How to get the request URL on application startup

Sadly you are unable to retrieve the hosting URL of your application since that bit is controlled by IIS/WebListener etc. and doesn't flow through to the application directly.

Now a nice alternative is to provide each of your servers with an ASPNET_ENV environment variable to then separate your logic. Here's some examples on how to use it:

Startup.cs:

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        // Will only get called if there's no method that is named Configure{ASPNET_ENV}.
    }

    public void ConfigureDev(IApplicationBuilder app)
    {
        // Will get called when ASPNET_ENV=Dev
    }
}

---

Here's another example when ASPNET_ENV=Dev and we want to do class separation instead of method separation:

Startup.cs:

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        // Wont get called.
    }

    public void ConfigureDev(IApplicationBuilder app)
    {
        // Wont get called
    }
}

StartupDev.cs

public class StartupDev // Note the "Dev" suffix
{
    public void Configure(IApplicationBuilder app)
    {
        // Would only get called if ConfigureDev didn't exist.
    }

    public void ConfigureDev(IApplicationBuilder app)
    {
        // Will get called.
    }
}

Hope this helps.

This won't give you the domain but may help if you're just running on a port and need access to that:

        var url = app.ServerFeatures.Get<Microsoft.AspNetCore.Hosting.Server.Features.IServerAddressesFeature>().Addresses.Single();

Not sure what happens if you have multiple addresses bound.