Virtualisation has led to the growth of cloud computing, which in turn takes many forms.

At its root are powerful servers running in datacentres, which are the workhorses of the cloud. They provide the underlying power needed to run resources like VMs, virtual networks, and cloud storage.

But who owns these datacentres, and who is responsible for securing and maintain the hardware? It’s not a simple answer, and there are various models of cloud computing.

Pyramid diagram showing Cloud service models: SaaS- Software as a Service; PaaS- Platform as a Service; IaaS- Infrastructure as a Service.

Figure 1: Cloud service models

Four cloud models

Here’s an overview of four common ones: public, private, community and hybrid.

What’s a public cloud?

This is what people usually think of when it comes to cloud computing. You, the customer, pay a third party to use their cloud services. The cloud provider owns, runs and maintains the hardware and infrastructure needed for the cloud, and you’re a bit like a tenant paying rent.

And, like a shared office building, lots of other tenants use this cloud. You access this kind of cloud through a secure network connection, typically over the internet. Costs are usually calculated on a subscription or pay-as-you-use basis.

What’s a private cloud?

Sometimes an organisation creates a cloud environment in their own datacentre – this is a private cloud. The organisation is responsible for operating the services they provide, and access is not given to users outside the organisation.

This gives the organisation more flexibility than a public cloud, as they can design it to do exactly what they want. You’d want this kind of cloud for government agencies or financial institutions that need that deeper level of control or are subject to certain regulations.

What’s a community cloud?

A group of organisations with a common goal or focus may decide to share a cloud environment. This is called a community cloud. The underlying infrastructure could be managed internally or by a third party, and the costs are spread across the users.

A community cloud can be cheaper than using a private cloud as costs are shared. It’s also useful for organisations that may share industry specific regulatory or security requirements or need greater availability and control than a public cloud offers.

What’s a hybrid cloud?

This combines features of public and private clouds to allow applications to run in the most appropriate locations. This lets organisations get the benefits that come with public clouds like cost, efficiency, and scale, but they might also need a private cloud if they have greater security needs, so they combine the two together.

This means that they’ll be running their private cloud infrastructure on premises, while paying for the services of a public cloud as well. Technical skills are required here to maintain the private cloud and make sure both cloud models can operate together.

Levels of cloud service

The most popular cloud model is public, and you’re probably familiar with public cloud providers like AWS or Azure. But public clouds are not one size fits all. Depending on the level of service you choose, you will have varying levels of control over what you build. But with greater control also comes greater responsibility in terms of what you need to manage and secure.

Here’s breakdown of the three levels of cloud service, and what you manage at each:

Infrastructure as a Service (IaaS)

The cloud provider is responsible for maintaining the underlying hardware and network, while the user has control over deploying VMs, installing and managing the OS as well as any applications they want to use and some networking components such as host firewalls. They are also responsible for securing their data and controlling access.

This service could be used by an organisation that wants to ‘lift and shift’ its on-premises set-up into the cloud.

Platform as a Service (PaaS)

The cloud provider is responsible not just for the hardware infrastructure but also for running the VMs and OS. The user has control over the deployed applications and possibly configuration settings for the application-hosting environment.

This service might be used to develop and test new applications without having to worry about configuring the underlying OS.

Software as a Service (SaaS)

The cloud provider is responsible for the hardware, VMs, operating system, and applications. The customer uses the applications but doesn’t maintain them in any way. They do have access to limited user-specific application configuration settings.

An example of this is something like Office365 that allows organisations to give employees access to a suite of office apps via web browser.

Cloud model and cloud services recap

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