What is public cloud?
Public cloud is a multi-tenant cloud computing model in which shared infrastructure and services are delivered over the internet by third-party providers, including Microsoft Azure, Amazon Web Services (AWS) and Google Cloud. Resources are drawn from large shared pools, can generally be provisioned quickly and are adjusted according to demand.
What is private cloud?
Private cloud is a cloud environment in which the servers, storage and networking are allocated exclusively to a single organisation. It can be hosted in a provider’s datacentre or in your own facilities, and managed by you or by a provider. Our insight on What is Private Cloud? covers this in more detail.
What are the key differences between public and private cloud?
Resources and architecture
The ownership of the underlying infrastructure is the key difference. Public cloud uses a multi-tenant model, in which physical servers are virtualised, often using a hypervisor, and computing resources are shared between multiple customers. Private cloud uses a single-tenant model, where the physical hardware is dedicated to one organisation. Virtualisation is still used, but all virtual machines and resources stay within that organisation’s private environment.
Security and compliance
Environments within public cloud are logically isolated from one another, and the major providers invest heavily in security and hold extensive compliance certifications. As with any cloud, security is a shared responsibility, so customers remain responsible for how their own environment is configured and accessed.
Private cloud adds physical isolation, with exclusive access to the infrastructure and all virtual resources, and gives you more freedom to tailor your security suite and to choose where your data is hosted. This matters most for organisations with sensitive data or strict regulatory requirements, such as in healthcare and finance, where requirements may call for dedicated infrastructure or a specific hosting location. Our insight on compliance and sovereignty in private cloud covers this in more detail.
Scalability and flexibility
Both models scale through virtualisation and containerisation, with virtual resources added and removed as needed. Public cloud draws on very large shared pools, so it can provision new resources quickly and suits workloads with highly variable or short-lived demand. In a private cloud, resources are adjusted within the capacity of the platform, which is planned in advance, so it suits workloads whose demand you can forecast, including regular peaks such as Black Friday.
Cost and billing
The difference generally lies in the billing model. Public cloud is typically charged by consumption, sometimes by the minute of compute time or the gigabyte of storage, which suits variable workloads but can be hard to predict as usage and services change, and unused or oversized resources add to the bill. Private cloud typically offers a fixed monthly cost, which makes budgeting more predictable and suits steady workloads. Which works out cheaper depends on the workload, so compare the total cost over the lifetime of the infrastructure.
Management and control
Public cloud needs ongoing management, with configuration, access controls, monitoring and cost optimisation all needing attention, although a managed service can take much of this on. Private cloud gives you direct control over how the platform is built and configured, and the same kind of managed support is available.
Which workloads suit each model?
Public cloud is often chosen for:
- Workloads with variable or short-lived demand
- Development and testing environments
- Fast-scaling projects
- Applications that depend on particular platform services
- Less sensitive data
Private cloud is often chosen for:
- Workloads with steady, predictable demand
- Sensitive or regulated data
- Performance-critical applications
- Requirements for a specific configuration, certification or hosting location
- Private environments for AI workloads
The right fit depends on what the workload needs, whatever the size of the organisation.
Can you use both?
No cloud model is universally better than another. Many organisations place each workload where it suits best, using private cloud for steady or sensitive workloads and public cloud for variable ones.
Workloads in public cloud can be managed alongside those in private cloud. Managed public cloud helps you get more from AWS, Azure and Google Cloud, with engineers handling architecture, security, monitoring and optimisation. Enterprise cloud offers a further option, a logically isolated environment on shared infrastructure, for organisations that want isolation without dedicated hardware.
Moving between models is also easier than it was, with switching rights under the EU Data Act and commitments from AWS and Microsoft in the UK.
How do you choose between public and private cloud?
Questions worth asking include:
- How sensitive is your data, and which regulations apply?
- How variable is your demand, and how predictable do your costs need to be?
- Do you need specific hosting locations or certifications?
- How much control do you need over configuration?
- Who will manage the environment day to day?
- How easily could you move workloads in future?
Considering these requirements early helps ensure the platform can support both current workloads and future growth.
The next steps
Public and private cloud solve different problems, and for many organisations the answer is a combination, with each workload placed where it performs and costs best. Understanding the differences is the first step.
If you are deciding between them, speaking with an experienced managed hosting provider can help. Speak to one of our Cloud Consultants about your requirements, or explore our Managed Private Cloud and Managed Public Cloud options.
