High Availability

High availability refers to providing business continuity when the physical server hosting Azure SQL Database fails.

As discussed in Lesson 1, Microsoft Azure SQL Database Primer, Azure SQL Database is hosted on three servers – one primary server and two secondary servers:

Figure 8.1: Azure SQL Database is hosted on three servers

The toyfactory database consists of three servers: one primary server and at least two secondary servers. The Azure SQL Server is just a logical server name used for connections. When an application sends a connection request, the gateway finds the current primary server and routes the request to it.

The primary and secondary servers are within the same data center and together form a quorum set.

All reads and writes are made to the primary server. Azure SQL Database uses a quorum-based commit method that makes sure that the data is hardened at the primary server and replicated to at least one secondary server before the transaction...