As you are aware, Windows Server 2008 R2 and SQL Server 2008/2008 R2 are reaching their end of life.
Microsoft has offered to extend the support of these products if you moved them to Azure for an additional 3 years to give more time for migration.
That said, once you have move your SQL Server 2008/2008 R2 workloads on Azure you still have to maintain and manage it, which means backing up your data.
If you moved these workloads to Azure, there is a good chance you also using Azure Recovery Services (ASR) and/or Azure Backup and you may want to leverage it backup these SQL 2008/2008 R2 workloads.
Well, the support for SQL 2008/2008 R2 by Azure Backup is now in preview.
During the preview period, the service is free of charge but once in general availability you will be charged the regular price (https://azure.microsoft.com/en-us/pricing/details/backup/)
There are few requirements before you can start using Azure Backup for SQL 2008/2008 R2:
- SQL Server 2008 and SQL Server 2008 R2 running on Windows 2008 R2 SP1
- .NET Framework 4.5.2 and above needs to be installed on the VM
- Backup for FCI and mirrored databases isn’t supported
In addition of the other limitations https://docs.microsoft.com/en-us/azure/backup/backup-azure-sql-database#feature-consideration-and-limitations