Forum Discussion
NimbostratusAPM webtop – problem with websockets for Serverside Blazor app
Dear community,
We have a web application built with Blazor server side rendering that utilizes SignalR (websockets) and runs on a Windows server with IIS (i.e. not web assembly).
Virtual sever: the site runs as intended!
Webtop + virtual sever: The site will render and SSO works, but any page using SignalR will loose interactivity as the websocket handshake times out.
We have tried to disable websockets on the server which makes SignalR use long polling as a fallback. The web browser displays a different error message but behaves the same otherwise (have not dug deeper as we intend to use websockets in production).
I would greatly appreciate any guidance on what to do!
This is the log from the blazor web app (behind webtop + virtual server):
2025-09-18 16:50:26 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubProtocolResolver Registered SignalR Protocol: json, implemented by Microsoft.AspNetCore.SignalR.Protocol.JsonHubProtocol.
2025-09-18 16:50:26 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubProtocolResolver Registered SignalR Protocol: blazorpack, implemented by Microsoft.AspNetCore.Components.Server.BlazorPack.BlazorPackHubProtocol.
2025-09-18 16:50:27 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionManager New connection XQNqGM4oGkm0P1v4NECJ9g created.
2025-09-18 16:50:27 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionDispatcher Sending negotiation response.
2025-09-18 16:50:27 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionDispatcher Establishing new connection.
2025-09-18 16:50:27 Debug Microsoft.AspNetCore.SignalR.HubConnectionHandler OnConnectedAsync started.
2025-09-18 16:50:27 Debug Microsoft.AspNetCore.Http.Connections.Internal.Transports.WebSocketsTransport Socket opened using Sub-Protocol: '(null)'.
2025-09-18 16:50:42 Debug Microsoft.AspNetCore.SignalR.HubConnectionContext Handshake was canceled.
2025-09-18 16:50:42 Debug Microsoft.AspNetCore.Http.Connections.Internal.Transports.WebSocketsTransport Waiting for the client to close the socket.
2025-09-18 16:50:42 Debug Microsoft.AspNetCore.Http.Connections.Internal.Transports.WebSocketsTransport Socket closed.
2025-09-18 16:50:42 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionManager Removing connection xVt0cL2a0gpMOiJROyJxhw from the list of connections.
This is the log from the same blazor web app when it works as intended
2025-09-18 17:29:31 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubProtocolResolver Registered SignalR Protocol: json, implemented by Microsoft.AspNetCore.SignalR.Protocol.JsonHubProtocol.
2025-09-18 17:29:31 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubProtocolResolver Registered SignalR Protocol: blazorpack, implemented by Microsoft.AspNetCore.Components.Server.BlazorPack.BlazorPackHubProtocol.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionManager New connection c0CR_c-7xa0QydeddE5HcA created.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.Http.Connections.Internal.HttpConnectionDispatcher Sending negotiation response.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.HubConnectionHandler OnConnectedAsync started.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.Http.Connections.Internal.Transports.WebSocketsTransport Socket opened using Sub-Protocol: '(null)'.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubProtocolResolver Found protocol implementation for requested protocol: blazorpack.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.HubConnectionContext Completed connection handshake. Using HubProtocol 'blazorpack'.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubDispatcher Received hub invocation: InvocationMessage { InvocationId: "0", Target: "StartCircuit", Arguments: [ https://testsite.com/, https://testsite.com/counter, [], CfD...m ], StreamIds: [ ] }.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubDispatcher Received hub invocation: InvocationMessage { InvocationId: "", Target: "EndInvokeJSFromDotNet", Arguments: [ 2, True, [2,true,null] ], StreamIds: [ ] }.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubDispatcher Received hub invocation: InvocationMessage { InvocationId: "", Target: "UpdateRootComponents", Arguments: [ {"batchId":1,"operations":[{"type":"add","ssrComponentId":1,"marker":{"type":"server","prerenderId":"80...9c8","key":{"locationHash":"....","formattedComponentKey":""},"sequence":0,"descriptor":".... ], StreamIds: [ ] }.
2025-09-18 17:29:37 Debug Microsoft.AspNetCore.SignalR.Internal.DefaultHubDispatcher Received hub invocation: InvocationMessage { InvocationId: "", Target: "OnRenderCompleted", Arguments: [ 2, ], StreamIds: [ ] }.
This is the output in the web browser console when accessing the site via (webtop + virtual server):
2025-09-18T14:50:28.565Z Information: Normalizing '_blazor' to 'https://testsite.com/f5-w-68747470733a2f2f6d6139392e6d6963726f2d746573742e696e747261$$/f5-h-$$/_blazor'. blazor.web.js?F5CH=J:1
2025-09-18T14:50:28.609Z Information: WebSocket connected to wss://testsite.com/f5-w-68747470733a2f2f6d6139392e6d6963726f2d746573742e696e747261$$/f5-h-$$/_blazor?id=xVt0cL2a0gpMOiJROyJxhw. blazor.web.js?F5CH=J:1
2025-09-18T14:50:43.620Z Error: Connection disconnected with error 'Error: Server returned handshake error: Handshake was canceled.'. blazor.web.js?F5CH=J:1
2025-09-18T14:50:43.620Z Error: Error: Server returned handshake error: Handshake was canceled. blazor.web.js?F5CH=J:1
2025-09-18T14:50:43.620Z Error: Failed to start the circuit. blazor.web.js?F5CH=J:1
3 Replies
- Jeffrey_Granier
Employee
Hi Olof,
Have you tried to add a websocket profile to the VS ? For client side websocket profile you might need to toggle mask payload:
select Remask (default; unmasks client frames for proxying/inspection, then remasks for the backend).
Use Preserve if no inspection is needed (performance with binary BlazorPack payloads in SignalR) or if remasking causes issues.
Also consider extending the handshake timeout on the Blazer app config. Best to eliminate a timeout value maybe set for 45 or 60 seconds...Re-test and see if the handshake timeout is still appearing. I think the underlying issue is a proxying/websocket framing issue.
OlofHi Jeffrey,
Thank you for the response!
We have tried the WebSocket profile now (with and without preserve), but unfortunately the handshake still times out.
I adjusted the handshake timeout in the Blazor app, but it only delays the error message.
A colleague found an article that hinted it might be an issue with javascript versions: https://my.f5.com/manage/s/article/K15142093
We have written very few javascripts for the app and tried deactivating them completely without effect. But Blazor generates a “blazor.web.js” script that is served to the client.
I haven’t found any clear information about the javascript version in that script, but an issue on github had a complaint about “high version syntax”. That issue regarded .NET9 and we use .NET8, but the issue was resolved with a comment that Microsoft only supports the latest web browsers: https://github.com/dotnet/aspnetcore/issues/59090
Could javascript version be the issue?
- Jeffrey_Granier
Hi Olof,
JS version compatibility seems to be a problem on the GH issues your shared. Have you looked at testing this irule workaround here ---> Correcting a portal access rewrite failure when rewriting a URL this was mentioned in this KB article: BIG-IP APM Portal Access - JavaScript ES6/ES7/ES8+ compatibility
