If your IT environment is not running in the public cloud, then you are either using on-premises infrastructure or a private cloud. What’s the difference between the two, and why is it important?
There is little debate about the definition of the public cloud. The public cloud is the cloud of hyperscalers. AWS, Google, Microsoft, Oracle or other players offer you measured and flexible services on their infrastructure.
You can purchase scalable storage or compute power, choosing from pure infrastructure, or more managed solutions. The pinnacle of public cloud is serverless offerings, where workloads just always get exactly the computing power they need, courtesy of the cloud provider. The bill, of course, will follow at a later date.
Sharing with others
There is one constant: the cloud provider owns and manages the IT infrastructure. Workloads are distributed among the provider’s servers. Which provides efficient hardware, and sells virtualized computing power to customers. Your virtual machine with four computing cores and 8 GB of RAM might be running alongside a competitor’s on a single powerful machine with 128 cores and 256 GB of RAM.
The public cloud offers scalability, flexibility and relief, but it also has a downside. Maybe you want more control over your hardware, or maybe the subscription model for your stable workloads turns out to be more expensive than expected after all. Or maybe workloads need to run locally for performance or security reasons.
Leaving the public cloud aside, you have a choice between two options between which the distinction is not always clear: private cloud or on-premises. To put the two side by side, it is important to agree on the definition.
On-premises
On-premises, often abbreviated to on-prem, literally means “on premises,” referring to an enterprise’s own location. Sometimes organizations still incorrectly use the term “on-premises” without an “s,” but that’s wrong and doesn’t make sense in terms of content. On-premises infrastructure can be thought of as a counterpart to public cloud infrastructure.
On-prem hardware is generally located in the company’s own data center. That may be a large server room, a real proprietary data center or a broom closet. Proprietary space can also be rented, in a colocation data center, for example. The colocation specialist there handles the power and cooling of the hardware, but we still consider that on-premises.
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On-premises, public or private cloud: what’s the difference?
In any case, the organization has complete control over the hardware. Servers are ordered and assembled according to the company’s own requirements. It is up to the company’s IT team to ensure that sufficient storage and computing power is available for the organization’s needs.
On-prem infrastructure is often synonymous with a more classic IT environment, in which several servers support each person’s concrete workloads. However, more modern hardware implementations such as hyper-convergedinfrastructure (HCI) are also possible in an on-prem context, as long as the hardware is managed by the enterprise itself.
Private cloud
Private cloud, like on-premises, is a counterpart to public cloud, but the approach is different. With on-premises, the focus is on the infrastructure, its deployment and management. The term private cloud refers to the flexibility of the offering, which is similar to public cloud.
As in the public cloud, in the private cloud you can allocate virtual machines based on your needs, and you can assign workloads more or less horsepower. The main difference is that the underlying infrastructure is not shared with other customers but – as the name suggests – is private. No other customers in the data center can touch the storage, compute power or network infrastructure of a company’s private cloud.
There are several ways to build a private cloud. You can do it yourself, with your own hardware in your own data center or with a colocation specialist. In that case, the private cloud runs on-premises and the two come together.
You can also partner with a hardware manufacturer that offers a cloud-like subscription model for servers where you rent them based on usage, but do not share them with third parties. Lenovo TruScale, Dell Apex and HPE Greenlake are the best-known examples.
Finally, you can partner with a provider for a private cloud, analogous to a public cloud provider. The key difference remains that the entire physical IT infrastructure is exclusively at your disposal. Major cloud providers such as Azure, AWS and Google all offer private cloud offerings in addition to their public offerings. Functionality is similar, but access to the infrastructure remains private for the customer.
Who owns and what do you share?
As you read, on-premises and private cloud are not juxtaposed but overlapping. On-premises refers to the management and ownership of the infrastructure. You can run a private cloud on on-premises infrastructure, or choose an old-fashioned 3-tier approach with storage, network and compute power as separately purchased building blocks.
