Q. I've noticed that during Azure maintenance windows my VMs do not reboot but seem to simply pause then resume, what is happening?
Dept - Azure
A. When the Azure hosts require patching they leverage a technology called VM-PHU (Preserving Host Update). This technology enables the hosts to reboot from a new image (that has the patches applied) while keeping the VM state still in memory which means they essentially pause which is also known as in-place updates. Once the reboot completes the VMs are resumed and continue to perform their actions. This whole process is less than a minute and means VMs no longer go through a full reboot and are simply paused. The only time VMs will go through a full reboot is when VM-PHU cannot be used such as a major host change, for example a host OS upgrade to new version.
