Windows Azure virtual machines goes at least once a month for guest OS update and similarly Host OS update. Because of it the Windows Azure virtual machine, in which your application in running, will part of guest or host OS update and will be down for a few minutes per month during those update process. Besides these scheduled update it is possible your virtual machine may be down for other potential reasons. In other words you can case, the Windows Azure virtual machines uptime can be interrupted due to any reason and here we will see what the potential reasons are which can interrupt the virtual machine uptime.
Instance uptime interruption: A virtual machine Instance uptime is considered the amount of time virtual machine instance is running without interruption. This could be impacted due the following two reasons:
Instance re-Initialization: Instance re-Initialization is considered a process in which your instance is re-initialized with a clean VHD for given VM Role. For VM role, Instance Re-Initialization could happen in following few situations:
Thanks to Windows Azure Team for providing this information.