What does the word “gift” mean to you? In English, it most often refers to a present or something given voluntarily. In German, it has a completely different meaning: “poison.” If a box marked “gift” is placed in front of an English-speaker, it’s safe to assume that he or she would interact with it very differently than a German-speaker would.
In the same way, simple words like “public,” “private,” and “hybrid” in cloud computing can mean very different things to different audiences. But unlike our “gift” example above (which would normally have some language or cultural context), it’s much more difficult for cloud computing audiences to decipher meaning when terms like “public cloud,” “private cloud,” and “hybrid cloud” are used.
We, as an industry, need to focus on semantics.
In this two-part series, we’ll look at three different definitions of “public” and “private” to set the stage for a broader discussion about “hybrid.”
“Public” v. “Private”
Definition 1—Location: On-premises v. Off-premises
For some audiences (and the enterprise market), whether an infrastructure is public or private is largely a question of location. Does a business own and maintain the data centers, servers, and networking gear it uses for its IT needs, or does the business use gear that’s owned and maintained by another party?
This definition of “public v. private” makes sense for an audience that happens to own and operate its own data centers. If a business has exclusive physical access to and ownership of its gear, the business considers that gear “private.” If another provider handles the physical access and ownership of the gear, the business considers that gear “public.”
We can extend this definition a step further to understand what this audience would consider to be a “private cloud.” Using this definition of “private,” a private cloud is an environment with an abstracted “cloud” management layer (a la OpenStack or CloudStack or VMWare) that runs in a company’s own data center. In contrast, this audience would consider a “public cloud” to be a similar environment that’s owned and maintained by another provider.
Enterprises are often more likely to use this definition because they’re often the only ones that can afford to build and run their own data centers. They use “public” and “private” to distinguish between their own facilities or outside facilities. This definition does not make sense for businesses that don’t have their own data center facilities.
Definition 2—Population: Single-tenant v. Multi-tenant
Businesses that don’t own their own data center facilities would not use Definition 1 to distinguish “public” and “private” infrastructure. If the infrastructure they use is wholly owned and physically maintained by another provider, these businesses are most interested in whether hardware resources are shared with any other customers: Do any other customers have data on or access to a given server’s hardware? If so, the infrastructure is public. If not, the infrastructure is private.
Using this definition, public and private infrastructure could be served from the same third-party-owned data center, and the infrastructure could even be in the same server rack. “Public” infrastructure just happens to provide multiple users with resources and access to a single hardware node. Note: Even though the hardware node is shared, each user can only access his or her own data and allotted resources.
On the flip side, if a user has exclusive access to a hardware node, a business using Definition 2 would consider the node to be private.
Using this definition of “public” and “private,” multiple users share resources at the server level in a “public cloud” environment—and only one user has access to resources at the server level in a “private cloud” environment. Depending on the environment configuration, a “private cloud” user may or may not have full control over the individual servers he or she is using.
This definition echoes back to Definition 1, but it is more granular. Businesses using Definition 2 believe that infrastructure is public or private based on single-tenancy or multi-tenancy at the hardware level, whereas businesses using Definition 1 consider infrastructure to be public or private based on whether the data center itself is single-tenant or multi-tenant.
Have we blown your minds yet? Stay tuned for Part II, where we’ll tackle bare metal servers, virtual servers, and control. We’ll also show you how clear hybrid environments really are, and we’ll figure out where the heck we go from here now that we’ve figured it all out.