How can I know when Kestrel has started listening?

Question

I need to notify systemd that my service has started up successfully, and a task it needs to run after startup requires that the server is already listening

Answer 1

• On .Net Core 1.x it is safe to just run IWebHost.Start() and assume that the server is initialized afterwards (instead of Run() that blocks the thread). Check the source.

  var host = new WebHostBuilder()
      .UseKestrel()
      (...)
      .Build();
  
  host.Start();
  

• If you are using .NET Core 2.0 Preview 1 (or later), the source is different, the synchronous method is not available anymore so you should await IWebHost.StartAsync() and assume everything is ready afterwards.