VNET intermittent connection problem between Function App and Docker Instance - "No connection could be made because the target machine actively refused it"

Question

I'm running an Azure dot net function app and a docker instance in an Azure VNET.

The docker instance has a private IP of 10.1.0.4 and is running AVclam on 3310 but the function app fails 9 times out of 10 with the following error,
"No connection could be made because the target machine actively refused it".

I've changed the function app to use

  var clam = new TcpClient(AddressFamily.InterNetwork);

but this has had no effect. I'm running out of things to try, any suggestions on how to discover the problem and make this connection reliable?

Thanks

Answer 1

After clutching at straws and trying a number of things I managed to get this working successfully in the VNET. It turned out to be a problem with the docker image. While it seemed to work pretty reliably outside the VNET it did not work reliably inside the VNET. After replacing the docker image with a smaller AVClam image its now working reliably, without fail inside the VNET.