|By Thomas Erl||
|August 1, 2010 05:45 PM EDT||
For a complete list of the co-authors and contributors, see the end of the article.
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 , Redundant Implementation , State Repository , and Stateful Services . 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
- 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.
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.
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
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.
Other Deployment Models
There are variations of the previously discussed deployment models that are also worth noting. The hybrid cloud, for example, refers to a model comprised of both private and public cloud environments. The dedicated cloud (also known as the hosted cloud or virtual private cloud) represents cloud computing environments hosted and managed off-premise or in public cloud environments, but dedicated resources are provisioned solely for an organization's private use.
The Intercloud (Cloud of Clouds)
The intercloud is not as much a deployment model as it is a concept based on the aggregation of deployed clouds (Figure 8.1). Just like the Internet, which is a network of networks; intercloud refers to an inter-connected global cloud of clouds. Also like the World Wide Web, intercloud represents a massive collection of services that organizations can explore and consume.
Figure 1: Examples of how vendors establish a commercial intercloud
From a services consumption perspective, we can look at the intercloud as an on-demand SOA environment where useful services managed by other organizations can be leveraged and composed. In other words, services that are outside of an organization's own boundaries and operated and managed by others can become a part of the aggregate portfolio of services of those same organizations.
Deployment Models and Windows Azure
Windows Azure exists in a public cloud. Windows Azure itself is not made available as a packaged software product for organizations to deploy into their own IT enterprises. However, Windows Azure-related features and extensions exist in Microsoft's on-premise software products, and are collectively part of Microsoft's private cloud strategy. It is important to understand that even though the software infrastructure that runs Microsoft's public cloud and private clouds are different, layers that matter to end-user organizations, such as management, security, integration, data, and application are increasingly consistent across private and public cloud environments.
Service Delivery Models
Many different types of services can be delivered in the various cloud deployment environments. Essentially, any IT resource or function can eventually be made available as a service. Although cloud-based ecosystems allow for a wide range of service delivery models, three have become most prominent:
This service delivery model represents a modern form of utility computing and outsourced managed hosting. IaaS environments manage and provision fundamental computing resources (networking, storage, virtualized servers, etc.). This allows consumers to deploy and manage assets on leased or rented server instances, while the service providers own and govern the underlying infrastructure.
The PaaS model refers to an environment that provisions application platform resources to enable direct deployment of application-level assets (code, data, configurations, policies, etc.). This type of service generally operates at a higher abstraction level so that users manage and control the assets they deploy into these environments. With this arrangement, service providers maintain and govern the application environments, server instances, as well as the underlying infrastructure.
Hosted software applications or multi-tenant application services that end-users consume directly correspond to the SaaS delivery model. Consumers typically only have control over how they use the cloud-based service, while service providers maintain and govern the software, data, and underlying infrastructure.
Other Delivery Models
Cloud computing is not limited to the aforementioned delivery models. Security, governance, business process management, integration, complex event processing, information and data repository processing, collaborative processes-all can be exposed as services and consumed and utilized to create other services.
Note: Cloud deployment models and service delivery models are covered in more detail in the upcoming book SOA & Cloud Computing as part of the Prentice Hall Service-Oriented Computing Series from Thomas Erl. This book will also introduce several new design patterns related to cloud-based service, composition, and platform design.
IaaS vs. PaaS
In the context of SOA and developing cloud-based services with Windows Azure, we will focus primarily on IaaS and PaaS delivery models in this chapter. Figure 8.2 illustrates a helpful comparison that contrasts some primary differences. Basically, IaaS represents a separate environment to host the same assets that were traditionally hosted on-premise, whereas PaaS represents environments that can be leveraged to build and host next-generation service-oriented solutions.
Figure 2: Common Differentiations Between Delivery Models
We interact with PaaS at a higher abstraction level than with IaaS. This means we manage less of the infrastructure and assume simplified administration responsibilities. But at the same time, we have less control over this type of environment.
IaaS provides a similar infrastructure to traditional on-premise environments, but we may need to assume the responsibility to re-architect an application in order to effectively leverage platform service clouds. In the end, PaaS will generally achieve a higher level of scalability and reliability for hosted services.
An on-premise infrastructure is like having your own car. You have complete control over when and where you want to drive it, but you are also responsible for its operation and maintenance. IaaS is like using a car rental service. You still have control over when and where you want to go, but you don't need to be concerned with the vehicle's maintenance. PaaS is more comparable to public transportation. It is easier to use as you don't need to know how to operate it and it costs less. However, you don't have control over its operation, schedule, or routes.
- Cloud computing enables the delivery of scalable and available capabilities by leveraging dynamic and on-demand infrastructure.
- There are three common types of cloud deployment models: public cloud, private cloud, and community cloud.
- There are three common types of service delivery models: IaaS, PaaS, and SaaS.
• • •
This excerpt is from the book, "SOA with .NET & Windows Azure: Realizing Service-Orientation with the Microsoft Platform", edited and co-authored by Thomas Erl, with David Chou, John deVadoss, Nitin Ghandi, Hanu Kommapalati, Brian Loesgen, Christoph Schittko, Herbjörn Wilhelmsen, and Mickie Williams, with additional contributions from Scott Golightly, Daryl Hogan, Jeff King, and Scott Seely, published by Prentice Hall Professional, June 2010, ISBN 0131582313, Copyright 2010 SOA Systems Inc. For a complete Table of Contents please visit: www.informit.com/title/0131582313
David Chou is a technical architect at Microsoft and is based in Los Angeles. His focus is on collaborating with enterprises and organizations in such areas as cloud computing, SOA, Web, distributed systems, and security.
John deVadoss leads the Patterns & Practices team at Microsoft and is based in Redmond, WA.
Thomas Erl is the world's top-selling SOA author, series editor of the Prentice Hall Service-Oriented Computing Series from Thomas Erl (www.soabooks.com), and editor of the SOA Magazine (www.soamag.com).
Nitin Gandhi is an enterprise architect and an independent software consultant, based in Vancouver, BC.
Hanu Kommalapati is a Principal Platform Strategy Advisor for a Microsoft Developer and Platform Evangelism team based in North America.
Brian Loesgen is a Principal SOA Architect with Microsoft, based in San Diego. His extensive experience includes building sophisticated enterprise, ESB and SOA solutions.
Christoph Schittko is an architect for Microsoft, based in Texas. His focus is to work with customers to build innovative solutions that combine software + services for cutting edge user experiences and the leveraging of service-oriented architecture (SOA) solutions.
Herbjörn Wilhelmsen is a consultant at Forefront Consulting Group, based in Stockholm, Sweden. His main areas of focus are Service-Oriented Architecture, Cloud Computing and Business Architecture.
Mickey Williams leads the Technology Platform Group at Neudesic, based in Laguna Hills,
Scott Golightly is currently an Enterprise Solution Strategist with Advaiya, Inc; he is also a Microsoft Regional Director with more than 15 years of experience helping clients to create solutions to business problems with various technologies.
Darryl Hogan is an architect with more than 15 years experience in the IT industry. Darryl has gained significant practical experience during his career as a consultant, technical evangelist and architect.
As a Senior Technical Product Manager at Microsoft, Kris works with customers, partners, and industry analysts to ensure the next generation of Microsoft technology meets customers' requirements for building distributed, service-oriented solutions.
Jeff King has been working with the Windows Azure platform since its first announcement at PDC 2008 and works with Windows Azure early adopter customers in the Windows Azure TAP
Scott Seely is co-founder of Tech in the Middle, www.techinthemiddle.com, and president of Friseton, LLC,
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