You know what a cloud is; you know there are three kinds of clouds, Infrastructure as a Service (IaaS); Platform as a Service (PaaS); and Software as a Service (SaaS); so what the heck is this public, private and hybrid cloud stuff?
It's actually pretty simple. No matter what kind of cloud you have, the servers it runs on have to live somewhere. A public cloud runs on servers at a third party's data-center. A private one runs on your servers at your data center. And, a hybrid runs its services on on both public and private clouds.
In use, you can mix and match these models. For instance, you might run your public Web servers on a public cloud; your corporate databases on a private one; and the front end to a SaaS from a public cloud while doing the authentication from your private-cloud back-end servers. In this case, you're not just using a hybrid cloud, you're actually using all three models.
So which kind of cloud is right for you? Well, it depends on what you want it to do. If on the top of your cloud to-do list you have these needs:
- Add computing resources dynamically
- Run standardized applications for multiple users
- Provide developers or DevOps staff with a testbed
You want a public cloud.
But if the factors below are vital to you:
- You need absolute control of your data and/or applications
- You must adhere strictly to data control regulations and laws, e.g. Health Insurance Portability and Accountability Act (HIPAA)
- You can afford to run a data center
then a private cloud may be your best choice.
If, like many businesses, you have a mixture of IT requirements, than a hybrid model would probably be your best choice.
Structurally this looks like it's easy to figure out. In practice it's more complicated.
As Forrester's cloud principal analyst James Staten recently blogged, if you're running any kind of SaaS application, you're already running a hybrid cloud.
"Hybrid isn't a future state after you have a private cloud in place and IT Ops chooses to connect that private cloud to a public cloud. Look at it through the lens of a business process or application service which is composed of different components, some cloud-based, some on-premise. From an Infrastructure & Operations perspective, hybrid cloud means a cloud service connected to any other corporate resource (a back office app, your web site, your intranet, another SaaS app you have under contract and yes, even your private cloud). Any of these types of connections presents the same integration impact - whether you established the connection or not."
What all this means is that while it's easy to define public, private, and hybrid cloud, putting together the right mix isn't easy. You need to carefully consider all your IT requirements and exactly how they'll work out with cloud technologies before moving from your 20th century server room and data center to your own special blend of cloud services.