There are two types of downtime that can impact the availability of Azure virtual machine, and we should consider both planned and unplanned downtime, when discussing virtual machine availability:
Planned: Microsoft will advise planned downtime. These events happen from time to time as a result of updates made by Microsoft to the underlying Azure platform. There could be a variety of different reasons but would normally involve some changes being made to the underlying infrastructure that the virtual machine is running on. These events don't necessarily mean an outage to the virtual machine; it's possible that the changes will have no impact on the uptime of your virtual machine. However, if a situation arises whereby the changes made require a restart or reboot of the virtual machine, then you are still going to get an outage for that virtual machine. Whether that impacts your application availability will depend on your Azure virtual machine...
