Microsoft Azure periodically performs global updates in order to improve the reliability, performance, and security of the host infrastructure that underlies virtual machines. Sometimes this maintenance will cause your virtual machine to restart.
If you want to know if your VM rebooted because of planned maintenance you can check out the VM reboot logs in portal. This is found by going to the Cloud Service Workspace, opening up the dashboard for the cloud service, and clicking on the View Reboot Logs in the quick glance section.
Alternatively, if you prefer, you can use Azure PowerShell to get the same information:
Here’s a sample output of what you may see below.
You can learn more about getting these reboot logs here.