Before we look at clustering techniques, let's discuss the concepts and differences between scaling up and scaling out.
One way to deal with increased traffic is to scale a web service's underlying infrastructure vertically, or up. By leveraging the latest server architectures with powerful CPUs and sufficient memory, service designers can improve the throughput of their systems. However, this approach is bounded by the servers' physical limitations. Once these limitations are reached, throughput can no longer be improved. In addition, this approach may not make economic sense. Indeed, the cost of the latest generation of servers might prove to be prohibitive.
Tip
This technique is often used in data-tiers. Due to the deployment complexity of database sharding, it often makes more sense to scale up the persistence infrastructure. This allows you to delay the addition of this extra complexity until it is no longer avoidable.
By contrast, scaling horizontally...