JP3153129B2 - Server selection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for selecting a server computer (hereinafter simply referred to as "server") by a program on a client computer (hereinafter simply referred to as "client"), and more particularly to a server using a name server. Regarding the selection method.

[0002]

2. Description of the Related Art In a computer network environment in which a client computer and a server computer are connected to a network, it is widely practiced to install a plurality of servers that provide the same service for the purpose of load distribution and troubleshooting. .

[0003] Under such circumstances, service requests from clients to the servers are often concentrated on a small number of servers, and the responsiveness and performance of clients using servers with heavy loads may be reduced.

For this reason, it is necessary for the client and its program to transparently distribute the user load of the client evenly between the servers.

When a failure occurs in a server and the service from the server stops, it is necessary to select another normal server transparently for the client and its program.

Conventionally, as a server selection method in consideration of such circumstances, for example, a simple method of uniformly distributing clients assigned to each server in advance statically or a more practical technique disclosed in -9323
As described in Japanese Patent Laid-Open Publication No. 8 (1996) -2000, when a client requests a name server to acquire an Internet address of a server, the name server selects a server address with a low load in consideration of the load on the server and gives the client an address. A method of dynamically performing load balancing by notifying has been proposed.

[0007]

However, in the above-described conventional server selection method, the function of load distribution can be realized, but no consideration is given to the case where the designated server stops functioning due to a failure. In such a case, there is a problem that the client cannot receive the service from the server.

Incidentally, since the address of the server is usually stored in the memory of the client, even after the name server recognizes that the server has stopped functioning and updates the address list, the client thereafter receives the service from the server. Can not do.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-described problems, and it is possible to appropriately perform load distribution between servers and effectively avoid a failure even when a server stops functioning due to a failure. An object of the present invention is to provide a server selection method that can be used.

[0010]

In order to achieve the above-mentioned object, the present invention provides a server selection method in a client / server type computer network environment in which an address list specifying the order of servers to be selected is provided to a client. includes a name server to be passed, the client-side, the address resolution for dynamic link library an address of the query, and sends a probe packet to request the server operational status to each server according to the order of address list passed from the name server The address of the server that did not respond
There is provided a server selection method characterized in that a server is deleted from an address list .

Further, the present invention provides a server selection method in a computer network environment by a client / server method, comprising a name server for passing a metric to a client including a metric in an address list of a server to be selected. The order of the servers to be selected is determined based on the metric included in the address list passed from the name server by the dynamic link library for address resolution performing the inquiry, and the probe packet is transmitted to each server in accordance with the determined order. To check server operation status
Address of the server that did not respond
A server selection method is provided, which is characterized in that a server is deleted from a list .

As described above, according to the server selection method of the present invention, the order of the address list passed from the name server or the address list is included in the address list by the dynamic link library for address resolution that inquires the address on the client side. By trying to connect to each server in order according to the order determined based on the metric, even if the server selected by the name server stops functioning, it is possible to connect to the next best server and take measures against the failure.

According to the server selection method of the present invention,
Even if the program on the client is not modified, it can be dealt with only by replacing the dynamic link library for address resolution for finding the address corresponding to the name, and the transparency to the program on the client can be maintained.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, in an embodiment of the present invention, a client / server in which a client computer 200 and server computers (1) 300, (2) 400 and (3) 500 are connected to a computer network 600 Server computers (1) 300, (2) 400 and (3) 5 to be selected in a computer network environment according to the scheme
Name server computer 10 that passes an address list specifying the order of 00 to client computer 200
0 when the client program 24 operating on the client computer 200 attempts to access any of the server computers (1) 300, (2) 400 and (3) 500 that provide the same service. An address list that specifies the order of server computers that can be accessed from the name server computer 100 is acquired by the address solving dynamic link library 23 that inquires about addresses, and probe packets are transmitted to each server computer in accordance with the order of the address list. By confirming the operating status of the server computer, only the address of the operating server computer is stored in the client program 24.
To return.

[0016]

Next, in order to more specifically describe the above-described embodiment of the present invention, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention.

Referring to FIG. 1, in one embodiment of the present invention, a name server computer 100, a client computer 200, three server computers (1) 300,
(2) a server group consisting of 400 and (3) 500;
Is connected. In FIG. 1, only three server computers and one client computer are shown for convenience of illustration, but the present invention is not limited to this, and a plurality of server computers and client computers can of course be connected.

The name server computer 100 includes an input device 11 and an output device 12 for transmitting and receiving data via the computer network 600, a determination logic 13 for determining a priority order of a plurality of server computers according to a certain standard, and a server name. A conversion mechanism 14 for converting data into a corresponding address list, a writing means 15 for updating data in the storage device 17, a reading means 16 for reading data from the storage device 17, and a list of pairs of server names and addresses. And a storage device 17 for storing

The client computer 200 includes an input device 21 and an output device 22 for transmitting and receiving data via the computer network 600, a dynamic link library 23 for address resolution, and a client program 24.

Next, the operation of one embodiment of the present invention will be described. FIG. 2 is a flowchart showing the flow of processing by the address solving dynamic link library 23 shown in FIG.

Referring to FIGS. 1 and 2, a client program 24 running on a client computer 200 is used to provide a group of servers (server computers (1) 300, (2) 400 and (3) 500) that provide a uniform service. In order to obtain the correct address of the server computer, the dynamic link library for address resolution 2
Pass the server name to 3 and request processing to return the correct address.

