Public cloud services are available for anyone to subscribe to and use. The key benefit of a public cloud approach is one of scale – the cloud provider can potentially offer a better service at a lower cost because the scale of their operation means that they can afford the skilled people and state-of-the-art technology.
The public cloud model inherently provides service on demand. The cloud provider can dynamically reallocate resources as they are required. Spreading the service delivery across multiple locations also improves resilience. Local problems with power supplies, telecommunications, natural disasters, and so forth, can be managed more effectively when there are several datacentres in multiple geographies.The downside of the public cloud is the risks of compliance and data security. For example, data privacy laws in the EU mandate that personal data must be processed within defined guidelines. The cloud service customer, which is the “data controller”, is responsible in law, and needs to ensure that these guidelines are adhered to. Large cloud providers have recognised this need and can offer compliant services. Sharing applications and infrastructure with unknown co-tenants can lead to concerns over data security and data leakage. There are standards and best practices for this, and it is essential to check that the cloud provider is externally certified as adhering to these.
The HMRC online tax filing service is software-as-a-service with a public deployment model and this has been praised by the Audit Office, although it unclear whether it provides value for money.
A private cloud service is used exclusively by a single organisation. The private cloud allows organisations to outsource the management of their IT infrastructure while retaining tighter control over the location and management of the resources. The price to pay for this is that the costs are likely to be higher because there is less potential for economy of scale, and resilience may be lower because of the limit on service resources available.
Isolation is one of the key techniques for ensuring security and, while in the public cloud applications and data exist in a shared environment, the private cloud offers greater isolation by dedicating resources to a particular customer.
A community cloud service is for the exclusive use of a specific community of organisations that have shared concerns (e.g. mission, security requirements, policy, and compliance considerations). A community cloud provides many of the benefits of scale of the public cloud, while retaining greater control over compliance and data privacy.
Community cloud services already exist, but under a different name – for example NHSmail, the national e-mail and directory service available to NHS staff in England and Scotland, is effectively software-as-a-service with a community deployment model. As regards security, NHSmail is accredited to government "restricted" status, and is the only NHS e-mail service that is secure enough for the transmission of confidential patient information.
