Conventional wisdom holds that private clouds are better for workloads that have high compliance or security needs. Public cloud, meanwhile, is said to be ideal for almost anything else. That logic no longer applies quite so neatly. Both public and private cloud options have expanded in recent years, and the use cases for each model are not as clearly delineated as they once were. To decide whether public or private cloud is best for a given workload, consider these factors and nuances.
Public cloud vs. private cloud: How they compare
A public cloud provider makes storage, virtual machines and other services available over the internet to anyone who wants them. Although workloads are isolated at the software level, they run on shared infrastructure.
A private cloud, by comparison, offers cloud-based services only to select users -- typically, those within a certain organization. Traditionally, private clouds run on infrastructure owned by that organization, although services such as Amazon Virtual Private Cloud now enable customers to build private clouds using public cloud data centers.
In general, public clouds and private clouds provide the same types of services. The crucial differences lie in who can access the services and who owns the infrastructure that hosts them.
Five factors to consider when choosing public or private cloud
While the differences may seem relatively minor, they evoke several important considerations that affect whether a workload is a good candidate for public or private cloud.
- Expense model. Public cloud services are typically priced on a pay-as-you-go model. They therefore require no major upfront investment or capital expense, but an organization must carefully monitor cloud spending to avoid racking up big monthly charges. In contrast, a private cloud typically requires private infrastructure to host it, meaning an organization makes a large upfront investment. The tradeoff for the higher capital expense associated with private cloud is a lower ongoing operating expense.
- Range of cloud services. Most of the core services consumed by public cloud users, such as data storage, virtual machines and serverless functions, are available in private clouds as well. Modern public clouds, however, also provide certain niche services that don't yet have established, prebuilt equivalents on private cloud platforms. Without services from a public cloud provider, for example, it would be much more difficult to attempt machine learning or IoT initiatives.
- Compliance and security. In the early days of cloud adoption, many organizations believed that only private clouds could meet strict compliance and security requirements because they provide more control over services and the cloud infrastructure that hosts them. In most cases, that's no longer true. Public clouds now offer sophisticated methods to isolate workloads within specific geographic regions and manage sensitive data. In addition, most modern compliance frameworks, including the European Union's GDPR and the California Consumer Privacy Act, were written with the cloud in mind. It's entirely possible to remain compliant with these rules while running workloads in the cloud. That said, when you evaluate public cloud vs. private cloud, understand that private clouds still offer more fine-grained control over how cloud workloads are configured and hosted. This can make it easier to meet tight compliance or information security needs. For example, you could configure a private cloud in such a way that data never leaves a local data center, thereby avoiding compliance requirements that apply only when data moves off site.
- Performance. Because public clouds rely on the public internet to deliver services, their weakest performance link is the limitation on internet bandwidth and connectivity. In particular, workloads that require extensive data transfers will be delayed when they run in a public cloud. You can expect high performance and high reliability from private clouds in which computing resources are hosted and consumed in the same local site. They can rely on local networks, which are generally faster than public internet connections. Whichever path you choose, you'll need to prepare your network so that it is ready for a cloud environment.
- Manageability. Users must devote significant effort to set up and manage workloads, whether the workloads run in public or private clouds. A public cloud, however, entails less management effort because the service provider not only delivers the computing resources but also manages the hardware for you, such as an infrastructure-as-a-service model. With a private cloud in your own data center, the burden to maintain that hardware is yours.
Public? Private? Or a third option?
When considering your public cloud versus private cloud options, remember that one is not universally better than the other. But they are different. Private cloud computing generally offers greater control and lower ongoing costs, although it requires higher capital expenses and may not offer the variety of services that have helped make public cloud increasingly popular.
If you are struggling to choose between public and private cloud, a third option is hybrid cloud, which involves running public cloud services on private cloud infrastructure. Over the past few years, platforms such as Azure Stack, Google Anthos and AWS Outposts have emerged to make it fairly easy to deploy public cloud services on your own infrastructure. This approach might be particularly compelling for organizations that want the best of both worlds.