ironic-python-agent/doc/source/contributor/hardware_managers.rst

Hardware Managers

Hardware managers are how IPA supports multiple different hardware platforms in the same agent. Any action performed on hardware can be overridden by deploying your own hardware manager.

IPA ships with GenericHardwareManager </admin/hardware_managers>, which implements basic cleaning and deployment methods compatible with most hardware.

Warning

Some functionality inherent in the stock hardware manager cleaning methods may be useful in custom hardware managers, but should not be inherently expected to also work in custom managers. Examples of this are clustered filesystem protections, and cleaning method fallback logic. Custom hardware manager maintainers should be mindful when overriding the stock methods.

How are methods executed on HardwareManagers?

Methods that modify hardware are dispatched to each hardware manager in priority order. When a method is dispatched, if a hardware manager does not have a method by that name or raises IncompatibleHardwareMethodError, IPA continues on to the next hardware manager. Any hardware manager that returns a result from the method call is considered a success and its return value passed on to whatever dispatched the method. If the method is unable to run successfully on any hardware managers, HardwareManagerMethodNotFound is raised.

Why build a custom HardwareManager?

Custom hardware managers allow you to include hardware-specific tools, files and cleaning steps in the Ironic Python Agent. For example, you could include a BIOS flashing utility and BIOS file in a custom ramdisk. Your custom hardware manager could expose a cleaning step that calls the flashing utility and flashes the packaged BIOS version (or even download it from a tested web server).

How can I build a custom HardwareManager?

In general, custom HardwareManagers should subclass hardware.HardwareManager. Subclassing hardware.GenericHardwareManager should only be considered if the aim is to raise the priority of all methods of the GenericHardwareManager. The only required method is evaluate_hardware_support(), which should return one of the enums in hardware.HardwareSupport. Hardware support determines which hardware manager is executed first for a given function (see: "How are methods executed on HardwareManagers?" for more info). Common methods you may want to implement are list_hardware_info(), to add additional hardware the GenericHardwareManager is unable to identify and erase_devices(), to erase devices in ways other than ATA secure erase or shredding.

Some reusable functions are provided by ironic-lib <reference/api/modules.html>, its IPA is relatively stable.

The examples directory has two example hardware managers that can be copied and adapter for your use case.

Custom HardwareManagers and Cleaning

One of the reasons to build a custom hardware manager is to expose extra steps in Ironic Cleaning </admin/cleaning.html>. A node will perform a set of cleaning steps any time the node is deleted by a tenant or moved from manageable state to available state. Ironic will query IPA for a list of clean steps that should be executed on the node. IPA will dispatch a call to get_clean_steps() on all available hardware managers and then return the combined list to Ironic.

To expose extra clean steps, the custom hardware manager should have a function named get_clean_steps() which returns a list of dictionaries. The dictionaries should be in the form:

def get_clean_steps(self, node, ports):
    return [
        {
            # A function on the custom hardware manager
            'step': 'upgrade_firmware',
            # An integer priority. Largest priorities are executed first
            'priority': 10,
            # Should always be the deploy interface
            'interface': 'deploy',
            # Request the node to be rebooted out of band by Ironic when
            # the step completes successfully
            'reboot_requested': False
        }
    ]

Then, you should create functions which match each of the step keys in the clean steps you return. The functions will take two parameters: node, a dictionary representation of the Ironic node, and ports, a list of dictionary representations of the Ironic ports attached to node.

When a clean step is executed in IPA, the step key will be sent to the hardware managers in hardware support order, using hardware.dispatch_to_managers(). For each hardware manager, if the manager has a function matching the step key, it will be executed. If the function returns a value (including None), that value is returned to Ironic and no further managers are called. If the function raises IncompatibleHardwareMethodError, the next manager will be called. If the function raises any other exception, the command will be considered failed, the command result's error message will be set to the exception's error message, and no further managers will be called. An example step:

def upgrade_firmware(self, node, ports):
    if self._device_exists():
        # Do the upgrade
        return 'upgraded firmware'
    else:
        raise errors.IncompatibleHardwareMethodError()

If the step has args, you need to add them to argsinfo and provide the function with extra parameters.

