Servicing a Web Site with Active Server Pages

Web sites that use Active Server Pages (ASP) can maintain session state across client connections. Network Load Balancing helps preserve client access to session information by ensuring that all TCP/IP connections from a single client are directed to the same cluster host. To do so, set Affinity to either Single or Class C.

There are, however, situations in which a client can connect with one cluster host, and then have subsequent connections load-balanced to different hosts. Such situations include the following:

• A host is added to the cluster, and Network Load Balancing load-balances new connections from this client to the host.
  Note that existing connections are unaffected.

• Multiple client-side proxy servers cause multiple connections from the same client to originate from different IP addresses.

If either of the preceding situations arises, ASP applications must provide a means to retrieve and manage session state even if a client connects to multiple cluster hosts as part of a single session. The following are two strategies for addressing this issue:

• Use a means at the ASP level, such as a cookie, to retrieve the ASP client state across the Network Load Balancing cluster nodes.

• Encapsulate in a client-side cookie the state from a specific client request. The cookie gives the server the context for subsequent client requests. This solution works only if there is a relatively small amount of state associated with each client transaction. As state grows larger, it becomes increasingly difficult to have the client forward a large cookie to the server with every request.

For more information about port-rule settings, see "IIS Server (Web Farm)," earlier in this chapter.