Public Cloud Vs Private Cloud: What's the difference?
A public cloud is an IT model where service providers, such as Amazon Web Services (AWS), Microsoft and Google make computing services, including compute and storage, develop-and-deploy environments, and applications, available on-demand. The term "on-demand" in this context means that these services are instantly available without any upfront investment.
In most cases, a public cloud service is multi-tenant, meaning that multiple end-users and customers share common elements of the IT model, such as the data centre and hardware. However, providers implement segregation controls through a shared responsibility model to ensure the security of each individual user and customer.
Anyone at this point who is concerned by the shared natured, should be assured that when used correctly, a public cloud is one of the most secure IT models available in the market.
Cloud computing began in the 1960s with vendors such as IBM and DEC promoting the idea of time-sharing, but it didn’t become popular with enterprises until the 1990s. The concept of a cloud computing model was created in 1996, with the first known mention in a Compaq internal document.
In 2006, Amazon launched its Elastic Compute Cloud (EC2) – an IaaS platform. Not long after, Google released Google App Engine, and Microsoft released Azure.
Gradually, all three established IaaS, PaaS and SaaS services. By 2012, IBM and Oracle had entered the market with similar applications.
Today, a variety of public cloud services and vendors are available to organisations. And the use of public clouds is still rising, with advancements in technology like AI and machine learning improving public cloud offerings.
As of 2022, Gartner recognises Amazon Web Services (AWS), Microsoft and Google as the market leaders.
These are the three main public cloud service models:
Software-as-a-service (SaaS) providers distribute software hosted in the cloud. Users can access this software through the internet, removing the need to install it on local devices and reducing the company’s IT costs. This removes all the traditional need for aspects such as application development, maintenance, backup, monitoring, patching etc.
Platform-as-a-service (PaaS) providers deliver turn-key components for use in overall solutions. This includes all the infrastructure and middleware (e.g. database management solutions) but typically still requires the user to perform functions such as backup, monitoring and patching.
Infrastructure-as-a-service (IaaS) providers deliver turn-key infrastructure, including all the datacentre, power, cooling, hardware and virtualisation. The user is still required to build and maintain virtual servers, operating systems and all associated functions such as backup, monitoring and patching.
There are various cloud models – public, private and hybrid – that suit businesses depending on their existing IT infrastructure, resources, requirements and more.
So, it’s important to understand the advantages and disadvantages of a chosen model before investing.
Cost savings: Migrating to a public cloud can save companies money by reducing IT costs. These costs are typically transitioned from large upfront CapEx investments to ongoing monthly OpEx payments.
But typically, the cost saving doesn’t originate from here. It instead comes from the cultural shift an organisation must go through to move to just-in-time provisioning (only use what you need) instead of designing and building for multiple years of expected growth. This has the added benefit of often being more sustainable (reduced carbon emissions) but can often be confusing as it is not a like-for-like comparison.
New technology: on-premises environments are often constrained by physical space, capacity or skills to explore new technology. Whereas public cloud offers on-demand, turn-key options for many advanced areas such as data analytics, machine learning, AI and security. These resources are also regularly and automatically updated and upgraded by the provider.
Scalability: Public Cloud offers somewhat unlimited capacity, allowing your IT to scale (up/down) with your business, but again, this is often the result of cultural and technology/application changes.
Runaway costs: costs can be complex and confusing due to the variety of pricing models. Businesses must implement robust governance to minimise over or shadow-spending, but even then, an organisation can be subject to variable changes when using an on-demand agreement.
Lock-in: some businesses, for example, retailers and logistics, view AWS as a competitor and, therefore, tend to favour Microsoft or Google. Others, perceive all three to present a level of lock-in; the deeper you go (PaaS and SaaS), the harder it is to exit. On balance, this is a valid point, but regardless of the underlying technology, exiting is always a complex process.
Security: this is often a concern many businesses will voice. Although the multitenancy model carries the risk of data leakage and a lack of control for businesses, many of the risks are similar whether the data is stored on-premises or in a public cloud. These risks include those resulting from inadequate technology configuration or human error.
Public cloud solutions are often used as part of a wider cloud strategy – typically ‘hybrid’ or ‘multi-cloud’ models.
As of 2022, in Flexera’s annual State of Cloud Report, 16% of respondents only use public cloud, whereas only 4% only use on-premises/private cloud and 56% using a combination of both (hybrid cloud).
The multi-cloud model is when a company uses more than one public cloud provider, which nearly all businesses do, for example, using SalesForce, Microsoft Office 365 and Amazon Web Services.
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