web角色是承载多个网站的虚拟机

Azure Web Sites enables you to build highly scalable web sites quickly on Azure. You can use the Azure Portal or the command-line tools to set up a web site with popular languages such as .NET, PHP, Node.js, and Python. Supported frameworks are already deployed and do not require more installation steps. The Azure Web Sites gallery contains many third-party applications, such as Drupal and WordPress as well as development frameworks such as Django and CakePHP. After creating a site, you can either migrate an existing web site or build a completely new web site. Web Sites eliminates the need to manage the physical hardware, and it also provides several scaling options. You can move from a shared multi-tenant model to a standard mode where dedicated machines service incoming traffic. Web Sites also enable you to integrate with other Azure services, such as SQL Database, Service Bus, and Storage. Using the Azure WebJobs SDK preview, you can add background processing. In summary, Azure Web Sites make it easier to focus on application development by supporting a wide range of languages, open source applications, and deployment methodologies (FTP, Git, Web Deploy, or TFS). If you don’t have specialized requirements that require Cloud Services or Virtual Machines, an Azure Web Site is most likely the best choice.

Cloud Services enable you to create highly-available, scalable web applications in a rich Platform as a Service (PaaS) environment. Unlike Web Sites, a cloud service is created first in a development environment, such as Visual Studio, before being deployed to Azure. Frameworks, such as PHP, require custom deployment steps or tasks that install the framework on role startup. The main advantage of Cloud Services is the ability to support more complex multitier architectures. A single cloud service could consist of a frontend web role and one or more worker roles. Each tier can be scaled independently. There is also an increased level of control over your web application infrastructure. For example, you can remote desktop onto the machines that are running the role instances. You can also script more advanced IIS and machine configuration changes that run at role startup, including tasks that require administrator control.

Virtual Machines enable you to run web applications on virtual machines in Azure. This capability is also known as Infrastructure as a Service (IaaS). Create new Windows Server or Linux machines through the portal, or upload an existing virtual machine image. Virtual Machines give you the most control over the operating system, configuration, and installed software and services. This is a good option for quickly migrating complex on-premises web applications to the cloud, because the machines can be moved as a whole. With Virtual Networks, you can also connect these virtual machines to on-premises corporate networks. As with Cloud Services, you have remote access to these machines and the ability to perform configuration changes at the administrative level. However, unlike Web Sites and Cloud Services, you must manage your virtual machine images and application architecture completely at the infrastructure level. One basic example is that you have to apply your own patches to the operating system.

从这个链接可以看到更新的和全面的比较:http://azure.microsoft.com/en-us/documentation/articles/choose-web-site-cloud-service-vm/

web角色是承载多个网站的虚拟机

Azure Web角色就像一个虚拟的私有主机。你有一个虚拟机作为你的web服务器，你拥有这个虚拟机实例。

Azure Web站点就像一个弹性共享托管服务。你把你的应用程序部署到一个不受你控制的web服务器上，它也为其他用户的网站提供服务。您可以根据资源需求的变化，上下扩展站点(需要额外付费)，使其更具弹性。

Azure网站、Web worker和虚拟机是Windows Azure上可用的三种不同的计算方法。他们在控制和责任的水平上有所不同:

Azure网站有最低级别的控制，但你不关心保持健康的虚拟机和IIS，因为Azure的东西为你做这些 Web角色给你更多的控制(流量管理器，远程桌面)，但更多的管理是可能的，这意味着你可以通过远程桌面破坏一些东西 虚拟机让您完全控制VM，因此需要最大的管理工作。

没有最好的选择，因为这取决于你需要什么样的控制级别，你需要什么特性，以及你希望留给Azure哪些东西来维护。这是一个大话题。

请阅读这篇文章，了解更多信息，做出更明智的选择:

http://www.windowsazure.com/en-us/documentation/articles/choose-web-site-cloud-service-vm/ http://davidpallmann.blogspot.com/2012/06/reintroducing-windows-azure-part-2.html

这可以归结为易用性和功能之间的权衡。

这是一个常见的问题，我想从msdn中摘录一段。

访问服务，如缓存，服务总线，存储，SQL Azure数据库-网站:是WebRole:是

支持ASP。NET，经典ASP, Node.js, PHP-网站:是WebRole:是

共享的内容和配置-网站:是WebRole:否

使用GIT、FTP部署代码-网站:是WebRole:否

近即时部署-网站:是web brole:否

集成mysql即服务支持-网站:是WebRole:是

多部署环境(生产和登台)-网站:没有WebRole:有

网络隔离-网站:无web brole:有

远程桌面访问服务器-网站:没有WebRole:是

能够以更高的权限运行程序-网站:没有web brole:是

能够定义/执行启动任务-网站:没有web brole:有

能够使用不受支持的框架或库-网站:没有WebRole:有

支持Windows Azure Connect/ Windows Azure Network-WebSite:No WebRole:Yes

要获得更多详细信息，请访问这个链接:http://blogs.msdn.com/b/silverlining/archive/2012/06/27/windows-azure-websites-web-roles-and-vms-when-to-use-which.aspx