Blazor Interactive Server Deployed on ACA delivers 404 on websockets

[rbuergi]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have a blazor interactive server which is integrated in Aspire 9.1. I deploy it to Azure Container Apps.

In the deployed setup, when reloading the page a number of times, it randomly fails about every other time with

blazor.web.js:1  [2025-03-18T00:38:15.068Z] Error: Failed to start the transport 'WebSockets': 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.

running it locally on docker, I don't observe this behavior. Is this a known problem? Is this ACA specific? Anything I can do to make this go away?

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

No response

Anything else?

No response

[javiercn]

@rbuergi thanks for contacting us.

Have you enabled websockets on Azure Container Apps>

[rbuergi]

thanks, @javiercn for answering so quickly. I have searched for how to do this, and I don't find any corresponding setting. When asking copilot, I was told that I need to configure health checks (which I have, according to aspire docs). On the ingress page, I have selected http/1 and unchecked session affinity. Is this the recommended setting? Where can I explicitly enable websockets?

Also, please note that it basically works, it just has problems connecting. This is especially annoying since people click on links and report that the website is not working. When you reload, sometimes it works and sometimes not. It looks like it is not fast enough reacting. Is there some timeout I could set?

[javiercn]

@rbuergi thanks for the additional details.

can you check your setting s on the Ingress tab?

[rbuergi]

Hi @javiercn as mentioned above, i had

On the ingress page, I have selected http/1 and unchecked session affinity.

I have now checked session affinity to see what's happening (even though I have only one replica deployed), and it seems to cure the problem. I know that this flag would be required with more than one replica, but it is unclear to me why I need it with one.

Generally, it would help to have better documentation on deployment scenarios, especially to ACA. I have worked with Azure since it has existed and am quite knowledgeable in terms of infra and deployment, but I was struggling a lot to make things work stably on ACA. Maybe it would be worth creating deployable solutions in aspire-samples; even though there are blazor examples in there, they usually don't cover deployment scenarios.

Anyway, thanks a lot for your help. I am closing this ticket.