With Exchange Server 2013, you can configure your mailbox databases in a database availability group (DAG) for automatic datacenter failover. This requires three separate physical locations: two datacenters for mailbox servers and a third location to place the witness server for the DAG. If your organization has three or more physical sites, this is easily done with existing infrastructure and the wide area network links that connect them.
If your organization has only two physical locations, you can now take advantage of the recently-added multi-site support of Microsoft Azure virtual networks. This new feature allows you to create an Azure virtual network that hosts the DAG witness server and has site-to-site VPN connections to both of your physical locations.
Here is an example configuration.
This Azure virtual network has two site-to-site VPN connections (one to Site A and another to Site B) and contains a replica domain controller and the witness server. Note that the Azure virtual network is not hosting an Exchange server. At this time, Microsoft does not recommend or support the hosting of production Exchange servers in an Azure virtual network.
See Using a Microsoft Azure VM as a DAG witness server for the details.
This is a great example of using Azure to help fill in the blanks of an infrastructure and enable a solution that is not otherwise possible.
If you have questions, or if you’d like to join the SAB, email us at SAB@microsoft.com.