Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing
Reexamination Certificate
2001-02-06
2004-04-06
Coulter, Kenneth R. (Department: 2141)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Least weight routing
C709S241000, C709S238000
Reexamination Certificate
active
06718359
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to computer networks in general, and in particular to load balancing client requests among redundant network servers in different geographical locations.
BACKGROUND OF THE INVENTION
In computer networks, such as the Internet, preventing a server from becoming overloaded with requests from clients may be accomplished by providing several servers having redundant capabilities and managing the distribution of client requests among the servers through a process known as “load balancing.”
In one early implementation of load balancing, a Domain Naming System (DNS) server connected to the Internet is configured to maintain several IP addresses for a single domain name, with each address corresponding to one of several servers having redundant capabilities. The DNS server receives a request for address translation and responds by returning the list of server addresses from which the client chooses one address at random to connect to. Alternatively, the DNS server returns a single address chosen either at random or in a round-robin fashion, or actively monitors each of the servers and returns a single address based on server load and availability.
More recently, a device known as a “load balancer,” such as the Web Server Director, commercially available from the Applicant/assignee, has been used to balance server loads as follows. The load balancer is provided as a gateway to several redundant servers typically situated in a single geographical location and referred to as a “server farm” or “server cluster.” DNS servers store the IP address of the load balancer rather than the addresses of the servers to which the load balancer is connected. The load balancer's address is referred to as a “virtual IP address” in that it masks the addresses of the servers to which it is connected. Client requests are addressed to the virtual IP address of the load balancer which then sends the request to a server based on server load and availability or using other known techniques.
Just as redundant servers in combination with a load balancer may be used to prevent server overload, redundant server farms may be used to reroute client requests received at a first load balancer/server farm to a second load balancer/server farm where none of the servers in the first server farm are available to tend to the request. One rerouting method currently being used involves sending an HTTP redirect message from the first load balancer/server farm to the client instructing the client to reroute the request to the second load balancer/server farm indicated in the redirect message. This method of load balancing is disadvantageous in that it can only be employed in response to HTTP requests, and not for other types of requests such as FTP requests. Another rerouting method involves configuring the first load balancer to act as a DNS server. Upon receiving a DNS request, the first load balancer simply returns the virtual IP address of the second load balancer. This method of load balancing is disadvantageous in that it can only be employed in response to DNS requests where there is no guarantee that the request will come to the first load balancer since the request does not come directly from the client, and where subsequent requests to intermediate DNS servers may result in a previously cached response being returned with a virtual IP address of a load balancer that is no longer available.
Where redundant server farms are situated in more than one geographical location, the geographical location of a client may be considered when determining the load balancer to which the client's requests should be routed, in addition to employing conventional load balancing techniques. However, routing client requests to the geographically nearest server, load balancer, or server farm might not necessarily provide the client with the best service if, for example, routing the request to a geographically more distant location would otherwise result in reduced latency, fewer hops, or provide more processing capacity at the server.
SUMMARY OF THE INVENTION
The present invention seeks to provide novel apparatus and methods for load balancing client requests among redundant network servers and server farms in different geographical locations which overcome the known disadvantages of the prior art as discussed above.
There is thus provided in accordance with a preferred embodiment of the present invention a method for load balancing requests on a network, the method including receiving a request from a requestor having a requestor network address at a first load balancer having a first load balancer network address, the request having a source address indicating the requestor network address and a destination address indicating the first load balancer network address, forwarding the request from the first load balancer to a second load balancer at a triangulation network address, the request source address indicating the requestor network address and the destination address indicating the triangulation network address, the triangulation network address being associated with the first load balancer network address, and sending a response from the second load balancer to the requestor at the requestor network address, the response having a source address indicating the first load balancer network address associated with the triangulation network address and a destination address indicating the first requestor network address.
Further in accordance with a preferred embodiment of the present invention the method includes maintaining the association between the triangulation network address and the first load balancer network address at either of the load balancers.
Still further in accordance with a preferred embodiment of the present invention the method includes maintaining the association between the triangulation network address and the first load balancer network address at the second load balancer, and communicating the association to the first load balancer.
Additionally in accordance with a preferred embodiment of the present invention the method includes directing the request from the second load balancer to a server in communication with the second load balancer, composing the response at the server, and providing the response to the second load balancer.
There is also provided in accordance with a preferred embodiment of the present invention a method for load balancing requests on a network, the method including determining the network proximity of a requestor with respect to each of at least two load balancers, designating a closest one of the load balancers by ranking the load balancers by network proximity, and directing requests from the requestor to the closest load balancer.
Further in accordance with a preferred embodiment of the present invention the method includes directing requests from any source having a subnet that is the same as the subnet of the requestor to the closest load balancer.
Still further in accordance with a preferred embodiment of the present invention the method includes monitoring the current load of each of the load balancers, and performing the directing step the current load of the closest load balancer is less than the current load of every other of the load balancers.
Additionally in accordance with a preferred embodiment of the present invention the determining step includes periodically determining.
Moreover in accordance with a preferred embodiment of the present invention the determining step includes determining at at least one fixed time.
Further in accordance with a preferred embodiment of the present invention the determining step includes polling the requestor to yield at least two attributes selected from the group consisting of: latency, relative TTL, and number of hops to requestor.
Still further in accordance with a preferred embodiment of the present invention the determining step includes polling the requestor using at least two polling methods selected from the group consisting of: pinging, sending a TCP ACK message to
Peless Amir
Zisapel Roy
Coulter Kenneth R.
Radware Ltd.
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