Windows Azure SQL Database Architecture
Microsoft Windows Azure SQL Database is hosted on servers running SQL Server technologies in Microsoft data centers. From an architectural perspective, there are four distinct layers of abstraction that work together to provide a relational database for your application to use: the client layer, the services layer, the platform layer, and the infrastructure layer.
As seen in the following diagram, SQL Database works with third-party applications, open source, and many familiar Microsoft applications.
The Client Layer
The client layer resides closest to your application, and is used by your application to communicate directly with SQL Database. The client layer can reside on-premise in your datacenter or be hosted in Windows Azure. Because SQL Database provides the same tabular data stream (TDS) interface as SQL Server, you can use familiar tools and libraries to build client applications for data that is in the cloud.
There are many options available to your application for communicating with SQL Database. For more information about tools and driver support, see Tools and Utilities Support (Windows Azure SQL Database) and Guidelines and Limitations (Windows Azure SQL Database).
The Services Layer
The services layer functions as a gateway between the client layer and the platform layer, where the data resides. The services layer provides three functions: provisioning, billing and metering, and connection routing.
The services layer provisions the databases that you specify with your Windows Azure platform account. The billing and metering aspect of the services layer enables multi-tenant support by providing monitoring and billing for database usage based on individual Windows Azure platform accounts. SQL Database is built on a scalable platform involving numerous physical servers; this layer handles all the connections routing between your application and the physical servers where your data resides.
The Platform Layer
The platform layer includes the physical servers and services that support the services layer. The platform layer consists of many instances of SQL Server, each of which is managed by the SQL Database fabric.
The SQL Database fabric is a distributed computing system composed of tightly integrated networks, servers, and storage. It enables automatic failover, load balancing, and automatic replication between physical servers.
Management services monitor the health of individual servers and enable automated installation of service upgrades and software patches.
The infrastructure layer represents the IT administration of the physical hardware and operating systems that support the services layer.