“An attempt was made to access a socket in a way forbidden by its access permissions” when accessing localhost from inside an Azure Function

Question

Disclaimer:

It's a cliche but it works on my machine(!)

Context:

Http Triggered Azure Function App Running on Windows With a "Free Tier" option.

Details:

I have an Azure Function App that host and runs a JAR file that spins up a Grizzly server which basically serves a JAVA app hosted in localhost:8080 The function app manages to start up the JAVA app by simply using. The JAVA app is called Open Trip Planner and it runs in a Grizzly server.

 Process.Start(javaPath, "<<JAR OPTIONS HERE>>");

• Up until here it works in both my machine and Azure.

Then I run a separate thread that checks the App has started:

                  while (true)
                  {
                      Thread.Sleep(10000);
                      try
                      {
                          var result = await client.GetAsync("http://localhost:8080"); 
// <-- The above fails in Azure but not in my local machine.
                      }
                      catch (Exception ex)
                      {
                          log.LogError(ex.Message);
                      }
                  }

The exception is: "“An attempt was made to access a socket in a way forbidden by its access permissions”

Exception Details:

Exception Type:

System.Net.Http.HttpRequestException

Message

An attempt was made to access a socket in a way forbidden by its access permissions

StackTrace

at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken) at System.Threading.Tasks.ValueTask1.get_Result() at System.Net.Http.HttpConnectionPool.CreateConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken) at System.Threading.Tasks.ValueTask1.get_Result() at System.Net.Http.HttpConnectionPool.WaitForCreatedConnectionAsync(ValueTask1 creationTask) at System.Threading.Tasks.ValueTask1.get_Result()
at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean doRequestAuth, CancellationToken cancellationToken)
at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts) at ScoreAddressFunction.ScoreAddress.<>c__DisplayClass3_0.<b__0>d.MoveNext() in /home/vsts/work/1/s/ScoreAddressFunction/ScoreAddressFunction/ScoreAddress.cs:line 85

However, it works if I change the URL to something like "https://www.google.com" which makes me think this is not caused by a limited number of available sockets as a read in other answers.

Question:

Is there something wrong -conceptually- with trying to access localhost (or 127.0.0.1) from inside an Azure Function App? Am I missing some technical / security restriction?

One of my concerns is that I am facing this issue from a wrong conceptual point of view. However, the process I run needs A LOT of memory and having it working on an Azure Function App for the time I need it would be awesome otherwise it will be very expensive.