# Ironic

## Introduction

The ironic hypervisor driver wraps the Bare Metal (ironic) API, enabling Nova to provision baremetal resources using the same user-facing API as for server management.

This is the only driver in nova where one compute service can map to many hosts, meaning a `nova-compute` service can manage multiple `ComputeNodes`. An ironic driver managed compute service uses the ironic `node uuid` for the compute node `hypervisor_hostname` (nodename) and `uuid` fields. The relationship of `instance:compute node:ironic node` is 1:1:1.

Scheduling of bare metal nodes is based on custom resource classes, specified via the `resource_class` property on a node and a corresponding resource property on a flavor (see the flavor documentation). The RAM and CPU settings on a flavor are ignored, and the disk is only used to determine the root partition size when a partition image is used (see the image documentation).

## VNC console support

The nova noVNC VNC console service can connect to bare metal nodes when ironic has Graphical console support enabled and configured.

## Configuration

- Configure the Compute service to use the Bare Metal service.

- Create flavors for use with the Bare Metal service.

- Conductors Groups.

## Scaling and performance issues

- It is typical for a single nova-compute process to support several hundred Ironic nodes. There are known issues when you attempt to support more than 1000 Ironic nodes associated with a single nova-compute process, even though Ironic is able to scale out a single conductor group to much larger sizes. There are many other factors that can affect what is the maximum practical size of a conductor group within your deployment.

- The `update_available_resource` periodic task reports all the resources managed by Ironic. Depending the number of nodes, it can take a lot of time. The nova-compute will not perform any other operations when this task is running. You can use conductor groups to help shard your deployment between multiple nova-compute processes by setting `ironic.conductor_group`.

- The nova-compute process using the Ironic driver can be moved between different physical servers using active/passive failover. But when doing this failover, you must ensure `host` is the same no matter where the nova-compute process is running. Similarly you must ensure there are at most one nova-compute processes running for each conductor group.

- Running multiple nova-compute processes that point at the same conductor group is now deprecated. Please never have more than one host in the peer list: `ironic.peer_list`

## Known limitations / Missing features

- Migrate

- Resize

- Snapshot

- Pause

- Shelve

- Evacuate

this page last updated: 2026-06-08 08:40:45

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