Time Synchronization for Guest VMs

Solution In Progress - Updated -

Issue

  • When spawning RHEL 7/8 and other guest VM (CentOS 7) operating systems into OpenStack we see that the VM clocks begin to time skew and we have observed up to 4 minute differences between VMs. From my understanding, KVM should be providing RTC synchronization for the guest operating systems, but it does not seem to keep them in any tight sync. We have confirmed that all of our controllers and compute nodes in Openstack are time synchronized with our NTP server and are within milliseconds of each other.

  • So is this an expected behavior and the guest VMs must be configured with an external NTP service or is there a way to configure the OpenStack KVM compute hosts to provide the appropriate timing to the guest VMs (not sure if a configuration is needed on the compute host via templates. the guest VM needs configuration before utilizing the RTC appropriately, both, or if this is simply not supported by Openstack)

Environment

  • Red Hat OpenStack Platform 16.1 (RHOSP)

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