VM Migration Failure Which Results the VM in "ERROR" State

Problem

Post live migration of VM, the Nova API/DB shows the VM status as ERROR, although the VM continues running successfully on the target hypervisor.

Environment

• Private Cloud Director Virtualization - v2025.4 and Higher

• Self-Hosted Private Cloud Director Virtualization - v2025.4 and Higher

• Componen: Compute Service

Cause

This issue occurs due to inconsistencies between the Nova database and the actual hypervisor state during/after migration. Different underlying issues can cause this problem. Below are the common causes:

• Stale file locks on storage volumes.

• Database state mismatch between Nova conductor and compute host.

• Scheduler exceptions (e.g., NoValidHost) after migration completes.

Diagnostics

1. Stale file locks on storage volumes

• Migration fails with volume/lock errors.

• The /var/log/pf9/ostackhost.log from the source compute host:

nova.virt.libvirt.volume.mount [REQUEST_ID service] [instance: INSTANCE_ID] Request to remove attachment (volume-[VOLUME_ID] from [MOUNTPOINT], but we don't think it's in use.

ERROR nova.virt.libvirt.driver [REQUEST_ID service] [instance: [INSTANCE_ID]] Failed to start libvirt guest: libvirt.libvirtError: internal error: qemu unexpectedly closed the monitor: [TIMESTAMP] qemu-system-x86_64: -device virtio-blk-pci,..... 
Failed to get shared "write" lock

• Confirm Cinder volume status:

$ openstack volume show <VOLUME_ID>

1. Database state mismatch between Nova and hypervisor

• The openstack server show reports ERROR or wrong hypervisor, but VM is running on a different host.

• The /var/log/pf9/ostackhost.log from the source compute host:

nova.exception_Remote.UnexpectedTaskStateError_Remote: Conflict updating instance [INSTANCE_ID]  Expected: {\'task_state\': [\'migrating\']}. Actual: {\'task_state\': None}\nTraceback (most recent call last):\n\n  File  "/var/lib/openstack/lib/python3.10/site-packages/nova/db/main/api.py", line 2368, in _instance_update\n    update_on_match(compare, raise NoRowsMatched("Zero rows matched for %d attempts"  attempts)\n\noslo_db.sqlalchemy.update_match.NoRowsMatched: Zero rows matched for 3 attempts

[TIMESTAMP] TRACE nova.compute.manager [instance:  [INSTANCE_ID]] nova.exception.UnexpectedTaskStateError: Conflict updating instance  [INSTANCE_ID]. Expected: {'task_state': ['migrating']}. Actual: {'task_state': None}

• Check Nova DB entry vs actual hypervisor:

$ openstack server show -c OS-EXT-SRV-ATTR:hypervisor_hostname <VM_ID>

• Verify if the VM is running on the above mentioned hypervisor and its state:

$ virsh list --all | grep <INSTANCE_ID>

For Self-Hosted Private Cloud Director only

1. Scheduler exceptions (e.g., NoValidHost) after migration

• Migration logs show NoValidHost, but VM still boots/migrates at the hypervisor level.

• The nova-scheduler logs :

$ kubectl logs <NOVA_SCHEDULER_POD> -n <NAMESPACE>
NoValidHost(reason="")\\n\\nnova.exception.NoValidHost: No valid host was found.

Resolution

To restore consistency and recover the VM:

• Set the VM state to Active

$ openstack server set --state active <VM_ID>

• Start the VM:

$ openstack server start <VM_ID>

Validation

• Confirm the VM is now in ACTIVE state:

$ openstack server show -c status <VM_ID> 
| status | ACTIVE |

• Ensure it is hosted correctly:

$ openstack server show -c OS-EXT-SRV-ATTR:hypervisor_hostname <VM_ID>

Additional Information

• This procedure is safe: it resets Nova’s recorded state without modifying VM disk or memory.

• Always validate using virsh command that the VM is running before resetting state.

• For frequent issues, investigate root causes in Nova conductor, scheduler, and Cinder logs.