In this place, there's information on changes to Core as follows.
public void Configure(IApplicationBuilder app, ILoggerFactory loggerfactory)
// Remove call to app.UseIISPlatformHandler(); This is handled by UseIIS in Main.
// Remove call to app.UseForwardedHeaders(); This is handled by UseIIS in Main.
public static void Main(string args)
var host = new WebHostBuilder()
// Replaces call to UseIISPlatformHandlerUrl()
The issue is rather old and some things have changed since then. You are on the right track, though.
UseIISPlatformHandler call indeed moved from Startup to Program start and has been renamed to