The prioritized list of servers that are specified in a configuration file (i.e. primary server and backup servers) contain sufficient information to determine what to do when there is a failure of communication between servers, or between servers and clients. (A failure could be due to a malfunction of the communications medium, or of the computer hardware.)
There may, however, be good reason to be able to inform RPC Manager of the health of a service. Typically, this will be where a service has to communicate to, or employ, some third-party equipment. The service will need to indicate that it is, or is not, capable of performing the functions for which it was designed. A driver may typically use this facility to show its ability to communicate with a PLC.
This is achieved by setting or clearing the Alternate status of the service. RPC Manager monitors the Alternate setting to determine the most suitable service instance for the service. The rules by which server status is determined are described in Server Evaluation Rules.