Server load balancing architectures, Part 2: Application-level load balancing

The transport-level server load balancing architectures described in the first half of this article are more than adequate for many Web sites, but more complex and dynamic sites can't depend on them. Applications that rely on cache or session data must be able to handle a sequence of requests from the same client accurately and efficiently, without failing. In this follow up to his introduction to server load balancing, Gregor Roth discusses various application-level load balancing architectures, helping you decide which one will best meet the business requirements of your Web site.

The first half of this article describes transport-level server load balancing solutions, such as TCP/IP-based load balancers, and analyzes their benefits and disadvantages. Load balancing on the TCP/IP level spreads incoming TCP connections over the real servers in a server farm. It is sufficient in most cases, especially for static Web sites. However, support for dynamic Web sites often requires higher-level load balancing techniques. For instance, if the server-side application must deal with caching or application session data, effective support for client affinity becomes an important consideration.

Here in Part 2, I'll discuss techniques for implementing server load balancing at the application level to address the needs of many dynamic Web sites.

Read the rest of the article on JavaWorld.