<p>I am trying to run .net core application with Azure SignalR services(free tier). The .net core app is deployed in Azure Kubernetes Service. I have an Angular frontend app that tries to connect to the WebSocket. Below are my configurations in Program.cs file:</p>
<pre><code>    services.AddCors(options =&gt; options.AddPolicy(&quot;testing&quot;, builder =&gt;
    {
        builder.WithOrigins(&quot;https://somebackendserver.com&quot;);
        builder.AllowCredentials();
        builder.AllowAnyHeader();
        builder.AllowAnyMethod();
    })); 
    services.AddSignalR(options =&gt;
    {
        options.EnableDetailedErrors = true;
    }).AddAzureSignalR(connectionStringSignalR);


app.UseCors(&quot;testing&quot;);
app.UseEndpoints(configure =&gt;
{
    configure.MapHub&lt;GenerationNotificationHub&gt;(&quot;/hub&quot;);
});
</code></pre>
<p>This is my Angular side code to create a connection:</p>
<pre><code>public createConnection = (): void =&gt; {
    this.hubConnection = new signalR.HubConnectionBuilder()
      .configureLogging(signalR.LogLevel.Error)
      .withUrl(`https://somebackendserver.com/hub`,
        {
          accessTokenFactory: () =&gt; this.sessionService.get(SignalrNotificationService.accessTokenStorageKey),
          transport: signalR.HttpTransportType.WebSockets,
          skipNegotiation: true
        })
      .withAutomaticReconnect()
      .build();

    this.hubConnection.start().then().catch();
  }
</code></pre>
<p>When the solutions are deployed in AKS I get the following error in browser console window:</p>
<blockquote>
<p>Error: Failed to start the connection: Error: WebSocket failed to
connect. The connection could not be found on the server, either the
endpoint may not be a SignalR endpoint, the connection ID is not
present on the server, or there is a proxy blocking WebSockets. If you
have multiple servers check that sticky sessions are enabled.</p>
</blockquote>
<p>This is the server-side error log</p>
<blockquote>
<p>Failed to connect to
'(Primary)https://xxx.service.signalr.net(hub=GenerationNotificationHub)',
will retry after the back off period. Error detail: Unable to connect
to the remote server.  Received an unexpected EOF or 0 bytes from the
transport stream.. Id: 958c67ab-1e91-4983-83ad-bfaf02bc48da</p>
</blockquote>
<p>And this is the Postman error when I try to connect to the WebSocket:</p>
<blockquote>
<p>Status Code: 503 WebSocket request made to a site where WebSockets are
disabled. Request Headers Sec-WebSocket-Version: 13 Sec-WebSocket-Key:
AjiVAXGSpcYCbiGbftHbcg== Connection: Upgrade Upgrade: websocket
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits
Host: somebackendserver.com Response Headers Content-Length: 27
Content-Type: text/html Date: Mon, 19 Sep 2022 13:44:16 GMT Server:
Microsoft-IIS/10.0</p>
</blockquote>
<p>The application works fine when I try to run it on localhost but something seems off when I deploy it as Kubernetes service in Azure.</p>
<p>EDIT: We have a Kong API Gateway for managing our API Gateway services, and I am suspecting it is somehow blocking SignalR websocket network connections. I keep getting this CORS error</p>
<blockquote>
<p>Access to fetch at &gt;'https://api.XXX.dev.XXXXXX.com/hub/generation/negotiate?negotiateVersion=1' from origin 'https://XXXX.dev.XXXXXX.com' has been &gt;blocked by CORS policy:
Response to preflight request doesn't pass access control check: The 'Access-Control-Allow-Origin' header has a value &gt;'https://portal.api.dev.XXXX.com' that is not equal to the supplied &gt;origin. Have the server send the header with a valid value, or, if an opaque response serves your needs, set the request's mode to 'no-cors' &gt;to fetch the resource with CORS disabled.</p>
</blockquote>

Purushottam.Prasad
<p>I was able to figure out what went wrong here. We are using Kong API gateway 2.7.1 for our organization. This version of Kong does not support WS/WSS protocol. This explains the errors like:</p>
<blockquote>
<p>Status Code: 503 WebSocket request made to a site where WebSockets are
disabled.</p>
</blockquote>
<p>Or</p>
<blockquote>
<p>Error: WebSocket failed to connect. The connection could not be found
on the server, either the endpoint may not be a SignalR endpoint, the
connection ID is not present on the server, or there is a proxy
blocking WebSockets</p>
</blockquote>
<p>Another clue was that SignalR WebSockets was working on my local machine but not on the Cloud.</p>
<p>From Kong 3.0 Enterprise onwards, we have WebSocket support.
I hope this helps.</p>
