# Compute Service Customization

The `nova_override.conf` file is a custom configuration file used in Platform9's <code class="expression">space.vars.product\_name</code> to allow you to override default configurations for <code class="expression">space.vars.product\_name</code> compute service. These overrides persist across upgrades, ensuring that your customized settings remain intact.

Note that updating nova\_override.conf file is an **advance operation and should only be performed by Administrators** with complete understanding of the option they are editing and the possible impact. We highly recommend that you do this only under guidance from Platform9 support or solution architect teams.

{% hint style="danger" %}
**Important**

Updating nova\_override.conf file is an advance operation and must only be performed by Administrators with complete understanding of the option being edited and side effects / impact if any. We highly recommend doing this only under guidance from Platform9 support team or solution architect team.
{% endhint %}

The `nova_override.conf` file is typically located in the following directory.

{% tabs %}
{% tab title="Bash" %}

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

{% endtab %}
{% endtabs %}

{% hint style="info" %}
**Info**

The `nova_override` file must be edited on **each hypervisor host** where the override configurations are required. This ensures that the custom settings apply consistently across all compute nodes.
{% endhint %}

You can use this override file to:

* Adjust logging levels or enabling more verbose logging by enabling debug mode. (Mostly commonly used case).
* Customize compute driver options.
* Modify quota defaults for specific tenants.

Here is an example of a `nova_override.conf` file customized for common use cases like for logging, debugging, and optimization.. For more info, refer to [nova.conf](https://docs.openstack.org/ocata/config-reference/compute/config-options.html).

### Logging & Debugging

Safe for troubleshooting but should be reverted in production.

{% tabs %}
{% tab title="Bash" %}

```bash
[DEFAULT]
debug = true  # Enable detailed logging (useful for troubleshooting)
log_dir = /var/log/nova  # Log file storage location
```

{% endtab %}
{% endtabs %}

### Scheduler Configuration

Can be adjusted to improve VM scheduling behavior.

{% tabs %}
{% tab title="Bash" %}

```bash
[scheduler]
max_attempts = 5  # Number of retries for scheduling instances
```

{% endtab %}
{% endtabs %}

### Compute Resource Limits

Can be modified based on hardware capacity.

{% tabs %}
{% tab title="Bash" %}

```bash
[DEFAULT]
reserved_host_memory_mb = 2048  # Reserve memory for the hypervisor
cpu_allocation_ratio = 16.0  # Overcommit CPU resources (Default: 16)
ram_allocation_ratio = 1.5  # Overcommit RAM resources (Default: 1.5)
```

{% endtab %}
{% endtabs %}

## Restart Service

After editing the `nova_override.conf` file, you must restart the <code class="expression">space.vars.product\_name</code> compute service for the changes to take effect. Run the following command on the host:

{% tabs %}
{% tab title="Bash" %}

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

{% endtab %}
{% endtabs %}

## Advance Settings

{% hint style="warning" %}
**Warning**

These settings impact VM operations and performance. Modify only if necessary and test changes in a non-production environment.
{% endhint %}

### Compute Driver Configuration

{% tabs %}
{% tab title="Bash" %}

```bash
[DEFAULT]
compute_driver = nova.virt.libvirt.LibvirtDriver
```

{% endtab %}
{% endtabs %}

Do not change unless you are configuring a different virtualization technology (e.g., VMware, Xen, KVM).

### Networking Configuration

{% tabs %}
{% tab title="Bash" %}

```bash
[neutron]
service_plugins = router,metering
```

{% endtab %}
{% endtabs %}

Changing networking parameters without proper testing may break VM connectivity.

### Disk & Storage Settings

{% tabs %}
{% tab title="Bash" %}

```bash
[libvirt]
images_type = qcow2  # Default disk image format
live_migration_flag = VIR_MIGRATE_LIVE
```

{% endtab %}
{% endtabs %}

Modify only if you are implementing specific storage optimizations.

### CPU Mode and Model Configuration

{% tabs %}
{% tab title="Bash" %}

```bash
[libvirt]
# Specifies the CPU mode for virtual machine instances.
cpu_mode = custom
# Defines the custom CPU model(s) to be used with the hypervisor.
cpu_models = Broadwell-noTSX-IBRS
```

{% endtab %}
{% endtabs %}

This configuration is typically used when you need consistent CPU features across different hypervisors.


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