As you probably know, TechEd Europe has been taking place in Barcelona this week. Among the various announcements and news snippets released this week is the juicy morsel revealed in a session covering High Availability and Site Resilience that Microsoft will support placement of the witness server for a Database Availability Group (DAG) in Azure from January 2015 onwards. No doubt a formal announcement will be published on the EHLO blog. For the moment, the only other detail that we know is that this is not the same as the "Windows Server 10 cloud witness feature."
Given that the session focused on Exchange 2013 SP1, I hazard a guess that this feature will require whatever the supported versions of Exchange 2013 are in January, namely Exchange 2013 CU6 and Exchange 2013 CU7 (assuming that ships inside the normal release window, which means relatively soon). Chances are that you won't be able to use an Azure witness server with an Exchange 2010 DAG, but you never know what the wizards of Redmond might allow.
Microsoft has been down this path before when they discussed the placement of a witness server in Azure at TechEd North America 2013. The idea was that Azure would provide an always-available location for the witness server that could be contacted by member servers in a DAG that stretched across multiple datacenters. Having a highly available witness server is a very good thing as it avoids scenarios like what happens when a datacenter that hosts the witness server goes offline and the server is needed to allow the DAG (and its underlying cluster) to maintain quorum.
After the due diligence and testing was complete, Microsoft determined that some networking changes were required within Azure to allow secure connections to the witness server from the customer datacenters that hosted the DAG member servers. It looks like the issues have been solved to allow the witness server to operate properly to maintain cluster quorum when required during datacenter outages.
Microsoft hasn't taken the step of allowing DAG member servers (or any other Exchange servers) to be deployed in Azure yet. At least, although you can deploy Exchange servers in Azure for test purposes, Microsoft will not support their use in production. And as has been pointed out, the economics of running Exchange servers on cloud-based platforms that charge based on resource usage might well make such a notion unattractive.
I'll be tracking developments in this space with some interest. You never know where it might lead!
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