OpenStack Study: manager.py

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# Copyright 2010 United States Government as represented by the

# Administrator of the National Aeronautics and Space Administration.

# All Rights Reserved.


# Licensed under the Apache License, Version 2.0 (the "License"); you may

# not use this file except in compliance with the License. You may obtain

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# http://www.apache.org/licenses/LICENSE-2.0


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"""Base Manager class.

Managers are responsible for a certain aspect of the system. It is a logical

grouping of code relating to a portion of the system. In general other

components should be using the manager to make changes to the components that

it is responsible for.

For example, other components that need to deal with volumes in some way,

should do so by calling methods on the VolumeManager instead of directly

changing fields in the database. This allows us to keep all of the code

relating to volumes in the same place.

We have adopted a basic strategy of Smart managers and dumb data, which means

rather than attaching methods to data objects, components should call manager

methods that act on the data.

Methods on managers that can be executed locally should be called directly. If

a particular method must execute on a remote host, this should be done via rpc

to the service that wraps the manager

Managers should be responsible for most of the db access, and

non-implementation specific data. Anything implementation specific that can't

be generalized should be done by the Driver.

In general, we prefer to have one manager with multiple drivers for different

implementations, but sometimes it makes sense to have multiple managers. You

can think of it this way: Abstract different overall strategies at the manager

level(FlatNetwork vs VlanNetwork), and different implementations at the driver

level(LinuxNetDriver vs CiscoNetDriver).

Managers will often provide methods for initial setup of a host or periodic

tasks to a wrapping service.

This module provides Manager, a base class for managers.


from oslo.config import cfg

from nova.db import base

from nova.openstack.common import log as logging

from nova.openstack.common import periodic_task

from nova import rpc


CONF.import_opt('host', 'nova.netconf')

LOG = logging.getLogger(__name__)

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class Manager(base.Base, periodic_task.PeriodicTasks):

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    def __init__(self, host=None, db_driver=None, service_name='undefined'):

        if not host:

            host = CONF.host

        self.host = host

        self.backdoor_port = None

        self.service_name = service_name

        self.notifier = rpc.get_notifier(self.service_name, self.host)

        self.additional_endpoints = []

        super(Manager, self).__init__(db_driver)

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    def periodic_tasks(self, context, raise_on_error=False):

        """Tasks to be run at a periodic interval."""

        return self.run_periodic_tasks(context, raise_on_error=raise_on_error)

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    def init_host(self):

        """Hook to do additional manager initialization when one requests

        the service be started.  This is called before any service record

        is created.

        Child classes should override this method.



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    def cleanup_host(self):

        """Hook to do cleanup work when the service shuts down.

        Child classes should override this method.



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    def pre_start_hook(self):

        """Hook to provide the manager the ability to do additional

        start-up work before any RPC queues/consumers are created. This is

        called after other initialization has succeeded and a service

        record is created.

        Child classes should override this method.



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    def post_start_hook(self):

        """Hook to provide the manager the ability to do additional

        start-up work immediately after a service creates RPC consumers

        and starts 'running'.

        Child classes should override this method.