A public cloud is one in which "(t)he cloud infrastructure is made available to the general public . . . and is owned by an organization selling cloud services." (NIST) The cost of the infrastructure is shared across many organizations, and public clouds tend to be very large and thus able to take advantage of economies of scale. This means that applications can often be deployed in public clouds at lower costs than other cloud deployment models. On the other hand, data control represents a significant challenge for public cloud applications. Many companies house applications and confidential, proprietary data that would not be appropriate to be placed in a shared computing and storage environment.
A private cloud is one in which the ". . . infrastructure is operated solely for an organization." (NIST) Private clouds attempt to provide similar convenience and elasticity of resources that public clouds provide, but allow an organization much greater control over the location of and access to the company's applications and data.
A hybrid cloud deployment typically tries to maximize the benefits of both public and private clouds. A company will have two or more unique clouds available, but these clouds ". . . are bound together by . . . technology that enables data and application portability (e.g., cloud bursting for load balancing between clouds)." (NIST) Hybrid cloud deployments allow an organization to take advantage of the cost benefits associated with public clouds while simultaneously protecting confidential data in private clouds. Hybrid clouds also provide a mechanism for better business continuity and faster disaster recovery. If a public cloud hosting an application goes down, that application can theoretically be reinstantiated in the private cloud with little downtime.
Now that we've covered a lot of the generic cloud-related terminology and concepts, in the next post we'll begin an exploration into Eucalyptus, the company and the product.