With on-premises infrastructure, you own your servers: you choose the hardware and you decide how modern or classic the infrastructure behind your IT environment is. The payment model is secondary. You can also rent servers if you want, as long as they are in a location of your choosing, and you have full access.
With on-premises infrastructure, you own your servers.
Private cloud is a model on top of IT infrastructure. Where the private cloud runs and who owns the hardware does not matter much. What does matter is that the private cloud runs on servers assigned exclusively to the customer, in a network set up exclusively for the customer. If you run one virtual machine with eight compute cores on a server with 64 compute cores, then the remaining 56 cores are at your disposal. You can deploy them whenever you want, and at no time are they assigned to another company’s VM.
Flexibility with a price tag
A private cloud works as flexibly as a public cloud. For example, you can allocate available compute power and storage for workloads through a cloud portal, without having to allocate an entire server to a task. You can also allocate more or less horsepower or storage to a workload to the extent necessary, just as with the public cloud.
The big difference: because the servers behind the private cloud are reserved exclusively for you, that computing power has to be ready. Do you suddenly need 24 extra cores and 64 GB of RAM? Then it has to be ready. In other words, you have to have purchased them (on-premises) or requested them from your private cloud provider. That takes longer than in the public cloud, where the public cloud provider always provides available computing power.
Because you have to provide that growth space yourself, you have to overprovision a bit. In this way, you pay not only for what you consume, but for a chunk of the hardware you keep in reserve for your growing consumption.
If you choose your own hardware, either through a private cloud arrangement or because you keep everything on-premises, then you have to take that into account. Scaling up is possible, but not à la minute like in the public cloud. In a purely on-premises context, everything depends on delivery time. If you work with a private cloud partner without purely on-premises infrastructure, then scaling up can be faster.
When and why?
So when do you choose the public cloud, when a private cloud, and when do you additionally consider on-premises infrastructure?
Public cloud
- A model for IT consumption
- Complete hardware relief
- You configure what you need
- You securely share the environment with other clients
- Always through an external data center
Private cloud
- A model for IT consumption
- Functions a lot like the public cloud
- The underlying hardware is private
- Workloads also scale flexibly, as long as the necessary hardware is available
- You can provide hardware yourself (on-premises) or partner with a partner
- Can be local (low latency) or in a remote data center
On-premises
- A model for IT hardware management
- You place your own hardware in a location of your choosing
- You are responsible for the availability of IT capacity
- You can totally choose how to deploy on-premises hardware (3-tier, HCI, private cloud…)
- Usually in an in-house data center (low latency), but colocation is also possible
Thus, public cloud remains a smart choice for unpredictable workloads that need to scale quickly. Private cloud is a model that attempts to emulate the convenience of the public cloud, but within a private context. Because hardware is not shared, this model theoretically offers more privacy and security. That can be important for parties in the financial or health care sectors that need to adhere to strict regulations.
If you choose private cloud with a third-party provider, the difference with public cloud is actually not that big anymore. Virtualized workloads are separated in the public cloud in such a way that the security risk is theoretical for most types of customers.
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On-premises, public or private cloud: what’s the difference?
On-premises implies in-house management of the hardware. There the benefits are greater, though. If you know how much IT capacity you will need over the next few years, you can buy it reasonably measured. That will often turn out to be more economical than running a stable workload with a public cloud provider anyway.
On-premises infrastructure offers another advantage of lower latency, especially when the data center is really close to the organization. For example, an animation studio wants instant access to immense files without sending them back and forth over the public Internet.
A little bit of everything: hybrid cloud
So what is the best choice? That depends from company to company, and in fact even from workload to workload. Cloud first is a marketing cry that we are thankfully hearing less and less in the meantime. Some workloads benefit from scalability, others from flexibility but must run in accordance with complex regulations, and still others are stable and simply best available as close to the end user as possible.
The perfect solution is often an amalgamation of one or more public and or private cloud providers and on-premises infrastructure: the hybrid cloud.