Compute Driver Interface

https://blueprints.launchpad.net/octavia/+spec/compute-driver-interface

This blueprint describes how a driver will interface with Nova to manage the creation and deletion of amphora instances. It will describe the base class and other classes required to create, delete, manage the execution state, and query the status of amphorae.

Problem description

The controller needs to be able to create, delete, and monitor the status of amphora instances. The amphorae may be virtual machines, containers, bare-metal servers, or dedicated hardware load balancers. This interface should hide the implementation details of the amphorae from the caller to the maximum extent possible.

This interface will provide means to specify:
  • type (VM, Container, bare metal)
  • flavor (provides means to specify memory and storage capacity)
  • what else?

Proposed change

Establish an abstract base class to model the desired functionality:

class AmphoraComputeDriver(object):

    def build(self, amphora_type = VM, amphora_flavor = None,
              image_id = None, keys = None, sec_groups = None,
              network_ids = None,config_drive_files = None,user_data=None):

        """ build a new amphora.

        :param amphora_type: The type of amphora to create.  For
        version 0.5, only VM is supported.  In the future this
        may support Container, BareMetal, and HWLoadBalancer.
        :param amphora_flavor: Optionally specify a flavor.  The
        interpretation of this parameter will depend upon the
        amphora type and may not be applicable to all types.
        :param image_id: ID of the base image for a VM amphora
        :param keys: Optionally specify a list of ssh public keys
        :param sec_groups: Optionally specify list of security
        groups
        :param network_ids: A list of network_ids to attach to
        the amphora
        :config_drive_files:  A dict of files to overrwrite on
        the server upon boot. Keys are file names (i.e. /etc/passwd)
        and values are the file contents (either as a string or as
        a file-like object). A maximum of five entries is allowed,
        and each file must be 10k or less.
        :param user_data: user data to pass to be exposed by the
        metadata server this can be a file type object as well or
        a string

        :returns: The id of the new instance.

        """

        raise NotImplementedError

    def delete(self, amphora_id):
        """  delete the specified amphora
        """

        raise NotImplementedError

    def status(self, amphora_id):

        """ Check whether the specified amphora is up

        :param amphora_id: the ID of the desired amphora
        :returns: the nova response from the amphora
        """
        raise NotImplementedError

    def get_amphora(self, amphora_name = None, amphora_id = None):
        """ Try to find an amphora given its name or id

        :param amphora_name: the name of the desired amphora
        :param amphora_id: the id of the desired amphora
        :returns: the amphora object
        """
        raise NotImplementedError

Exception Model

The driver is expected to raise the following well defined exceptions:

  • NotImplementedError - this functionality is not implemented/not supported
  • AmphoraComputeError - a super class for all other exceptions and the catch
    all if no specific exception can be found
    • AmphoraBuildError - An amphora of the specified type could not be built
    • DeleteFailed - this amphora couldn’t be deleted
  • InstanceNotFoundError - an instance matching the desired criteria could not be found
  • NotSuspendedError - resume() attempted on an instance that was not suspended

Things a good driver should do:

  • Non blocking operations - If an operation will take a long time to execute, perform it asynchronously. The definition of “a long time” is open to interpretation, but a common UX guideline is 200 ms
  • We might employ a circuit breaker to insulate driver problems from controller problems [1]
  • Use appropriate logging
  • Use the preferred threading model

This will be demonstrated in the Noop-driver code.

Alternatives

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None - since initial version

Other end user impact

None

Performance Impact

Minimal

Other deployer impact

Deployers need to make sure to bundle the compatible versions of amphora, driver, controller –

Developer impact

Need to write towards this clean interface.

Implementation

Assignee(s)

Al Miller

Work Items

  • Write abstract interface
  • Write Noop driver
  • Write tests

Dependencies

None

Testing

  • Unit tests with tox and Noop-Driver
  • tempest tests with Noop-Driver

Documentation Impact

None - this is an internal interface and need not be externally documented.