Why are my Azure VMs not rebooting during maintenance windows?

Why are my Azure VMs not rebooting during maintenance windows?

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.

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