what actions will trigger azure worker role reboot

Hi team,

we have a application host in worker role, the worker process will create a new process if it receive a request, 

i we want to update the worker and keep new process still working smoothly, what we should do during the Udate.

we did some test for this and found that when updating the worker role via portal, the worker role VM will not reboot, 

will all update not cause worker role reboot?

another question, what actions will cause worker role reboot,so that we could avoid them when doing update.

thanks in advance.