We have an Azure application where Functions Apps (Backend) which talks to Azure SQL Server and is front-ended thru API Management service (and we have App gateway thru which the APIs are called). Application works fine as such but as soon as we are doing load testing with 50 to 100 concurrent users we see some of the requests with (ClientConnectionFailure: at transfer-response).
[{"severityLevel":"Error","outerId":"0","message":"Client connection was unexpectedly closed.","type":"ClientConnectionFailure","id":"0","parsedStack":[{"method":"transfer-response","level":0,"line":0}]}]
I have checked the trace table on Application Insights and I dont see any failure so I am not sure if this is causing from the JMeter load test client that the connection is getting dropped before the response is coming from Server under load.
Anyone face issue like this and found a fix? We are running with Premium Service plan and as such dont see major issues with our Service or SQL calls.
Appreciate your help.
Thank you,
Following my initial thread reporting this issue, and besides the fact that the comments and response are talking about the timeout in the backend, there was no evidence that the backend was performing poorly. I check the logs and as I mentioned in the original thread, the backend and the client apps had low response times (<1min) to cause the timeout. So I started to explore a different option, in this case, the number of requests performed at the same time to the APIM, and I would say if you perform a significant number of requests at the same time, some of them will start to queue, and depending on how long they will be queued, potentially the client will start to timeout. So as far as I remember, I throttled the scalability of the azure functions to do not scale massively. Or if you do not want to go in that direction, you can try the Premium Plan on Azure Functions