What is Cloud Computing?

NIST official definition:

Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model is composed of five essential characteristics:

On-demand self-service, Broad network access, Resource pooling, Rapid elasticity or expansion, and Measured service.

It also lists three "service models" (software, platform and infrastructure), and four "deployment models" (private, community, public and hybrid) that together categorize ways to deliver cloud services.

Which Cloud model is right for You?

Public Cloud

In Public cloud the computing infrastructure is hosted by the cloud vendor at the vendor's premises. The customer has no visibility and control over where the computing infrastructure is hosted. The computing infrastructure is shared between many organizations.

Private Cloud

Private clouds are data center architectures owned by a single company that provides flexibility, scalability, provisioning, automation and monitoring.

Private clouds are driven by concerns around security and compliance, and keeping assets within the firewall.

Hybrid Cloud

Hybrid Cloud offers the "best-of-both-worlds". Organizations may host critical applications on their own private cloud and leverage the public cloud for applications with relatively less security concerns or for overflow during peak load times.

Cloud Computing layers...

As the cloud computing model gains in popularity it is important to understand the service layers that define it. Like the seven layer OSI model for networking, each layer of the cloud computing model exists conceptually on the foundation of the previous layers.

Within this model, there are three different service layers that are used to specify what is being provisioned, Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS).

Additionally, there are three further layers that are not provided as user services. The Hardware Layer and the Virtualization Layer are owned and operated of the cloud services provider while the Client Layer is supplied by the end users.