An Inconvenient Truth of the NIST Definition of Cloud Computing
The classification and some definitions of the four deployment models are redundant and inconsistent
By: Yung Chou
Jan. 24, 2012 07:15 AM
Amid the many benefits of having the NIST SP 800-145 as a tool to facilitate the understanding of cloud computing, the classification and some definitions of the four deployment models are redundant and inconsistent. Particularly, the definition of "community cloud" is a redundancy of that of a private cloud, the deployment models are defined with two sets of criteria, and "hybrid cloud" is a confusing, ambiguous, and extraneous term.
SP 800-145 is the de facto standard in the IT industry of describing what cloud computing is with five essential characteristics, three delivery methods, and four deployment models. The five essential characteristics will specify the qualifications and expected behaviors of an object qualified with the term cloud. The three delivery methods signify the essence of cloud computing centered on the concept of a "service." Both the characteristics and the delivery methods in SP 800-145 form a solid foundation and present a conceptual model envisioning what cloud computing is and about. SP 800-145 gets inconvenient where the four deployment models including public, community, private, and hybrid clouds are defined, as shown below.
It is important to recognize that building a cloud with owned hardware does not default it as a private cloud of the owner's, while a cloud with accessibility via the Internet or operated by an internet service provider does not automatically make it a public cloud either. Again, the intended audiences determine it is a private or public cloud. Although many seem to default a private cloud as an on-premise deployment to owned hardware, this is nonetheless not a requirement of a private cloud.
Further "public" here does not suggest that it is free or accessible anonymously. It simply means the cloud is dedicated for the general public to consume, while there can be business or administrative restrictions imposed. Microsoft Office 365, available based on a subscription, and Hotmail, requiring a Live ID to sign, are vivid examples of public cloud offerings with restrictions.
Inconvenience #1: The classification of "community cloud" is extraneous.
Inconvenience #2: Using two sets of criteria to define cloud deployment models roots inconsistency and ambiguity.
Inconvenience #3: "Hybrid cloud" is an ambiguous, confusing, and frequently misused term.
For many enterprise IT professionals, a hybrid cloud means an on-premise private cloud connected with some off-premise resources. Notice these off-premise resources are not necessarily in reality a cloud. In such cases, it is simply a private cloud with some extended boundaries. A cloud is a set of capabilities and must be referenced in the context of the delivered application. Just placing a VM in the cloud or referencing a database placed in the cloud does not make the VM or the database a public cloud application.
The key is that a hybrid cloud is a derived concept of clouds. Namely, a hybrid can be integrations, modifications, extensions, or a combination of all of the cloud infrastructures. A hybrid is nevertheless not a new concept or a different deployment model and should not be classified as a unique deployment model in addition to the two essential ones, i.e., the public and private cloud models. A cloud is either public or private and there isn't a third kind of cloud deployment model based on the intended users.
"Hybrid cloud" is perhaps a great catchy marketing term. For many, a hybrid seems to suggest it is advanced, leading edge, and magical, and therefore better and preferred. The truth is "hybrid cloud" is an ambiguous, confusing, and frequently misused term. It confuses people, interjects noises into a conversation, and only to further confirm the state of confusion and inability to clearly understand what cloud computing is.
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