accessed via a local area network (LAN). This is due to the inherently unreliable network that is the Internet and the fact that as a managed service, Azure SQL Database might periodically undergo maintenance activities that could cause connections to temporarily drop. Applications should plan for, and defend against, transient errors by incorporating retry logic when creating connections or executing commands against Azure SQL Database. For .NET applications using Entity Framework, Entity Framework 6 contains connection resiliency/retry logic that will detect transient errors from Azure SQL Database and retry the command. For other .NET applications, Enterprise Library 5 and 6 (see http://msdn.microsoft.com/en-us/library/ff648951.aspx) from Microsoft Patterns & Practices contain an application block called the Transient Fault Handling Application Block. This library can also be used to detect transient errors and retry commands.
SQL Server in Azure Virtual Machines Whereas Azure SQL Database provides database-as-a-service with virtually no administration and with enterprise-grade features, there are still situations in which running your own SQL Server deployment is necessary. There are numerous reasons to host your own SQL Server deployment. A common reason is the requirement to use features that are not available in Azure SQL Database. As discussed in Chapter 3, Azure Virtual Machines provides the ability to host and manage your own VMs. What you use the VM for is largely your responsibility, and this includes using it to install, configure, and manage your own full SQL Server VM or cluster of VMs.
Billing When running your own SQL Server deployment on Azure Virtual Machines, there are three important cost factors to understand. First, there is the cost of the Windows VM itself. Recall that Azure VMs are charged on a per-minute usage model. Second, there is the SQL Server license cost. When using a SQL Server image from the Azure Virtual Machines image gallery, you will pay an additional per-minute SQL Server license cost, which varies according to the version of SQL Server (Web, Standard, or Enterprise) and the target size of the VM. Finally, you will also pay for the Azure Storage cost. Azure Storage (specifically page blobs) is used as the persistence mechanism for Azure Virtual Machines disks. To summarize, the cost for SQL Server in Azure Virtual Machines can be represented as Total Cost = Windows Server cost + SQL Server license cost + Azure Storage cost. If you have your own SQL Server license, you can use that instead of paying the per-minute charge associated with using a SQL Server license obtained from an Azure Virtual Machines image. In this case, you pay only for the Windows Server license and any related Azure Storage costs. The ability to use your own SQL Server license is a feature of License Mobility through Microsoft’s Software Assurance on Azure program. For more information, see http://azure.microsoft.com/pricing/license-mobility/.
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