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

## Problem

Virtual Machine creation fails with the following error:

```bash
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](https://support.platform9.com/hc/en-us).

## 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:

```bash
$ 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] |
+--------------+--------------+---------------------+
```

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

```bash
$ 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:

```bash
$ 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.

```bash
$ 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] |
+--------------+-------------+---------------------+
```

2. Verify the compute service is active

```bash
$ 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] |
+------------------------+--------------+--------------+------------------------+---------+-------+--------------+
```

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


---

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