High Availability
High availability refers to providing business continuity when the physical server hosting the Azure SQL Database fails.
As discussed in Chapter 1, Microsoft Azure SQL Database Primer, an Azure SQL Database is hosted on three servers – one primary and two secondary servers:
The
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database consists of three servers; one primary and at least two secondary servers. The Azure SQL Server is just a logical server name used for connection. When an application sends a connection request, the gateway finds out the current primary server and routes the request to the primary server.
The primary and secondary servers are within the same datacentre and together form a quorum-set.
All read 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...