Affinity-based router and routing method

Details Affinity-based router and routing method Affinity-based router and routing method

1997-10-08

2002-07-23

Sheikh, Ayaz (Department: 2155)

Electrical computers and digital processing systems: multicomput

Distributed data processing

Client/server

C709S226000, C370S237000

Reexamination Certificate

active

06424992

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to providing load balancing across distributed computing systems. More particularly it relates to a routing method for use in distributed systems including a set of server computing nodes, all or a subset of which can handle a client request, but where there is a preferred node or a set of nodes that are best suited to handle a particular client request.
GLOSSARY OF TERMS
While dictionary definitions apply to the terms herein, the following definitions of some terms are also provided to assist the reader:
An Encapsulated Cluster (EC) is characterized by a Connection-Router (CR) node and multiple server hosts providing a set of services (e.g. Web service, NFS, etc.). An example of a system which provides encapsulated clustering is described in U.S. Pat. No. 5,371,852, entitled “METHOD AND APPARATUS FOR MAKING A CLUSTER OF COMPUTERS APPEAR AS A SINGLE HOST ON A COMPUTER NETWORK”.
A virtual encapsulated cluster system describes an improvement to the aforementioned U.S. Pat. No. 5,371,852. Like the system of U.S. Pat. No. 5,371,852, a Virtual Encapsulated Cluster routes TCP information that crosses the boundary of a computer cluster. The information is in the form of port type messages. Incoming messages are routed and the servers respond so that each cluster appears as a single computer image to the external host. In a virtual encapsulated cluster a cluster of servers with a single TCP-router node is divided into a number of virtual clusters. Each virtual encapsulated cluster appears as a single host to hosts on the network which are outside the cluster. The messages are routed to members of each virtual encapsulated cluster in a way that keeps the load balanced among the set of cluster nodes.
A recoverable virtual encapsulated cluster is a virtual encapsulated cluster which has two TCP-router nodes, a primary and a backup. The cluster is augmented with a recovery manager which causes the backup TCP-router to become active if the primary fails. In addition methods are added so that the connection state at the time of failure can be reconstructed by (or alternatively known at) the backup router so that zero or the minimum number of client connections will be lost due to failure of the TCP-router node. Methods are also added so that the configuration/management information of the virtual encapsulated cluster are replicated (or constructed) at the backup. Finally the start up protocol of the TCP-router node is changed so that recovery of the primary router will not cause a failure in a backup which has taken over for it. This is described in the aforementioned co-pending patent application entitled “Weighted TCP Routing to Service Nodes in a Virtual Encapsulated Cluster,” by Attanasio et al.
BACKGROUND
The traffic on the World Wide Web is increasing exponentially, especially at popular (hot) sites. In order to increase the processing capacity at such hot sites, a cluster of computing nodes, which we will refer to as a multi-node cluster, can be provided to handle the load. The multi-node cluster is (encapsulated) made to appear as one entity to clients, so that the added capacity provided by the multi-node cluster is transparent to clients. Client requests need to be distributed among nodes in the multi-node cluster.
One known method in the art that attempts to balance the load among nodes in a multi-node cluster is known as the Round-Robin Domain Name Server (RR-DNS) approach. The basic domain name server method is described in the paper by Mockapetris, P., entitled “Domain Names—Implementation and Specification”, RFC 1035, USC Information Sciences Institute, November 1987. In the paper by Katz., E., Butler, M., and McGrath, R., entitled “A Scalable HTTP Server: The NCSA Prototype”, Computer Networks and ISDN Systems, Vol. 27, 1994, pp. 155-164, round-robin DNS (RR-DNS) is used to balance the load across a set of web server nodes. In this approach, the set of nodes in the multi node server is represented by one URL (e.g. www.hotsite.com); a cluster subdomain for this distributed site is defined with its subdomain name server. This subdomain name server maps client name resolution requests to different IP addresses in the distributed cluster. In this way, subsets of the clients will be pointed to each of the geographically distributed sites. Load balancing support using DNS is also described in the paper by Brisco, T., “DNS Support for Load Balancing”, RFC 1794, Rutgers University, April 1995.
A key problem with this approach is that the RR-DNS leads to poor load balance among the distributed sites, as described in the paper, Dias, D. M., Kish, W., Mukherjee, R., and Tewari, R., “A Scalable and Highly Available Web Server”, Proc. 41st IEEE Computer Society Intl. Conf. (COMPCON) 1996, Technologies for the Information Superhighway, pp. 85-92, Febuary 1996. The problem is due to caching of the association between names and IP addresses at various name servers in the network. Thus, for example, for a period of time (time-to-live) all new clients behind an intermediate name server in the network will be pointed to just one of the sites. This leads to hot spots on nodes of the server cluster that move to different cluster nodes as the time-to-live periods expire.
One known method to solve this problem within a cluster of nodes at a single site is to provide a encapsulated cluster using a so-called TCP router as described in: Attanasio, Clement R. and Smith, Stephen E., “A Virtual Multi-Processor Implemented by an Encapsulated Cluster of Loosely Coupled Computers”, IBM Research Report RC 18442, 1992, and, U.S. Pat. No. 5,371,852, Dec. 6, 1994, by Attanasio et al., entitled “Method and Apparatus for Making a Cluster of Computers Appear as a Single Host” (Attanasio). Here, only the address of the TCP router is given out to clients; the TCP router distributes incoming requests among the nodes in the cluster, either in a round-robin manner, or based on the load on the nodes. In Attanasio, the TCP router can act as a proxy, where the requests are sent to a selected node, and the responses go back to the TCP router and then to the client. This proxy mode of operation can lead to the router becoming a bottleneck, and for this reason is not considered further herein. In another mode of operation, which we will refer to as the forwarding mode, client requests are sent to a selected node, and the responses are sent back to the client directly from the selected node, bypassing the router. In many environments, such as the World Wide Web (WWW) the response packets are typically much larger than the incoming packets from the client; bypassing the router on this response path is thus critical.
The work described in the previous paragraph was expanded upon and improved in the co-pending patent application Ser. No. 08/701,939 “Weighted TCP Routing to Service Nodes in a Virtual Encapsulated Cluster” by C. Attanasio, G. Hunt, G. Goldszmidt, and S. Smith. This patent application describes how the same facility can be made recoverable. The TCP router is enhanced to handle virtual clusters, and multiple target addresses within a router, and the manager component is described which collects information and dynamically controls the weighted routing.
As described above, the TCP router would typically send different client TCP connection requests to different nodes within a cluster. There are several applications where specific multi-node servers would be preferred for certain client requests, based on either the static or dynamic state of system. Thus a key problem with the TCP router approach is providing support for client requests with affinity requirements.
An important example of this is the support of the Secure Sockets Layer (SSL) protocol, which is a very popular protocol used for the exchange of secure information between clients and servers on the WWW, and for other environments. In SSL, a session key is generated by the client, and passed to the server after encrypting it using the server's public key. Session keys have a lifetime (e.g. 100

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