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发表于 2011-12-21 08:42 |只看该作者 |倒序浏览

http://blogs.msdn.com/b/enterprise_application_architecture/archive/2011/04/08/styles-of-platform-as-a-service-paas.aspx <span style="color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">let's
go through common styles of Platform as a Service, where Google App
Engine, Windows Azure and Force.com are the big players in this space,
talking about strength and weaknesses in each style.

· Instance aPaaS:
Developers deploy application code to instances of virtual machines.
Windows Azure is the canonical example of instance aPaaS. Windows Azure
supports worker and Web roles that map directly to VM instances. Engine
Yard's AppCloud and Amazon Web Services' Elastic Beanstalk are other
examples of instance aPaaS.
· Framework aPaaS:
Provides an abstraction at the code or programming model level.
Developers deploy code conforming to the framework and let the platform
worry about deploying it onto compute nodes. Google App Engine, Heroku,
and VMforce are examples of framework aPaaS. App Engine abstracts server
instances away with Servlet or Common Gateway Interface (CGI) HTTP
request model and asynchronous task queues.
· Metadata aPaaS:
Developers create metadata in visual programming environments that is
interpreted by the aPaaS at runtime. Force.com is the canonical example
of a metadata aPaaS. Force.com abstracts away the concept of server and
physical database instances using metadata. WaveMaker, Cordys Business
Operations Platform, and Microsoft Visual Studio LightSwitch are other
examples of metadata aPaaS.
<span style="color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">

Strengths and weaknesses of framework aPaaS and Google App Engine include:
<span style="color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: Symbol; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Platform
and sandbox restrictions require significant application redesign, but
the restrictions guidedevelopers to scalable, cloud-friendly design
patterns.
· In
Google's current offering, the non-relational data storage model
requires a significant development mind-shift. However, existing
Java/Python skills and (some) familiar APIs are leveraged.
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Framework
PaaS is easily extended by adding new/alternative frameworks (e.g.,
adding a Structured Query Language (SQL) database to App Engine services
to give developers choice).
· Platform
components are chosen and optimized for Google's infrastructure
platform. Application server instances autoscale automatically in
response to demand.

· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">App
Engine features a low entry price point and fine-grained billing for
over-quota resource consumption, but no SLAs (in the current offering).
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Weaknesses
in App Engine's development experience include the lack of live
debugging (though debugging using a local development environment is
possible).

<span style="font-family: 'Arial','sans-serif'; color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">
Strengths and weaknesses of instance aPaaS and Windows Azure include:
<span style="color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: Symbol; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">
· The
most familiar and flexible programming model of the three, Windows
Azure allows developers to leverage existing .NET Framework programming
language and API skills. Windows Azure supports relational data on SQL
Azure, thus providing an easier on-ramp than framework aPaaS for
mainstream developers.
· As
an instance aPaaS, Windows Azure supports arbitrary Windows
executables, including programming language runtimes (e.g., VMs for
Java, PHP, or Ruby). This flexibility is a double-edged sword —
developers can skewer themselves by deploying cloud-unaware code that
consumes metered resources inefficiently due to traditional
anti-patterns and bad practices.
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Windows Azure provides a rich development life cycle environment that supports debugging and multiple test staging environments.
· Windows
Azure makes SLAs available for its compute, storage, Windows Azure
AppFabric, and content distribution network services. Microsoft offers
access to Windows Azure with a complex set of pricing models, including a
medium-level entry price point.
· Windows
Azure provides the thinnest abstraction over virtual machines.
Developers need to manage VM instances explicitly. But more direct
interaction with Windows OS and VMs offers more leverage of third-party
code than is possible with other aPaaS types. Windows Azure does not
autoscale resources automatically in response to demand; Microsoft
engages partners to provide autoscale functionality using Windows Azure
instance management APIs.

<span style="font-family: 'Arial','sans-serif'; color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">
Strengths and weaknesses of metadata aPaaS and Force.com include:
<span style="color: black; font-size: 13.5pt; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: Symbol; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;">
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Force.com applications can easily leverage salesforce.com customer relationship management (CRM) data.
· Point-and-click
programming and customization tools can be used by non-professional IT
developers, thus making professionals more productive. But the rapid
application development (RAD) model can create quality risks by
circumventing software development life cycle (SDLC) governance
processes. Force.com mitigates access control risk by managing access
privileges at the level of user/data type permissions rather than
leaving this to the discretion of individual applications.
· <span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">AppExchange is a mature marketplace for applications and extensions
· Lock-in
to proprietary technologies is available at many levels (language,
framework, container, and hosting lock-in). Proprietary technologies
mean the programming model and customization skills are non-transferable
to another platform.
· Access
to fine-grained resources is impossible in the current Force.com
offering, thus making a true price-by-consumption model infeasible.
Service-level agreements are not provided (beyond "Termination for
Cause" provision) for the Force.com environment.
<span style="color: black; mso-ascii-theme-font: minor-bidi; mso-fareast-font-family: 'Times New Roman'; mso-hansi-theme-font: minor-bidi; mso-bidi-font-family: Arial; mso-bidi-theme-font: minor-bidi;" lang="en">Organizations evaluating aPaaS should consider the following recommendations:
· Match
aPaaS style with your application platform strategy. Understand the
competencies, restrictions, and business model for each platform before
adopting. Each platform has a sweet spot; don't try to shoehorn an
unsuitable use case into an aPaaS offering.
· Extend
your legacy software modernization program to include cloud adoption.
Significant modernization to an application is an opportunity to rethink
its platform and architecture. This provides an entry point to
prototype PaaS offerings.
· Start
prototyping with aPaaS now. In this early-stage market, the devil is in
the details. Pick an application and discover how the details affect
your development processes.
· Innovative
PaaS vendors have reformed platforms around cloud architecture
characteristics. With new programming models and patterns, developers
can approach problems that are resistant to traditional application
architecture practices. Teams should invest in learning application
patterns suitable for distributed, unreliable, and asynchronous systems.

Conclusion:
Organizations should choose aPaaS providers in the context of their
cloud adoption and application platform strategies. More importantly,
they should choose the style of aPaaS that fits their project and
architecture goals. aPaaS comes in instance, framework, and metadata
styles that increase in abstraction and increase in programming model
changes required to use them. Google App Engine, Windows Azure, and
Force.com are leading examples of each style. If developers adopt cloud
without adopting programming model changes, their applications are not
going to fully exploit the power of cloud platforms.

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