Pluggable Drivers

Ironic supports a pluggable driver model. This allows contributors to easily add new drivers, and operators to use third-party drivers or write their own. A driver is built at runtime from a hardware type and hardware interfaces. See Enabling drivers and hardware types for a detailed explanation of these concepts.

Hardware types and interfaces are loaded by the ironic-conductor service during initialization from the setuptools entrypoints ironic.hardware.types and ironic.hardware.interfaces.<INTERFACE> where <INTERFACE> is an interface type (for example, deploy). Only hardware types listed in the configuration option enabled_hardware_types and interfaces listed in configuration options enabled_<INTERFACE>_interfaces are loaded. A complete list of hardware types available on the system may be found by enumerating this entrypoint by running the following python script:

#!/usr/bin/env python

import pkg_resources as pkg
print [p.name for p in pkg.iter_entry_points("ironic.hardware.types") if not p.name.startswith("fake")]

A list of drivers enabled in a running Ironic service may be found by issuing the following command against that API end point:

baremetal driver list

Writing a hardware type

A hardware type is a Python class, inheriting ironic.drivers.hardware_type.AbstractHardwareType and listed in the setuptools entry point ironic.hardware.types. Most of the real world hardware types inherit ironic.drivers.generic.GenericHardware instead. This helper class provides useful implementations for interfaces that are usually the same for all hardware types, such as deploy.

The minimum required interfaces are:

  • boot that specifies how to boot ramdisks and instances on the hardware. A generic pxe implementation is provided by the GenericHardware base class.

  • deploy that orchestrates the deployment. A few common implementations are provided by the GenericHardware base class.

    As of the Rocky release, a deploy interface should decorate its deploy method to indicate that it is a deploy step. Conventionally, the deploy method uses a priority of 100.

    @ironic.drivers.base.deploy_step(priority=100)
def deploy(self, task):

    Note

    Most of the hardware types should not override this interface.

  • power implements power actions for the hardware. These common implementations may be used, if supported by the hardware:

    Otherwise, you need to write your own implementation by subclassing ironic.drivers.base.PowerInterface and providing missing methods.

    Note

    Power actions in Ironic are blocking - methods of a power interface should not return until the power action is finished or errors out.

  • management implements additional out-of-band management actions, such as setting a boot device. A few common implementations exist and may be used, if supported by the hardware:

    Some hardware types, such as snmp do not support out-of-band management. They use the fake implementation in ironic.drivers.modules.fake.FakeManagement instead.

    Otherwise, you need to write your own implementation by subclassing ironic.drivers.base.ManagementInterface and providing missing methods.

Combine the interfaces in a hardware type by populating the lists of supported interfaces. These lists are prioritized, with the most preferred implementation first. For example:

class MyHardware(generic.GenericHardware):

    @property
    def supported_management_interfaces(self):
        """List of supported management interfaces."""
        return [MyManagement, ipmitool.IPMIManagement]

    @property
    def supported_power_interfaces(self):
        """List of supported power interfaces."""
        return [MyPower, ipmitool.IPMIPower]

Note

In this example, all interfaces, except for management and power are taken from the GenericHardware base class.

Finally, give the new hardware type and new interfaces human-friendly names and create entry points for them in the setup.cfg file:

ironic.hardware.types =
    my-hardware = ironic.drivers.my_hardware:MyHardware
ironic.hardware.interfaces.power =
    my-power = ironic.drivers.modules.my_hardware:MyPower
ironic.hardware.interfaces.management =
    my-management = ironic.drivers.modules.my_hardware:MyManagement

Deploy and clean steps

Significant parts of the bare metal functionality is implemented via deploy steps or clean steps. See Developing deploy and clean steps for information on how to write them.

Supported Drivers

For a list of supported drivers (those that are continuously tested on every upstream commit) please consult the drivers page.