Connection to signalR from Azure function fails with 403 (Forbidden) several times a day for 5 minutes, and then works again

Question

As titel, several times a day our connection to singalR from the azure function fails with a 403 forbidden error. After 5 minutes the connection recovers.

Full Exception :
 Exception while executing function
 /Functions.OrderToSignalR ---> Microsoft.Azure.SignalR.Common.AzureSignalRRuntimeException 
 /Azure SignalR service runtime error. Request Uri
 /https://[***].service.signalr.net/api/hubs/orders/:send?api-version=2022-06-01 ---> System.Net.Http.HttpRequestException 
 /Response status code does not indicate success
 /403 (Forbidden)
   End of inner exception

These calls typical start with a Invoke DefaultAzureCredential.GetToken, ManagedIdentityCredential.GetToken and then a post to [**].service.signalr.net

POST /api/hubs/orders/:send that fails with a 403. These calls repeat 6 times because of the servicebus retry.

Outside the 5 minute window where the calls fails, everything works normal.

Answer 1

@Dorus Peelen ,

Thanks for reaching out. If you're running into a 403 Forbidden error when connecting to SignalR from your Azure Function, a few things might be causing it:

• SAS Token Issues: If you're using a SAS token, make sure it's not expired when the client tries to use it. Avoid setting a start time for immediate use, and give it a reasonable expiry time.
• Authorization Problems: Your function might not have the right permissions to access SignalR. Check if the managed identity or credentials have the necessary access.
• Too Many Requests: If the service is under heavy load, it might temporarily block new connections. Keep an eye on usage and add some retry logic with a delay.
• Network Glitches: Sometimes, temporary network issues can cause connection failures. Make sure your function is set up to handle them.
• CORS Settings: If your function is running from a different origin, double-check that CORS settings allow requests from it.

Since the connection starts working again after about five minutes, it could be a temporary issue or some rate limiting in action. Adding retry logic in your function should help deal with these hiccups.

References:

• Troubleshoot connection errors
• Troubleshooting guide for Azure SignalR Service common issues
• Request throttling problems and HTTP 403 - Forbidden issues

Hope this helps. Do let us know if you have any further queries.

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