Determinable supported boot device list

https://blueprints.launchpad.net/ironic/+spec/supported-boot-device-list

This blueprint proposes to add the facility to return a determinable list of supported boot devices that is specific to the node being queried.

Problem description

Current driver interface get_supported_boot_devices() does not provide for a means to access the node being queried, as a result a determinable list of supported boot devices that are specific to this node cannot be calculated.

Example usage, if a node uses an architecture other than x86 e.g. SPARC, then PXE boot is not supported, and therefore should not be contained in the returned list. SPARC architecture supports WANBOOT and this should be returned. However to determine this the node’s property “cpu_arch” needs to be accessed.

Proposed change

Add “task” parameter to get_supported_boot_devices() interface.

By providing a task parameter to the get_supported_boot_devices() interface a driver can then access the node specific to this query e.g. task.node, and from there can look at a nodes properties and correctly determine the list of supported boot devices to return.

This change would be backwards compatible, using inspect to determine if a specific driver as implemented the “task” parameter or not, and showing a deprecation warning if “task” paramater has not been implemented.

This deprecation of get_suported_boot_devices() without task parameter will be done in the next release, after which get_supported_boot_devices() without the task parameter will not be supported.

Alternatives

The only method to access the specific node for which a get_supported_boot_devices request is being made is via passing in the task argument.

Alternative 1: Restrict all drivers to only be able to register nodes of a specific architecture. Then the underlying driver API for get_supported_boot_devices() would just assume that this node must be of a specific architecture and always return a static list for that architecture.

This approach is limiting and would result in an unnecessary increase in the number of drivers available for ironic, and a unnecessary potential duplication of code.

Alternative 2: Utilize set_boot_device(task, device), this method in most cases will validate if a “device” is supported for this node. A task parameter is being passed in here, and thus the node can be accessed to determine if “device” is supported for this specific node. The issue here is that it would have to be called a number of times to determine a list of supported devices, and each successful call would result in an IPMI call to actually set the boot device for the node which would be unacceptable and inefficient.

This approach is not complete and does not solve the scenario where get_supported_boot_devices() is called via the ironic CLI. This would still result in a potentially incorrect list of devices being returned to the user.

Alternative 3: This is more of an addendum to the proposed solution. Add a new essential property for a node called “supported_boot_devices”. This property would be populated during node inspection, and could then be queried to determine the list of supported boot devices.

Access to the node however would still be required, so passing of the task parameter to get_supported_boot_devices would still be required.

Data model impact

None

State Machine Impact

None

REST API impact

None

Client (CLI) impact

None

RPC API impact

None

Driver API impact

get_supported_device_list() is a member of the standard Management interface.

This change would effect all drivers but would be implemented so that it’s backward compatible, using inspect to determine if a driver supports the task argument or not. If not a deprecation warning would be shown.

Nova driver impact

None

Security impact

None

Other end user impact

None

Scalability impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

All in-tree driver and unit tests will be amended to include the new “task” parameter. Out of tree drivers will see a depracation warning until they implement the new “task” parameter.

Implementation

Assignee(s)

Primary assignee:
mattkeenan

Work Items

  • Add “task” to get_supported_devices_list() in base driver
  • Add new management property definition to check if driver supports task parameter or not.
  • Update all in tree drivers adding task paramater
  • Update all unit tests affected by change

Dependencies

None

Testing

Will update all affected unit tests

Upgrades and Backwards Compatibility

Backwards compatibility is achieved by using python’s inspect module to determine if a driver’s get_supported_device_list() implementation includes a “task” parameter or not. If not it will be called without the “task” parameter and a deprecation warning will be shown.

Documentation Impact

None