At this time, the client computer 20
Dynamic link library 23 for address resolution of 0
Receives the server name from the client program 24 (step S1), and makes an inquiry about the address to the name server computer 100 via the output device 22 (step S2). The communication protocol at this time is known to those skilled in the art.

The input device 11 of the name server computer 100 receives the server name transmitted from the client computer 200 and passes it to the conversion mechanism 14. The storage device 17 of the name server computer 100 holds a list of pairs of server names and addresses. When the conversion is started, the conversion mechanism 14 generates an address list of data that matches the received server name. Reading means 16
, And returns the read address list to the client computer 200 via the output device 12.

The dynamic link library for address resolution 23 of the client computer 200 receives the address list via the input device 21 (step S3). According to the prior art, this address list is passed to the client program 24 as it is. In this embodiment, however, the address list is provided beforehand to confirm whether the server computer is actually performing the service. The probe packet is transmitted to the address indicated at the head of the address list (step S4). It should be noted that the probe packet includes the ICMP ECH
An O packet or a protocol defined between the server and the client in advance can be used.

Waiting for a response from the server computer of the destination of the probe packet for a certain period of time (step S5), and when a response is returned (step S6), it is regarded that the service of the server computer is running.
The value of the start address is returned to the client program 24 as an address corresponding to the requested server name (step S10).

On the other hand, if there is no response from the server computer (step S6), it is assumed that the service of the server computer has stopped, and the start address is removed from the address list (step S6).
7) If the next address remains (step S
8) Returning to step S4, the operation status of the service of the server computer corresponding to the address is continuously confirmed.

Thus, steps S4 to S8
If no response is received from the server computer corresponding to all the addresses on the address list (step S8), an error indicating that the address is unknown is returned to the client program 24, or the error processing is performed by the client. Entrust to the computer 24 and return any address in the address list (step S
9).

The name server computer 100 is provided with a determination logic 13 for determining the priority order of a plurality of server computers according to a certain standard.
The decision logic 13 uses a metric string
g) to each server computer to determine the preferred order of server computers. Here, the order of the server computers on the basis that the current load is smaller is adopted as the optimum order. Decision logic 13 launches a number of child processes, each of which sends a metric string to a particular server computer and receives a response from the server computer to which the metric string was sent. Decision logic 13
Determines the order in which the server computer should be preferred based on the received response, creates a list of pairs of server names and addresses, and writes the data in the storage device 17 by the writing means 15 while maintaining the preference order. Update.

As described above, according to the present embodiment, it is possible to realize dynamic load distribution and failure avoidance completely transparent to the client program 24.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, but includes various modified embodiments according to the principle of the present invention.

For example, instead of returning the ordered address list from the name server computer 100 to the client computer 200 as in the above-described embodiment, the address list including the metric is returned to the client computer 200, and the address resolution of the client computer 200 is resolved. The dynamic link library 23 may determine the priority order by itself based on the metric. In the case of such a change, the determination logic 13 of the name server computer 100 does not need to determine the priority order based on the metric, and only needs to add the metric to the address list and write it in the storage device 17. Has advantages.

Further, as in the above-described embodiment, the dynamic link library 23 for address resolution of the client computer 200 transmits the temporary address (the head address of the list or the An address not normally used) may be returned. That is,
By modifying the existing communication library and recognizing the necessity of confirming the operation status of the server computer by detecting the temporary address when the client program 24 actually establishes communication with this temporary address. Then, the operating status of the server computer is confirmed by the address solving dynamic link library 23 according to the same procedure as in the above-described embodiment. In addition, in the case of such a change, there is an advantage that a communication opening request packet for the service of the server computer can be used as the probe packet.

[0034]

As described above, according to the present invention,
A dynamic link library for client address resolution sends out probe packets to check the operating status of the server computer, enabling dynamic load distribution between servers and avoiding failures without modifying the client program. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a flow of processing by a dynamic link library for address resolution according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 input device 12 output device 13 decision logic 14 conversion mechanism 15 writing means 16 reading means 17 storage device 21 input device 22 output device 23 dynamic link library for address resolution 24 client program 100 name server computer 200 client computer 300 server computer 1 400 server Computer 2 500 Server computer 3 600 Computer network

Claims (3)

(57) [Claims] In a server selection method in a computer network environment by a client / server method, a name server for passing an address list designating an order of servers to be selected to a client is provided. Dynamic link library for solution
A probe packet is sent to each server in accordance with the order of the address list passed from the name server to check the operation status of the server, and to determine the address of the server that has not responded.
A server selection method for deleting from the address list . 2. A server selection method in a computer network environment based on a client / server method, comprising: a name server for passing a metric to a client including a metric in an address list of a server to be selected; The order of servers to be selected is determined by the dynamic link library for resolution based on the metric included in the address list passed from the name server, and a probe packet is sent to each server in accordance with the determined order to send a probe packet to each server. Check the operation status and there is no response
The server address of the server
Server Selection, characterized in that that. 3. When the client actually establishes communication with the server, the client calls the address resolution dynamic link library via a communication library, and a communication establishment request packet to the server is used as the probe packet. 3. The server selection method according to claim 1, wherein the operation status of the server is confirmed by sending the server.