A public cloud is one based on the standard cloud computing model, in which a service provider makes resources, such as virtual machines (VMs), applications or storage, available to the general public over the internet. Public cloud services may be free or offered on a pay-per-usage model.
The main benefits of using a public cloud service are:
- it reduces the need for organizations to invest in and maintain their own on-premises IT resources;
- it enables scalability to meet workload and user demands; and
- there are fewer wasted resources because customers only pay for the resources they use.
Public cloud architecture
Public cloud is a fully virtualized environment. In addition, providers have a multi-tenant architecture that enables users -- or tenants -- to share computing resources. Each tenant's data in the public cloud, however, remains isolated from other tenants. Public cloud also relies on high-bandwidth network connectivity to rapidly transmit data.
Public cloud storage is typically redundant, using multiple data centers and careful replication of file versions. This characteristic has given it a reputation for resiliency.
Public cloud architecture can be further categorized by service model. Common service models include:
- software as a service (SaaS), in which a third-party provider hosts applications and makes them available to customers over the internet;
- platform as a service (PaaS), in which a third-party provider delivers hardware and software tools -- usually those needed for application development -- to its users as a service; and
- infrastructure as a service (IaaS), in which a third-party provider offers virtualized computing resources, such as VMs and storage, over the internet.
Public cloud vs. private cloud and hybrid cloud
The term public cloud arose to differentiate between the standard cloud computing model and the private cloud, which is a proprietary cloud computing architecture dedicated to a single organization. Private cloud differs from public cloud, as it serves as an extension of a company's existing data center and is accessible only by that company.