Metal to Tenant: Ironic in Overcloud

This blueprint adds support for providing bare metal machines to tenants by integrating Ironic to the overcloud.

Problem Description

There is an increasing interest in providing bare metal machines to tenants in the overcloud in addition to or instead of virtual instances. One example is Sahara: users hope to achieve better performance by removing the hypervisor abstraction layer in order to eliminate the noisy neighbor effect. For that purpose, the OpenStack Bare metal service (Ironic) provides an API and a Nova driver to serve bare metal instances behind the same Nova and Neutron API’s. Currently however TripleO does not support installing and configuring Ironic and Nova to serve bare metal instances to the tenant.

Proposed Change

Composable Services

In the bare metal deployment case, the nova-compute service is only a thin abstraction layer around the Ironic API. The actual compute instances in this case are the bare metal nodes. Thus a TripleO deployment with support for only bare metal nodes will not need dedicated compute nodes in the overcloud. The overcloud nova-compute service will therefore be placed on controller nodes.

New TripleO composable services will be created and optionally deployed on the controller nodes:

  • OS::TripleO::Services::IronicApi will deploy the bare metal API.

  • OS::TripleO::Services::IronicNovaCompute will deploy nova compute with Ironic as a back end. It will also configure the nova compute to use ClusteredComputeManager provide by Ironic to work around inability to have several nova compute instances configured with Ironic.

  • OS::TripleO::Services::IronicConductor will deploy a TFTP server, an HTTP server (for an optional iPXE environment) and an ironic-conductor instance. The ironic-conductor instance will not be managed by pacemaker in the HA scenario, as Ironic has its own Active/Active HA model, which spreads load on all active conductors using a hash ring.

    There is no public data on how many bare metal nodes each conductor can handle, but the Ironic team expects an order of hundreds of nodes per conductor.

Since this feature is not a requirement in all deployments, this will be opt-in by having a separate environment file.

Hybrid Deployments

For hybrid deployments with both virtual and bare metal instances, we will use Nova host aggregates: one for all bare metal hosts, the other for all virtual compute nodes. This will prevent virtual instances being deployed on baremetal nodes. Note that every bare metal machine is presented as a separate Nova compute host. These host aggregates will always be created, even for purely bare metal deployments, as users might want to add virtual computes later.


As of Mitaka, Ironic only supports flat networking for all tenants and for provisioning. The recommended deployment layout will consist of two networks:

  • The provisioning / tenant network. It must have access to the overcloud Neutron service for DHCP, and to overcloud baremetal-conductors for provisioning.


    While this network can technically be the same as the undercloud provisioning network, it’s not recommended to do so due to potential conflicts between various DHCP servers provided by Neutron (and in the future by ironic-inspector).

  • The management network. It will contain the BMCs of bare metal nodes, and it only needs access to baremetal-conductors. No tenant access will be provided to this network.


    Splitting away this network is not really required if tenants are trusted (which is assumed in this spec) and BMC access is reasonably restricted.


To limit the scope of this spec the following definitely useful features are explicitly left out for now:

  • provision <-> tenant network separation (not yet implemented by ironic)

  • in-band inspection (requires ironic-inspector, which is not yet HA-ready)

  • untrusted tenants (requires configuring secure boot and checking firmwares, which is vendor-dependent)

  • node autodiscovery (depends on ironic-inspector)


Alternatively, we could leave configuring a metal-to-tenant environment up to the operator.

We could also have it enabled by default, but most likely it won’t be required in most deployments.

Security Impact

Most of the security implications have to be handled within Ironic. Eg. wiping the hard disk, checking firmwares, etc. Ironic needs to be configured to be able to run these jobs by enabling automatic cleaning during node lifecycle. It is also worth mentioning that we will assume trusted tenants for these bare metal machines.

Other End User Impact

The ability to deploy Ironic in the overcloud will be optional.

Performance Impact

If enabled, TripleO will deploy additional services to the overcloud:

  • ironic-conductor

  • a TFTP server

  • an HTTP server

None of these should have heavy performance requirements.

Other Deployer Impact


Developer Impact




Primary assignee:


Other contributors:

dtantsur, lucasagomes, mgould, mkovacik

Work Items

when the environment file is included, make sure:

  • ironic is deployed on baremetal-conductor nodes

  • nova compute is deployed and correctly configured, including:

    • configuring Ironic as a virt driver

    • configuring ClusteredComputeManager

    • setting ram_allocation_ratio to 1.0

  • host aggregates are created

  • update documentation




This is testable in the CI with nested virtualization and tests will be added to the tripleo-ci jobs.

Documentation Impact

  • Quick start documentation and a sample environment file will be provided.

  • Document how to enroll new nodes in overcloud ironic (including host aggregates)