4428 - Expected behavior when the Traffic Manager sends a request to a backend server and the server closes the TCP connection with a FIN response without sending any HTTP response prior to it.

This article describes the expected behavior when a backend server closes the TCP connection with a FIN response without sending an HTTP response prior to it.

 

If the Traffic Manager sends a backend server a request, and the backend server closes the TCP connection with a FIN response without any HTTP response in the packet, then this is an example of a request failure.

This response is not logged into the system but the Traffic Manager reacts in the following manner: 

• Chooses a new backend node. (This is true if the request is idempotent* and is configured as Catalogs > Persistence > {your persistence class} > Basic Settings > failuremode to allows that).
• Deletes the session from a persistence class, so that the new connection will not go the same backend host.  (This is true if Catalogs > Persistence > {your persistence class} > Basic Settings > delete is set to Yes).

*Idempotent request is a request that is safe to resend.  All HTTP GET requests are idempotent unless marked otherwise with traffic script rules.

The default settings may be a problem with backend servers that close TCP connections without any HTTP response.  To prevent this, configure the backend server to send an HTTP response prior to sending the FIN response. 

If this is not an option, set "failuremode" to "Close the connection" and "delete" to "Yes". This will insure that the request from the existing session would not reach an unintended backend server.