Electrical computers and digital processing systems: multicomput – Distributed data processing – Client/server
Reexamination Certificate
2000-07-28
2004-04-20
Barot, Bharat (Department: 2155)
Electrical computers and digital processing systems: multicomput
Distributed data processing
Client/server
C709S217000, C709S219000, C709S224000, C709S229000, C709S235000, C709S238000, C718S105000, C370S237000
Reexamination Certificate
active
06725253
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a load balancing apparatus which balances the load of servers in a client/server system. More particularly, this invention relates to the load balancing system which prevents service from stopping in the event of a disaster.
BACKGROUND OF THE INVENTION
Recently, a load balancing technique f or preventing load concentration in a single server is used in large-scale networks of which the internet is a representative example. According to this technique, multiple servers are provided on a server side which receives a great number of accesses, and the multiple servers function as one server for a client.
This load balancing technique reduces the load on one server by balancing the access from the client among multiple servers. Therefore, in the load balancing technique, accesses are received from the client and are sorted as far as is possible to one of the multiple servers which has a low load and is located near the client. This is important in increasing the efficiency of the network.
FIG. 18
shows one example of a constitution of a conventional network system. In the network system shown in
FIG. 18
, a round robin method is used as a load balancing method in a DNS (Domain Name System) server. This round robin method handles an access by using domain names explained later, and balances the load by using IP addresses of multiple servers in sequence when converting the domain names to IP (Internet Protocol) addresses.
In
FIG. 18
, an LAN (Local Area Network)/WAN (Wide Area Network)
1
and an LAN/WAN
4
comprise large-scale networks for carrying out data communication between multiple computers, which are physically separated, by means of internet working. For example, the LAN/WAN
1
and
4
comprise an internet.
A network which satisfies the following conditions is appropriate as the above-mentioned internet.
(1) The computer network has a communications protocol (communications connection sequence) termed a TCP/IP (Transmission Control Protocol/Internet Protocol) mounted therein.
(2) The computer network is connected to one worldwide network configured around several basic networks.
Each protocol TCP and UDP (User Datagram Protocol) in the fourth layer (transport layer) of an OSI (Open System Interconnection) reference model is defined to create the TCP/IP. A characteristic of the TCP is to send reliable data communications (transmissions). That is, regular data communication is ensured by maintaining the reliability of the communications path from the start of the communication to the end of the communication, and by detecting and correcting errors.
The above-mentioned TCP has a connection-type server format for maintaining reliability. In contrast, the UDP is a data transmission protocol termed a connectionless-type for increasing the processing speed, and does not perform response confirmation or sequential adjustments of data received along different communications paths in the network in order to increase reliability.
The client
2
is provided on the client (user) side, and is connected to the LAN/WAN
1
. The client
2
comprises a computer end terminal for requesting service from a server
6
(and a server
7
) explained later via the LAN/WAN
1
and the LAN/WAN
4
. A client-side DNS server
3
realizes internet standard DNS and connects to the LAN/WAN
1
.
The DNS will be explained in detail. In the internet, IP addresses are used to identify the end terminals as described above. However, since an IP address comprises a combination of numbers expressed in four octets (32 bits), it is extremely difficult for a person to memorize. Accordingly, domain names (name space) which can be easily memorized by a person are appended to each end terminal as identifiers.
The DNS is a system for managing the relationship between the domain names and the IP addresses, and supplying an IP address in response to an inquiry from the client
2
relating to a domain name. The client-side DNS server
3
is an apparatus for realizing the above-mentioned DNS, and is positioned as a local DNS server for the client
2
.
The server
6
is provided on the service supplier side and connects to the LAN/WAN
4
. The server
6
comprises a computer terminal for supplying service to the client
2
in accordance with a service request therefrom. The server
7
is similarly provided on the service supplier side as the server
6
and connects to the LAN/WAN
4
. The server
7
comprises a computer terminal for supplying service to the client
2
in accordance with a service request therefrom. The server
6
and the server
7
are provided in physically different places. Therefore, the distances between the servers
6
and
7
and the client
2
(the client-side DNS server
3
) are different.
From the point of view of the client
2
, the servers
6
and
7
function as a single server. A single domain name (hereinafter termed representative domain name) is appended representatively to the servers
6
and
7
. In addition, IP addresses are appended to the servers
6
and
7
. That is, multiple IP addresses are registered to one domain name in this case, so that the client
2
can access either one of the servers
6
and
7
by accessing one domain name.
That is, the servers
6
and
7
form one virtual server which is expressed by the representative domain name, and the client
2
accesses the representative domain name of this virtual server. One representative domain name is appended to the servers
6
and
7
, and the client
2
can access either one of the servers
6
and
7
, in order to balance the load as described above. This load balancing will be explained later.
A server-side DNS server
5
functions as a DNS server in the same way as the client-side DNS server
3
, and is provided as a higher-level apparatus of the client-side DNS server
3
. That is, the server-side DNS server
5
responds to inquiries relating to IP addresses from the client-side DNS server
3
.
The server-side DNS server
5
is responsible for the servers
6
and
7
, and when an inquiry to convert a representative domain name to an IP address is received from the client-side DNS server
3
, the server-side DNS server
5
responds to the client-side DNS server
3
by converting the representative domain name to the IP address of either one of the servers
6
and
7
. That is, the server-side DNS server
5
sorts the access request from the client
2
by allocating it to either one of the servers
6
and
7
. This sorting constitutes the load balancing mentioned above.
In the above-described constitution, when accessing the virtual server of the representative domain name, for example in a step SA
1
the client
2
sends notification via the LAN/WAN
1
to the client-side DNS server
3
of the representative domain name corresponding to the IP address for which an inquiry has been received from the client-side DNS server
3
.
The client-side DNS server
3
determines whether the same inquiry has previously been received by accessing its own cash memory (not shown in
FIG. 18
) and consulting inquiry history data. When the same inquiry has previously been received, in a step SA
4
the client-side DNS server
3
notifies the client
2
via the LAN/WAN
1
of the IP address contained in the inquiry history data. The inquiry history data is held in the cash memory for approximately one day.
On the other hand, when the same inquiry has not previously been received, in a step SA
2
the client-side DNS server
3
sends an inquiry for DNS to the server-side DNS server
5
via the LAN/WAN
1
and the LAN/WAN
4
. Specifically, the client-side DNS server
3
notifies the server-side DNS server
5
of the representative domain name. Consequently, in a step SA
3
the server-side DNS server
5
consults a sorting table (not shown in the diagram) in which the server
6
is deemed a first server and the server
7
is deemed a second server, and converts the representative domain name for which notification has been received to, for example, the IP address of the first server
6
Mochizuki Tomotsugu
Ochi Akiyoshi
Okano Tetsuya
Takaba Koichi
Barot Bharat
Fujitsu Limited
Staas & Halsey , LLP
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