def get_clean_steps(self, node, ports):
    return [
        {
            # A function on the custom hardware manager
            'step': 'upgrade_firmware',
            # An integer priority. Largest priorities are executed first
            'priority': 10,
            # Should always be the deploy interface
            'interface': 'deploy',
            # Arguments that can be required or optional.
            'argsinfo': {
                'firmware_url': {
                    'description': 'Url for firmware',
                    'required': True,
                },
            }
            # Request the node to be rebooted out of band by Ironic when
            # the step completes successfully
            'reboot_requested': False
        }
    ]

def upgrade_firmware(self, node, ports, firmware_url):
    if self._device_exists():
        # Do the upgrade
        return 'upgraded firmware'
    else:
        raise errors.IncompatibleHardwareMethodError()

Note

If two managers return steps with the same step key, the priority will be set to whichever manager has a higher hardware support level and then use the higher priority in the case of a tie.

In some cases, it may be necessary to create a customized cleaning step to take a particular pattern of behavior. Those doing such work may want to leverage file system safety checks, which are part of the stock hardware managers.

def custom_erase_devices(self, node, ports):
    for dev in determine_my_devices_to_erase():
        hardware.safety_check_block_device(node, dev.name)
        my_special_cleaning(dev.name)

Custom HardwareManagers and Deploying

Starting with the Victoria release cycle, deployment <admin/node-deployment.html> can be customized similarly to cleaning. A hardware manager can define deploy steps that may be run during deployment by exposing a get_deploy_steps call.

There are two kinds of deploy steps:

1. Steps that need to be run automatically must have a non-zero priority and cannot take required arguments. For example:

   def get_deploy_steps(self, node, ports):
       return [
           {
               # A function on the custom hardware manager
               'step': 'upgrade_firmware',
               # An integer priority. Largest priorities are executed first
               'priority': 10,
               # Should always be the deploy interface
               'interface': 'deploy',
           }
       ]
   
   # A deploy steps looks the same as a clean step.
   def upgrade_firmware(self, node, ports):
       if self._device_exists():
           # Do the upgrade
           return 'upgraded firmware'
       else:
           raise errors.IncompatibleHardwareMethodError()

   Priority should be picked based on when exactly in the process the step will run. See agent step priorities <admin/node-deployment.html#agent-steps> for guidance.

2. Steps that will be requested via deploy templates <admin/node-deployment.html#deploy-templates> should have a priority of 0 and may take both required and optional arguments that will be provided via the deploy templates. For example:

   def get_deploy_steps(self, node, ports):
       return [
           {
               # A function on the custom hardware manager
               'step': 'write_a_file',
               # Steps with priority 0 don't run by default.
               'priority': 0,
               # Should be the deploy interface, unless there is driver-side
               # support for another interface (as it is for RAID).
               'interface': 'deploy',
               # Arguments that can be required or optional.
               'argsinfo': {
                   'path': {
                       'description': 'Path to file',
                       'required': True,
                   },
                   'content': {
                       'description': 'Content of the file',
                       'required': True,
                   },
                   'mode': {
                       'description': 'Mode of the file, defaults to 0644',
                       'required': False,
                   },
               }
           }
       ]
   
   def write_a_file(self, node, ports, path, contents, mode=0o644):
       pass  # Mount the disk, write a file.

Versioning

Each hardware manager has a name and a version. This version is used during cleaning to ensure the same version of the agent is used to on a node through the entire process. If the version changes, cleaning is restarted from the beginning to ensure consistent cleaning operations and to make updating the agent in production simpler.

You can set the version of your hardware manager by creating a class variable named 'HARDWARE_MANAGER_VERSION', which should be a string. The default value is '1.0'. You should change this version string any time you update your hardware manager. You can also change the name your hardware manager presents by creating a class variable called HARDWARE_MANAGER_NAME, which is a string. The name defaults to the class name. Currently IPA only compares version as a string; any version change whatsoever will induce cleaning to restart.

Priority

A hardware manager has a single overall priority, which should be based on how well it supports a given piece of hardware. At load time, IPA executes evaluate_hardware_support() on each hardware manager. This method should return an int representing hardware manager priority, based on what it detects about the platform it's running on. Suggested values are included in the HardwareSupport class. Returning a value of 0 aka HardwareSupport.NONE, will prevent the hardware manager from being used. IPA will never ship a hardware manager with a priority higher than 3, aka HardwareSupport.SERVICE_PROVIDER.