in my kolla openstack env, using containerized chrony service to keep controller node and compute node time sync. and by default, the instance guest OS time would be synchronized once with host at instance boot time, but I donot know whether the guest OS system time could be always synchronized with the host. If the guest OS time would be slowed down or inconsistented with the host, how to fix such issue? use chrony or ntp?
1 Answers
According to https://ask.openstack.org/en/question/290/time-keeping-in-instances/, it should not be necessary to sync clocks on a guest instance if the host is syncing its clock. Apparently kvm defaults to the guest VMs using the host's RTC. So if the host is syncing its RTC, the guests should see the correct time.
On the other hand, if a guest VM does sync its clock to an external source, I would not expect it to affect the host, or other guest VMs running on the host1. So if the guest OS "doesn't know", there should be little harm2 in installing and running clock sync software anyway.
Given that you own the infrastructure, this is a case where it would not be harmful to do some experiments.
1 - That would be a security problem. Someone would have considered it.
2 - Just a few unnecessary network packets, CPU cycles, etc
Related