Microsoft’s Software-plus-Services strategy represents a view of the world where the growing feature-set of devices and the increasing ubiquity of the Web are combined to deliver more compelling solutions. Software-plus-Services represents an evolutionary step that is based on existing best practices in IT and extends the application potential of core service-orientation design principles.

Microsoft’s efforts to embrace the Software-plus-Services vision are framed by three core goals:

• User experiences should span beyond a single device
• Solution architectures should be able to intelligently leverage and integrate
  on-premise IT assets with cloud assets
• Tightly coupled systems should give way to federations of cooperating systems and loosely coupled compositions

The Windows Azure platform represents one of the major components of the Software-plus-Services strategy, as Microsoft’s cloud computing operating environment, designed from the outset to holistically manage pools of computation, storage and networking; all encapsulated by one or more services.

Cloud Computing 101

Just like service-oriented computing, cloud computing is a term that represents many diverse perspectives and technologies. In this book, our focus is on cloud computing in relation to SOA and Windows Azure.

Cloud computing enables the delivery of scalable and available capabilities by leveraging dynamic and on-demand infrastructure. By leveraging these modern service technology advances and various pervasive Internet technologies, the “cloud” represents an abstraction of services and resources, such that the underlying complexities of the technical implementations are encapsulated and transparent from users and consumer programs interacting with the cloud.

At the most fundamental level, cloud computing impacts two aspects of how people interact with technologies today:

• How services are consumed
• How services are delivered

Although cloud computing was originally, and still often is, associated with Web-based applications that can be accessed by end-users via various devices, it is also very much about applications and services themselves being consumers of cloud-based services. This fundamental change is a result of the transformation brought about by the adoption of SOA and Web-based industry standards, allowing for service-oriented and Web-based resources to become universally accessible on the Internet as on-demand services.

One example has been an approach whereby programmatic access to popular functions on Web properties is provided by simplifying efforts at integrating public-facing services and resource-based interactions, often via RESTful interfaces. This was also termed “Web-oriented architecture” or “WOA,” and was considered a subset of SOA. Architectural views such as this assisted in establishing the Web-as-a-platform concept, and helped shed light on the increasing inter-connected potential of the Web as a massive collection (or cloud) of ready-to-use and always-available capabilities.

This view can fundamentally change the way services are designed and constructed, as we reuse not only someone else’s code and data, but also their infrastructure resources, and leverage them as part of our own service implementations. We do not need to understand the inner workings and technical details of these services; Service Abstraction (696), as a principle, is applied to its fullest extent by hiding implementation details behind clouds.

SOA Principles and Patterns

There are several SOA design patterns that are closely related to common cloud computing implementations, such as Decoupled Contract [735], Redundant Implementation [766], State Repository [785], and Stateful Services [786]. In this and subsequent chapters, these and other patterns will be explored as they apply specifically to the Windows Azure cloud ­platform.

With regards to service delivery, we are focused on the actual design, development, and implementation of cloud-based services. Let’s begin by establishing high-level characteristics that a cloud computing environment can include:

• Generally accessible
• Always available and highly reliable
• Elastic and scalable
• Abstract and modular resources
• Service-oriented
• Self-service management and simplified provisioning

Fundamental topics regarding service delivery pertain to the cloud deployment model used to provide the hosting environment and the service delivery model that represents the functional nature of a given cloud-based service. The next two sections explore these two types of models.

Cloud Deployment Models
There are three primary cloud deployment models. Each can exhibit the previously listed characteristics; their differences lie primarily in the scope and access of published cloud services, as they are made available to service consumers.

Let’s briefly discuss these deployment models individually.

Public Cloud
Also known as external cloud or multi-tenant cloud, this model essentially represents a cloud environment that is openly accessible. It generally provides an IT infrastructure in a third-party physical data center that can be utilized to deliver services without having to be concerned with the underlying technical complexities.

Essential characteristics of a public cloud typically include:

• Homogeneous infrastructure
• Common policies
• Shared resources and multi-tenant
• Leased or rented infrastructure; operational expenditure cost model
• Economies of scale and elastic scalability

Note that public clouds can host individual services or collections of services, allow for the deployment of service compositions, and even entire service inventories.

Private Cloud
Also referred to as internal cloud or on-premise cloud, a private cloud intentionally limits access to its resources to service consumers that belong to the same organization that owns the cloud. In other words, the infrastructure that is managed and operated for one organization only, primarily to maintain a consistent level of control over security, privacy, and governance.

Essential characteristics of a private cloud typically include:

• Heterogeneous infrastructure
• Customized and tailored policies
• Dedicated resources
• In-house infrastructure (capital expenditure cost model)
• End-to-end control

Community Cloud

This deployment model typically refers to special-purpose cloud computing environments shared and managed by a number of related organizations participating in a common domain or vertical market.