Best effort versus reliable clouds

Not every IaaS cloud service is the same. There are some fundamental differences between IaaS clouds. The main difference is in the architecture of the platform. Gartner has named the two most common architectures a best effort cloud and a reliable cloud. Other names for these different types of clouds are designed for failure versus enterprise clouds or stateless cloud service model versus stateful cloud service model.

A designed for failure cloud has been designed for running applications that have resiliency built into the application. This means that when a particular part of the application fails, the application continues to be available. This comes down to an application made up of many different virtual machines. Think about an application with a web tier, an application server tier, and a database tier. Each tier has at least two nodes so that if one node fails, the application will continue to be available.

A best effort cloud uses commodity hardware with no redundancy built into the hardware. For example, there is only one power supply, and a single fan for cooling. There is a single top-of-rack switch, no live migration of virtual machines, and so on. In some cases, the cloud provider does not have a Service Level Agreement available for single instance virtual machines.

As virtual machines are nonpersistent, there is no need for backup virtual machines. Backup at the storage layer is good enough.

Microsoft Azure is an example of a best effort cloud. In the next section, you will learn why.

A reliable cloud has been designed to host legacy, non-cloud ready applications that have single points of failures built into the application. In this cloud, the infrastructure is designed such that it provides resiliency for the application. An enterprise class with redundant components is the server hardware used. The cloud platform provides high availability and fault tolerance.

Virtual machines are persistent and a frequent backup is required. VMware vCloud Air and other VMware vClouds are examples of reliable cloud platforms.