# VM Build Failure Due to Nova Timeout

## Problem

The VM build is failing, and the following errors are seen in `ostackhost log`:

<pre data-overflow="wrap"><code><strong>INFO nova.compute.resource_tracker [[REQ_UUID] None None] Instance [VM_UUID] has allocations against this compute host but is not found in the database.
</strong>ERROR nova.compute.manager [[REQ_UUID] None None] Error updating resources for node [HOSTNAME]: oslo_messaging.exceptions.MessagingTimeout: Timed out waiting for a reply to message ID [MSG_UUID] 
</code></pre>

## Environment

* Self-Hosted Private Cloud Director Virtualization - v2025.10 and Higher
* Component: Compute Service

## Cause

The root cause is the RPC response timeout threshold being exceeded for communication between **Nova Compute** and **Nova Conductor** via **RabbitMQ**.

> Optimizing the timeout value based on environmental factors can improve performance. In scenarios with slower networks or other delays, adjusting the Nova configuration helps ensure efficient request processing.

## Workaround

Increase the following parameters in the Nova configuration to allow more time for RPC communication and service reporting:

| Parameter              | Default Value | Updated Value |
| ---------------------- | ------------- | ------------- |
| `rpc_response_timeout` | 120s          | **180s**      |
| `report_interval`      | 60s           | **120s**      |

**1. On the Management Cluster (Control Plane)**

* Update the `nova-etc` Kubernetes secret with the new values.
* Restart the `nova-api-osapi` pods to pick up the changes.
* Verify the updated values are reflected in:

  ```bash
  /etc/pf9/nova/conf.d/nova.conf
  ```

**2. On Each Compute Host**

* Update the following file with the new parameter values:

  ```bash
  /opt/pf9/etc/nova/conf.d/nova.conf
  ```

  Add or modify under the `[DEFAULT]` section:

  ```ini
  [DEFAULT]
  rpc_response_timeout = 180
  report_interval = 120
  ```
* Restart the `pf9-ostackhost` service:

  ```bash
  sudo systemctl restart pf9-ostackhost
  ```

> **Note:** This change must be applied on **all compute hosts**.&#x20;

## Validation

After applying the changes to both the control plane and all compute hosts:

1. Attempt to provision multiple VMs concurrently (burst provisioning).
2. Monitor the `ostackhost.log` on the compute hosts for any recurrence of `MessagingTimeout` errors.
3. Check RabbitMQ pod logs for a reduction in `missed heartbeats from client` errors.
4. Confirm VMs are successfully built without entering ERROR or stuck BUILD state.


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