The Internet is much larger than the World Wide Web. Although more and more services are being built on top of HTTP due to its prevalence, a plethora of commonly used protocols are available for external and internal services. The distinct advantage of load balancing devices that do not operate above layer 4 is that they are multidisciplinary. Load balancing devices that operate on layer 3 or layer 4 (like most web switches and IPVS solutions) are capable of distributing service load across real servers for almost any IP-based protocol. A few of the most commonly load balanced IP-based protocols are
Regardless of the need, almost every large architecture has at least one load balancer deployed to distribute some IP traffic. For architectures that are centralized (single geographic installation), the choice to use an expensive, high-performance load balancer is usually sound. As illustrated in Chapter 4, load balancing does not provide high availability. Because there is still a single point of failure when deploying load balancers, two must be deployed, and a high availability solution must be instantiated between them. The "expensive" load balancer just doubled in price.
For centralized architectures, two devices often suffice, which makes the costs understood and usually reasonable. However, when an architecture decentralizes for political, business, or technical reasons, scalability is no longer efficient. The expensive price for dual load balancers now must be replicated across each cluster. Given four installations throughout the world, eight load balancers must be purchased for high availability, load balancing, and consistency. At that point, alternative approaches may be more appropriate.