Load-balancing device and computer-readable recording medium in which load-balancing program is recorded

A computer-readable recording medium storing a load-balancing program which is executed by a computer and makes the computer realize a load-balancing device for distributing request messages from clients among servers so as to balance loads imposed on the servers, and delivering ones of the request messages related to each other to an identical one of the servers so as to guarantee uniqueness, said load-balancing device comprises:

• a first specification-information detection unit which detects whether or not first specification information uniquely specifying a first destination server of a first request message sent from one of the clients to one of the servers is inserted in a predetermined area, other than a source-address area, of a response message responding to the first request message, when said load-balancing device receives the response message from the one of the servers;
• a specification-information insertion unit which detects a source server of said response message, designates the source server as said first destination server, generates second specification information uniquely specifying the first destination server, inserts the second specification information into the response message, and sends the response message to said one of the clients, when said first specification-information detection unit detects that said first specification information is not inserted in the first response message;
• a second specification-information detection unit which detects whether or not third specification information uniquely specifying a second destination server of a second request message is inserted in the second request message when said load-balancing device receives the second request message from said one of the clients, where the one of the clients stores said first or second specification information inserted in said response message, and inserts the third specification information in the second request message when it is necessary to guarantee the uniqueness;
• and
• a destination determination unit which determines the second destination server of said second request message in accordance with a predetermined rule when said second specification-information detection unit detects that the third specification information is not inserted in the second request message, determines said second destination server on the basis of the third specification information when said second specification-information detection unit detects that the third specification information is inserted in the second request message, and sends the second request message to the second destination server.