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Several collocation service providers, or Web-hosting companies that lease data-center space for hosting Web servers, are now embracing the concept of a CDN as a value-added service. This is a natural extension to their business model, since these companies already have data-center infrastructure and a customer base to which they can sell the service. The Web-hosting company deploys caches in its data centers and uses global server load balancing to direct the users to the closest cache. When a customer subscribes to the service, the customer can deploy Web servers in one data center and serve content from all data centers. The service provider simply configures the global load balancer to take over the DNS functions for the customer and provides appropriate DNS replies directing users to the closest set of caches. To scale the number of caches in each data center, we can use server load balancers in front of the reverse-proxy caches and distribute the load. The collocation and Web-hosting service providers find the CDN service to be a way to obtain general incremental revenue and profits, without a huge investment.
Chapter 9: The Future of Load-Balancing Technology
load balancing has evolved as a powerful way to solve many network and server bottlenecks. What started as simple server load balancing evolved to address traffic distribution to caches and firewalls and even across data centers. As load balancers continue to evolve, they are being deployed for new types of applications.
Load balancers are used by many as a security device because of their capabilities to provide stateful intelligence, access-control lists, and network-address translation. Many load balancers also provide protection against some forms of security attacks.
Over the next few years, load-balancing technology is likely to evolve in several dimensions. Load-balancing products exhibit the same characteristics as any new technologies: declining prices, increased functionality, improved performance, better port density and form factors, and so on. In this chapter, we look at the future of load balancing for different applications.
Server load balancing
So far, load balancers are predominantly used in the Web-related infrastructure, such as Web servers, FTP servers, streaming-media servers, and so forth. Any Web-based application is a good candidate for load balancing because it’s a nicely divisible problem for performing load distribution. But load balancers will probably evolve to encompass file servers, database servers, and other applications. While some of these can actually be done even today, there is no widespread adoption for load-balancing these applications yet. Many of these new applications will require close collaboration between the load-balancer vendors and the application vendors.
As the power and functionality of load balancers continues to increase, load balancers may evolve to become the front-end processors (FEP) for server farms. Load balancers may actually be able to implement a certain amount of server functionality to pre-process requests, thus reducing the amount of server processing capacity required. Load balancers may themselves act as a superfast, special-purpose appliance server. In the Internet age, many servers spend the majority of the time as packet processors, where the servers are simply processing IP packets that consume significant amounts of processor resources. Since the load-balancer products may not have the same overhead as a server with a general-purpose operating system, the load balancer is likely to provide superfast performance and ultra-low latency for certain special functions, such as value-added IP packet processing. It will be interesting to look out for a successful business model that can turn this into a reality.
The Load Balancer as a Security Device
While firewall load balancing can enhance the scalability and availability of firewalls, the load balancer itself can perform several security functions either to complement the firewalls or to offload the firewalls from certain performance-intensive tasks. For example, the load balancers can perform NAT and enforce access-control lists to reduce the amount of work and the traffic for the firewalls. Further, load balancers can use stateful intelligence to perform a certain amount of stateful inspection to protect against certain types of attacks from malicious users. Since the load balancer fits between the edge router and the firewalls, the load balancer may be able to offload the router from the burden of enforcing Access Control Lists (ACLs) and provide a better ACL performance than some legacy routers. On the other side, the load balancer can offload the NAT functionality from the firewalls and provide an extra layer of protection before the firewalls by stopping certain forms of Denial of Service (DoS) attacks.
Cache load balancing
It will be interesting to see whether the load-balancing products can extend to implement complete firewall functionality and gain widespread market acceptance.