1.4 Using Appliances
Today the most common implementation of services is through appliances, typically deployed centrally. These network devices implement services such as firewall, load balancing, and VPN termination. These are discrete boxes, and the traffic is sent to them explicitly in a technique called tromboning (see section 2.7). These devices become natural bottlenecks for traffic and impose a weird routing/forwarding topology. They are very high-cost, high-performance devices, and even the most capable ones have limitations in performance when compared to the amount of traffic that even a small private cloud can generate. These limitations, plus the fact that a packet must traverse the network multiple times to go through service chaining, result in reduced throughput and high latency and high jitter.
A distributed services platform avoids these large centralized appliances and relies on small high-performance distributed services nodes (DSNs) located as closely as possible to the final applications they serve. They are also multifunctional; that is, they implement multiple services and can chain them internally, in any order, without needing to traverse the network numerous times.