US Patent 11283720 Methods and systems for accelerated health monitoring for load balancers

A network appliance can maintain an active set indicating active backends for a load balanced network service. To monitor the health of the backends, the network appliance can transmit a network packet to a backend that is one of the active backends in the active set and can receive a response packet responsive to the network packet. An invariant hash can be calculated from the response packet using fields that are the same when the response is a normal response (e.g. not an error response) from a healthy backend. If the packet indicates an error or is otherwise indicative of a problem, the network appliance can determine, using the invariant hash, that the response packet does not match an expected result associated with the backend. Based on the error, the number of network packets resulting in errors, etc., the backend can be removed from the active set.