> For the complete documentation index, see [llms.txt](https://platform9.com/kb/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://platform9.com/kb/pcd/compute/vm-fails-to-start-after-flavor-resize.md).

# VM Fails to Start After Flavor Resize

## Problem

After successfully resizing the flavor of the VM, it is unable to start.

## Environment

* Private Cloud Director Virtualization - v2025.4 and Higher
* Self-Hosted Private Cloud Director Virtualization - v2025.4 and Higher
* Component: Compute Service

## Cause

There is a transient desynchronization between the Compute service and the hypervisor, where the instance state in the database did not match the actual state on the compute node.

## Diagnostics

1. Verify if the reported VM is present in the libvirt database on the compute host. 

{% code title="Host" overflow="wrap" %}

```bash
$ sudo virsh list --all | grep <VM_UUID>
```

{% endcode %}

2. Review the `/var/log/pf9/ostackhost.logs` over the compute host for the impacted VM. It complains around the soft reboot of the VM after successful flavor resize, has not completely deleted the older allocations \[from the old flavor].

{% code title="/var/log/pf9/ostackhost.logs" overflow="wrap" %}

```bash
INFO nova.compute.manager [[REQUEST_ID] [USER_NAME] service] [instance: [INSTANCE_ID]] Deleting allocations for old flavor on source node [COMPUTE_ID] after finish_resize failure. You may be able to recover the instance by hard rebooting it. 
```

{% endcode %}

3. The `ostackhost.log` also points to a mismatch in the instance count and intermittent "*Instance not found*” messages.

{% code title="/var/log/pf9/ostackhost.logs" overflow="wrap" %}

```bash
WARNING nova.compute.manager: While synchronizing instance power states, found 3 instances in the database and 2 instances on the hypervisor.
WARNING nova.compute.manager [instance: [INSTANCE_ID]]: Instance is unexpectedly not found. Ignore.
```

{% endcode %}

## Resolution

* Perform a [**HARD REBOOT**](https://docs.platform9.com/private-cloud-director/virtualized-clusters/virtualmachine/virtual-machine-actions#hard-reboot) of the affected VM to force a resynchronization between Nova and the hypervisor, which will bring the VM back to a healthy state.

## Validation

* Confirm the VM is now in **ACTIVE** state:

```bash
$ openstack server show -c status <VM_ID> 
```

* Ensure it is hosted correctly:

```bash
$ openstack server show -c OS-EXT-SRV-ATTR:hypervisor_hostname <VM_UUID>
```

* Ensure the VM is present in the active libvirt domains on the hypervisor.

{% code title="Host" overflow="wrap" %}

```bash
$ sudo virsh list --all | grep <VM_UUID>
```

{% endcode %}


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