Live Migration

From PrgmrWiki

Live Migration

Live migration is a technique for moving a virtual machine between physical host servers without requiring a reboot. However, it is not supported equally well by all of the operating systems running on VPSes.

Operating Systems Known not to be Live-Migration Capable Under Xen

Neither NetBSD nor OpenBSD can be live-migrated under Xen. If you are running either of those, we will need to reboot your service to move it to a new host.

Versions of the Linux Kernel That Cannot Be Safely Live-migrated

A commit first appearing in version 4.11 of the Linux kernel broke Xen guest time handling across migration. Migrating a guest running an affected version of the Linux kernel could result in stalled network connections, an unresponsive VPS, inability to properly shut down the VPS, or incorrect timestamps in dmesg output. The only one of those symptoms that is guaranteed is incorrect timestamps in dmesg output, but the rest have been observed.

This issue was fixed in version 5.0.0 of the Linux kernel, and the fix was backported to older kernel series that were still under support. The following series received a backport:

  • 4.14: Fixed in version 4.14.97 or greater.
  • 4.19: Fixed in version 4.19.17 or greater.
  • 4.20: Fixed in version 4.20.4 or greater.

If your VPS is running a kernel with a version number greater or equal to 4.11.0 and less than 5.0.0 and the kernel didn't receive the backport mentioned above, you'll need to upgrade your kernel in order for us to be able to safely live-migrate your VPS. See below for a breakdown of upgrade paths for supported distributions. To check your kernel version, use the uname command:

$ uname -r

Known Kernel Upgrade Paths

  • CentOS 8: There is no upgrade path at this time; live-migrating CentOS 8 is unsafe.
  • Ubuntu Bionic 18.04: Install the package linux-image-5.0.0-15-generic.
  • Ubuntu Cosmic 18.10: There are no newer kernels available; your only option is to upgrade to Disco.
  • Fedora 28 and Fedora 29: Fixed by running `sudo dnf upgrade`; a 5.0.0 kernel is the latest available for both of these distributions.
  • Fedora 26 or Fedora 27: No options other than upgrading to a newer Fedora release.

If your kernel cannot be upgraded, or your operating system is otherwise incapable of being live-migrated, there are options to disable or enable live migration under the Maintenance Options submenu of the Management Console.