First, we should clear up the confusion about what is a cloud? Cloud is a commonly misused term used to describe just about any service accessed over the internet. That’s typically also described as public cloud, because it’s accessible by the public. These two words, public cloud, are incorrect for two reason. First, just because it’s available over the internet doesn’t make it a cloud. Secondly, just because the public has access to an internet service doesn’t mean it’s a public cloud.
What is cloud?
Yung Chou at Microsoft nicely summarized the principles of cloud computing. In short, a cloud is a pooled set of elastic resources. In the traditional data center, you’re generally not using its resources to its fullest capacity. This leaves a lot of resources sitting idle. Cloud infrastructure is far better at resource management. Resources are pooled into one big group for applications to use as needed. The virtual nature of these resources, and pooling, makes clouds far more efficient. Resource pooling allows cloud services to easily move across physical devices.
A cloud can readily provision resources on demand because they are virtual. This includes storage, computing and even network resources. You can easily expand a cloud’s performance and capacity by adding more hardware. For example, a storage volume can increase its performance by adding more physical drives, allowing more parallelism. Attach flash devices for caching. Add drives for edge caching at different geographies or for redundancy, making the virtual storage more resilient.
What is a public cloud?
Assuming what we’re talking about hereafter is a true cloud infrastructure, why is it called public cloud? Different people or organizations, called tenants, share a public cloud. Because the resources are virtual, different tenants will be using the same physical resources. Public cloud is simply a cloud infrastructure shared by multiple tenants.
In a public cloud your services are running on a physical server also used by others. You are paying a service provider to manage those physical resources for you. It’s more like renting an apartment, than owning a house. It comes with advantages and disadvantages. If there’s a problem with the plumbing, you call the landlord. But what if you want to remodel the kitchen? You’re not allowed to do that.
What is a private cloud?
Based on the term public is the alternative private cloud. The term private is the opposite of public so we can assume that’s why it’s used. Unfortunately, private implies privacy, but that’s not what a private cloud is describing at least not entirely. It’s private because you’re not sharing the resource with others. A private cloud is when you own and manage the physical resources. You may even share them with other tenants, but it’s still private because it’s privately owned.
Think of it this way. Your city might have a pool available to the community. That’s a public pool. The community is sharing it, and it’s maintained by the city. Some people want a pool, but putting a pool in their backyard isn’t an option. They use the public pool instead. For this convenience, they make compromises to share the resource with other, which may include privacy but it could be for other reasons such as cost or skills.
You might have a pool in your backyard. That’s a private pool. You may not want a private pool only because of privacy. You may prefer to design and build one that better fits your needs. Maybe you’re into fitness and want to swim laps without the crowd. Maybe you want to avoid noisy children splashing and shouting “marco polo”.
Why would you need a private cloud?
You want to avoid the noisy neighbor problem common within a data center using shared resources, as this can rob you of those resources (even if it’s just temporary). Maybe you have a specific need that is best suited by your own design. You might have a security requirement, and cannot allow your data on shared resources or accessible to IT staff who are not your employees. Financial and medical industries are highly regulated, and there are laws that prevent them from putting certain data in a public cloud. For other organizations with big data it’s impractical to transfer terabytes of data. Big data would perform poorly if the traffic must transfer across different geographies.
Simply stated, private cloud is the physical cloud infrastructure you own and control. Others do not share your resources. You design infrastructure optimized to meet your specific needs. Big data performs better on your premises, within your local network, providing you higher bandwidth and lower latency. Your data is secure on servers you own, only available to your employees. You do with these resources as you wish.
What’s the difference between public and private cloud?
Technically there’s no difference between the two.
- The meaning of “public” in public cloud: Shared virtual resources you do not own and do not manage.
- The meaning of “private” in private cloud: Physical resources you own and manage.
What is hybrid cloud?
Just about all organizations have private resources. Many of those organization also pay for sharing pubic resources. The challenge of having both a private and public infrastructure, on different networks, is integrating them in a seamless way. This is the case for a hybrid cloud. It’s the integration of your (private) physical and the (public) virtual shared resources.
Now that you realize what is hybrid cloud, it should be clear for anyone considering a public cloud that hybrid is very likely what you need. Gartner has reported companies with successful hybrid clouds demonstrate four key competencies.
This option is commonly referred to as co-location. The hosting service provides the cabinets, cages, fire protection, cooling, and an isolated network. You might choose this because you don’t have an adequate data center or outsource some of the basic management tasks is more economical. The hosting service might also provide some IT services as well. This is a hybrid IT model where you have a private cloud hosted off premise by a service provider. Now don’t confuse this with a hybrid cloud. Did I just confuse you? Sorry! Just ignore that last point. I’ll cover hybrid IT in another article.