The AppFabric component is used to create access control and distribute messages across clouds and enterprises. It has a service-oriented architecture, and can be considered as the backbone of the Windows Azure platform. It provides connectivity and messaging among distributed applications. It also has the capabilities of integrating the applications and the business processes between cloud services and also between cloud services and global applications. 

The AppFabric component provides a development environment that is integrated with Visual Studio 2010.TheWindows Communication Foundation (WCF) services built in VS 2010 can be published on cloud from the Visual Studio design environment.

The two important services of AppFabric are as follows:

• Access Control Service (ACS) - Allows rules-driven and claims-based access control for distributed applications. These claims-based rules and authorization roles can be defined in the cloud for accessing on-premise and cloud services. The claim can be a user or application attribute, which the service application expects, such as e-mail address, phone number, password, and role, for appropriate access control. When any application wants to use the Web service, it sends the required claims to ACS for requesting a token. ACS converts the input claims into output claims by following the rules of mapping. These rules are created during the configuration of ACS. The ACS issues a token containing the output claims for the consumer application. This application uses this token in the request header and sends to the Web service. This service validates the claims in the token and gives suitable access to the user.
• Service bus - Provides messaging between cross-enterprise and cross-cloud scenarios. It provides publish/subscribe, point-to-point, and queues message patterns for exchange of messages across distributed applications in the cloud. It integrates with the Access Control service to establish secure relay and communication.