What Is Best Suited For The Cloud? - Page 2
Scale-out Load Balanced Apps with Disposable Instances
This type of application does not rely on any one instance of software being able to grow to use tremendous amounts of compute resource. Rather it assumes that each instance can only do so much and that additional power will be supplied by adding more instances. For this sort of application to work the data and other application state must be driven out of the application itself to another location.This allows instances to be created and destroyed with no data loss or outage to the end user. The worst problem caused by failure of an instance is the need for the end user to retry their operation. When the operation is retried, it finds a live instance and completes without difficulty.
Generally, the application requires greater or lesser instances over time as load grows and shrinks. This creates a need for dynamism in the deployment with low turn-around time on provisioning operations. As load grows, the application must respond in a short period of time. Either the application administrator or some auto-scaling management system needs to be able to make the required changes without a ticket to the infrastructure team. When load is high, new instances must be spawned to handle the increased demands. When load drops, instances should be deleted to reclaim compute resources for more useful activity. Because the instances are stateless, without sufficient load that needs to be serviced, no instance has an inherent reason to remain persistently deployed.
Scale-out applications are also a great fit with the datacenter operations models required to manage a massive cloud. Cloud scale datacenters need to assume that any piece of equipment can break at any time with the application being resilient and able to hide the failure from the end user. Scale-out applications accomplish this by spreading many instances across nodes, datacenters, or even geographies. This makes it much simpler for the infrastructure to be managed – failures become a capacity issue which can be managed in aggregate on a periodic basis, not end-user outage issues that need to be addressed immediately and individually.
More generally, this type of application is the way of the future in general. Due to current systems architectures, we are seeing more and more cheaper cores distributed across many commodity nodes rather than the massive scaling up of individual servers. The only way to really get applications to scale is to build for many smaller instances teaming up together. Some programming infrastructures take this to a logical conclusion. Node.js, a language increasingly used for scale-out web applications, refuses to give a program access to more than one core regardless of how many cores are in a system. Should the developer need more power, they need to increase the number of node.js application instances.
Scale-out applications and cloud are such a good match because they have the same goals – elastically, scale up and down in response to load using only the resources actually needed, distributing applications across hosts and sites to better tolerate systems outages without end user impact and better conformation to modern system architecture.