A relay control apparatus is arranged between clients and a CoD system.
The relay control apparatus accepts process requests from the clients and
stores the process requests. If the CoD system is installing a server in
addition to existing servers, the relay control apparatus provides a
control so that requests unprocessable with the existing servers are not
passed to the CoD system until the installation of the server is
completed. When the installation of the server is completed, servers that
can process, within a predetermined period, a volume of requests at that
time and a volume of requests retained by that time are secured.