SQL Azure resides in Microsoft Data center provides relational database to application with four layer of abstraction.
Four layers of abstraction can be depicted as below,
This layer is closest to the application. SQL Azure connects with client application with Tabular Data Stream interface in exactly the same way SQL Server does.
Client layer can be ranging from a managed .NET application to PHP application. It could be a SilverLight web application or WCF Data Service. Client layers connect with other layers using Tabular Data Stream.
Client layer may be in client data center [On premise] or it may be in Data center of service provider [Cloud].
Service layer performs task of provisioning of database to the user cross ponding to Azure account. This mainly performs
a. Provisioning of Database to a Azure account
b. Billing of the usage
c. It performs the task of connection routing between client applications from the client layer to the actual physical SQL server in Platform layer.
Physically SQL Server resides in this layer. There could be many instances of SQL server.
SQL Azure Fabric manages instance of SQL Server.
Task performed by SQL Azure Fabric
1. It enables automatic failover
2. It does load balancing
3. It does automatic replication between physical servers.
Each instance of SQL Server is individually managed by SQL Azure Fabric.
Management Services performs below tasks,
1. Monitoring health of individual servers.
2. Installing patch up
3. Upgrading services
4. Automated installations
In this layer IT level administration tasks being performed. Physical hardware and operating systems is being administered in this layer.