Now that we know the essential characteristics of cloud computing, let's take a look at what kind of services are offered by cloud computing and how they are delivered.
Cloud computing services can be categorized into three service delivery models:
Software as a service (SaaS)
Platform as a Service (PaaS)
Infrastructure as a Service (IaaS)
SaaS allows the consumer of the service to use a specific functionality delivered by an application running in the cloud. Basically, this means consumption of cloud with no management involved. The consumer is not aware of and is not able to manage and adjust any of the components of application and infrastructure. There are many vendors offering SaaS solutions, for example Microsoft Office 365, Salesforce, and Google Apps.
PaaS offers the consumer a set of software tools to develop and publish applications over the Internet. The consumer, mostly software developers, do not have or need control over the infrastructure (networking, storage, and compute) but are able to manage at the application and data level.
IaaS gives the consumer the most amount of control of the three cloud computing delivery models. The provider offers a physical infrastructure that consists of compute, storage, and networking. The provider also manages the virtualization layer. The consumer can than manage workloads (operating system and applications) over which the consumer has full control. Microsoft Azure and Amazon EC2 are just two examples of many cloud IaaS services.
The following figure shows the three delivery models and their responsibilities:
Besides the three service delivery models that are mentioned here, there are many other XaaS offerings:
Desktop as a Service: This focuses solely on delivering cloud-hosted virtual desktops
Disaster Recovery as a Service: This delivers resources that can be temporarily used to host the IT infrastructure and services not available anymore in the primary location
Communication as a Service (CaaS): This is a rapid expanding service in which Voice over IP services and Unified Collaboration services is offered from the cloud
However, this book will fully focus on the IaaS part of Microsoft Azure. While Microsoft Azure started as a PaaS platform and most of its functionality was targeted at developers, Microsoft Azure IaaS has rapidly evolved towards a mature full infrastructure service offering.