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[Bug 1984009] [NEW] libvirt live-migration fails when network MTU is different

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Tyler Stachecki <1984009@xxxxxxxxxxxxxxxxxx>
Date: Mon, 08 Aug 2022 21:23:48 -0000
Reply-to: Bug 1984009 <1984009@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx

Public bug reported:

After changing the MTU of an OpenStack network, attempting to live-migrate an existing instance fails with e.g.:
ERROR nova.virt.libvirt.driver [-] [instance: f3807b12-fa7e-4da8-a688-c5507fb66891] Live Migration failure: unsupported configuration: Target network card MTU 9000 does not match source 1500: libvirt.libvirtError: unsupported configuration: Target network card MTU 9000 does not match source 1500

Indeed, the MTU should not change as per:
https://bugzilla.redhat.com/show_bug.cgi?id=1623157

However, it should be the case that libvirt live-migration code should
retain the MTU specified in the source domain. If we do that, live-
migration still works.

** Affects: nova
     Importance: Undecided
     Assignee: Tyler Stachecki (tstachecki)
         Status: New

** Changed in: nova
     Assignee: (unassigned) => Tyler Stachecki (tstachecki)

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https://bugs.launchpad.net/bugs/1984009

Title:
  libvirt live-migration fails when network MTU is different

Status in OpenStack Compute (nova):
  New

Bug description:
  After changing the MTU of an OpenStack network, attempting to live-migrate an existing instance fails with e.g.:
  ERROR nova.virt.libvirt.driver [-] [instance: f3807b12-fa7e-4da8-a688-c5507fb66891] Live Migration failure: unsupported configuration: Target network card MTU 9000 does not match source 1500: libvirt.libvirtError: unsupported configuration: Target network card MTU 9000 does not match source 1500

  Indeed, the MTU should not change as per:
  https://bugzilla.redhat.com/show_bug.cgi?id=1623157

  However, it should be the case that libvirt live-migration code should
  retain the MTU specified in the source domain. If we do that, live-
  migration still works.

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