All those VMs that you use in Azure have to run on a host. At the moment, the majority of these hosts are running Windows Server 2012 R2. With Server 2016 now being available that include a range of additional features and functionality Microsoft is going to up updating the host machines in its datacenters to Server 2016 over the coming months.
This video will give you some good guidance on what to expect during the process for you VMs currently hosted in Azure. Chances are it will mean a reboot of your VMs but you’ll get plenty of notice beforehand and it is something that you should undertake manually anyway to complete the migration process.
The video has lots of great info, so if you have VMs running in Azure, consider this a heads up for upcoming host maintenance for your machines.