Unable to Create Virtual Machine on Compute Host – Host Not Mapped to Any Cell

Problem

Virtual Machine creation fails with the following error:

Host '[HOST_UUID]' is not mapped to any cell

Environment

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

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

For Private Cloud Director (SaaS) users, if you encounter the same issue, please contact Platform9 Support.

Cause

The compute host was not properly mapped to any Nova cell. This can happen if:

• The host was added without triggering automatic cell discovery.

• The host was removed or modified in a way that removed its mapping from the cell database.

Without this mapping, Nova is unable to schedule workloads on the host, even if it appears active and functional.

Diagnostics

1. Run the following command from the nova-scheduler pod on Management Plane to see if the host is linked to a cell:

$ nova-manage cell_v2 list_hosts
+--------------+--------------+---------------------+
|  Cell Name   |   Cell UUID  |       Hostname      |
+--------------+--------------+---------------------+
| [CELL_NAME]  | [CELL_UUID]  | [HOST1.EXAMPLE.COM] |
| [CELL_NAME]  | [CELL_UUID]  | [HOST2.EXAMPLE.COM] |
+--------------+--------------+---------------------+

1. The compute service on the host still might be visible and enabled:

$ openstack compute service list --host <HOST3.EXAMPLE.COM>
+------------------------+--------------+---------------------+-----------------+---------+-------+--------------+
| ID                     | Binary       | Host                | Zone            | Status  | State | Updated At   |
+------------------------+--------------+---------------------+---------------------------+-------+--------------+
| [COMPUTE_SERVICE_UUID] | nova-compute | [HOST3.EXAMPLE.COM] | [CLUSTER_NAME]  | enabled | up    | [TIME_STAMP] |
+------------------------+--------------+--------------+------------------------+---------+-------+--------------+

Resolution

1. Run the following command from nova-scheduler pod on Management Plane to find any unmapped compute hosts and create their cell mappings:

$ nova-manage cell_v2 discover_hosts --verbose --by-service

Found [CELL_MAPPINGS_COUNT] cell mappings.
Getting computes from cell '[CELL_NAME]': [CELL_UUID]
Creating host mapping for service [HOST3.EXAMPLE.COM]
Found [MISSING_COMPUTES_COUNT] unmapped computes in cell: [CELL_UUID]

Validation

1. Confirm the host is mapped to a cell.

$ nova-manage cell_v2 list_hosts
+--------------+-------------+---------------------+
|  Cell Name   |  Cell UUID  |      Hostname       |
+--------------+-------------+---------------------+
| [CELL_NAME]  | [CELL_UUID] | [HOST1.EXAMPLE.COM] |
| [CELL_NAME]  | [CELL_UUID] | [HOST2.EXAMPLE.COM] |
| [CELL_NAME]  | [CELL_UUID] | [HOST3.EXAMPLE.COM] |
+--------------+-------------+---------------------+

1. Verify the compute service is active

$ openstack compute service list --host <HOST3.EXAMPLE.COM>
+------------------------+--------------+---------------------+-----------------+---------+-------+--------------+
| ID                     | Binary       | Host                | Zone            | Status  | State | Updated At   |
+------------------------+--------------+---------------------+---------------------------+-------+--------------+
| [COMPUTE_SERVICE_UUID] | nova-compute | [HOST3.EXAMPLE.COM] | [CLUSTER_NAME]  | enabled | up    | [TIME_STAMP] |
+------------------------+--------------+--------------+------------------------+---------+-------+--------------+

1. Attempt to launch a virtual machine and confirm it succeeds.