(TimeSpan.FromSeconds(30));

var app = Layout.Create()
                .Add("api/v2", newApi) // GET /api/v2/status
                .Add("contact", contact)
                .Add("contact.php", Redirect.To("/contact")) // permanent, so search engines learn the new URL
                .Add("shop", Redirect.To("https://shop.example.com/", temporary: true))
                .Add(legacy); // everything else, e.g. GET /login.php

await Host.Create()
          .Handler(app)
          .Defaults()
          .RunAsync();

public record Status(bool Healthy);

Try it

With the sample running on your machine:

  1. Call the rewritten API

    curl -i http://localhost:8080/api/v2/status

  2. Open a page that has moved

    301 to the rewritten page

    curl -i http://localhost:8080/contact.php

  3. Open a page of the legacy app

    502, unless the legacy app runs on port 5000

    curl -i http://localhost:8080/login.php