How to choose the right cloud service model for your organisation

There aren't many other technological shifts that have generated quite as much jargon as cloud computing. Now that around 78% of organisations have formally adopted at least one cloud-based service, it's important to cut through the noise of cloud buzzwords and understand what cloud services can really do for us. So what are the different types of cloud service models, and which one should you be using?

It is worth noting that one of the reasons for the differences in use of some of these terms is to better serve the vendors who provide them.

Smaller service providers often use "public cloud" as a term of derision. They say that they provide secure private clouds – not like the big global "public" clouds.

The larger providers tend to do the opposite. AWS notably (the largest cloud provider) don't use the term "public cloud". For them, there is "Cloud computing" which is what they do, and then everything else.

NIST (National Institute of Standards and Technology) offer the most widely accepted definitions of the different service models and, as a rule, these are the ones we use when describing cloud services. At a recent event we heard a telecoms provider use the distinction of how you connect to the cloud to be the defining characteristic. In short, if you connect over the internet – it's a public cloud, if you connect directly though a leased line rather than a VPN - you have a private cloud. Here's our take on it.

Multi-tenancy

Multi-tenancy enables multiple organisations (or 'tenants') to make use of the same software instance or physical infrastructure simultaneously. This could be at the storage, OS or application level and it's one of the key reasons cloud computing can be so economical. Security is strong as tenants' environment are kept completely separate to ensure no bleed between them, meaning data is secure.

A common issue with multi-tenancy cloud environments can be something called the "noisy neighbour" effect. Because resources are shared between tenants, performance can be unpredictable: if one organisation unexpectedly ramps up their usage for some reason, your performance may suffer. Good cloud providers will overcome this by provisioning an allocated amount of storage and compute to tenants, and decoupling storage from performance.

Public cloud

Public clouds are what most people imagine when they hear the term 'cloud computing'. They're shared pools of computing resources which exist on the premises of the cloud provider, delivering a range of free and paid-for services and infrastructure.

They are typically accessed on a self-service basis through a front-end portal, like a web-browser. The main advantage of a public cloud is the ability to scale-up your resources, almost infinitely, at peak times, and then quite easily scale back down when you no longer need them. The cost savings achieved from this move from CapEx to OpEx expenditure are substantial.

Security is often considered the biggest disadvantage to storing data in a public cloud environment. As the "cloud" doesn't reside within your four walls, but on the premises of a third party provider, there is the perception of a loss of control. Generally though, unless your data is highly sensitive, the level of security available through public cloud providers is usually more than adequate.

Other characteristics of public cloud are a lack of long-term commitment. The services should be rapidly elastic (though you may negotiate discounts for a commitment). Public clouds should also be self-service and charged on simple units such as per user or per GB.

Private cloud

Private clouds contain dedicated resources only accessible by a single organisation. They're tightly controlled and highly customisable. Organisations can tailor the environment very closely to their needs, to save costs and provision resources exactly where they're needed. Private clouds are particularly common in highly regulated organisations, where the security of sensitive data is crucial.

Whilst they don't necessarily need to be on-premise (private clouds can exist off-site in third party data centres and maintained through management portals), the organisation is still responsible for the configuration, maintenance and administration of their private environment. Private clouds allow for the highest levels visibility, security and control – you know exactly where your data is at all times. This enhanced level of security and control obviously comes with a higher price tag than the aforementioned public cloud, but is only really necessary for very sensitive data.

There is an argument that "private clouds" are not really clouds at all because they don't have the characteristics that we associate with cloud computing. You don't get to switch from CapEx to OpEx because you need to buy enough capacity to support your peak requirements and therefore you don't really have scalable flexibility.

Hybrid cloud

Hybrid cloud environments are a mix of public and private cloud services, distinct from one another and often procured from multiple sources.
Most organisations today possess very varied and complex needs from their cloud services, only some of which will demand the customisability and control of private clouds. As such, organisations may choose to separate the services they procure depending on their individual requirements and divide them between public and private environments accordingly.

Hybrid clouds are becoming an increasingly popular choice for many organisations because they can run the majority of their system in their private cloud, with the option to "burst" out into a public cloud at peak times. It's this flexibility and scalability that will see adoption of hybrid clouds continue to grow in 2015.