Cloud Computing - Service and Deployment Models

Cloud service models are generally classified based on the type of resources shared: SaaS (Software as a Service), PaaS (Platform as a Service) and IaaS (Infrastructure as a Service). Cloud deployment models include public, private, hybrid and community cloud models. 

Cloud Service Models

IaaS (stands for Infrastructure as a Service)

The type of resources shared in IaaS mainly includes physical servers, virtual machines, load balancers, IP addresses and virtual local area networks (VLANs); but often also includes other resources such as a virtual-machine disk image library, raw (block) and file-based storage, firewalls and even software bundles.

PaaS (stands for Platform as a Service)

The type of resource shared in PaaS is usually a computing platform, typically including operating system, programming language execution environment, database, and web server. 

With some PaaS offerings, the underlying computer and storage resources scale automatically to match application demand so that the cloud user does not have to allocate resources manually.

Examples include Amazon EC2, Windows Azure, force.com from salesforce and Google App Engine.

The iPaaS, which stands for integration Platform as a Service, is a sub type of PaaS and deals with integrating various cloud technologies. Examples of iPaas include Dell Boomi AtomSphere from Dell and CloudStreams from Software AG. 

SaaS (stands for Software as a Service)

The type of resource shared in SaaS includes application software and databases. Cloud providers manage the infrastructure and platforms that run the applications. SaaS is sometimes referred to as "on-demand software" and is usually priced on a pay-per-use basis. SaaS providers generally price applications using a subscription fee.

Examples includes Salesforce CRM, SuccessFactors, Office 365 from Microsoft, Ariba Buyer On Demand and most Google services such as Gmail, Google Apps etc. 

Cloud Deployment Models

Cloud deployment models include public, private, hybrid and community cloud models. 

When a cloud service is available to everyone over the internet it is called a public cloud.

A private cloud is available only to a single client or a limited number of users and can be setup on-premises within the company firewall or off-premises. 

A Virtual Private Cloud (VPC) is a private cloud built using shared computing resources allocated within a public cloud environment. 

Managed Private Cloud refers to a principle where a private cloud serving a single client organization (tenant), and managed by a third-party. This is in contrast to multi-tenancy where multiple client organizations are on a single server.

A Hybrid Cloud combines the services of multiple clouds such as public and private clouds. Secured applications and data may be shared on a private cloud whereas shared applications and data may be stored on public clouds for cost effectiveness.

There may be also Community Cloud deployment models where services may be shared by organizations that have the same policy and compliance considerations.