Synnefo

# Copyright 2011 GRNET S.A. All rights reserved.

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import logging

import datetime

from django.utils import importlib

from synnefo import settings

from synnefo.db.models import Backend

from synnefo.logic.backend import update_resources

log = logging.getLogger(__name__)

class BackendAllocator():

    """Wrapper class for instance allocation.

    """

    def __init__(self):

        self.strategy_mod =\

            importlib.import_module(settings.BACKEND_ALLOCATOR_MODULE)

    def allocate(self, flavor):

        """Allocate a vm of the specified flavor to a backend.

        Warning!!: An explicit commit is required after calling this function,

        in order to release the locks acquired by the get_available_backends

        function.

        """

        # Get the size of the vm

        disk = flavor_disk(flavor)

        ram = flavor.ram

        cpu = flavor.cpu

        vm = {'ram': ram, 'disk': disk, 'cpu': cpu}

        log.debug("Allocating VM: %r", vm)

        # Refresh backends, if needed

        refresh_backends_stats()

        # Get available backends

        available_backends = get_available_backends()

        if not available_backends:

            return None

        # Find the best backend to host the vm, based on the allocation

        # strategy

        backend = self.strategy_mod.allocate(available_backends, vm)

        log.info("Allocated VM %r, in backend %s", vm, backend)

        # Reduce the free resources of the selected backend by the size of

        # the vm

        reduce_backend_resources(backend, vm)

        return backend

def get_available_backends():

    """Get available backends from db.

    """

    return list(Backend.objects.select_for_update().filter(drained=False,

                                                           offline=False))

def flavor_disk(flavor):

    """ Get flavor's 'real' disk size

    """

    if flavor.disk_template == 'drbd':

        return flavor.disk * 1024 * 2

    else:

        return flavor.disk * 1024

def reduce_backend_resources(backend, vm):

    """ Conservatively update the resources of a backend.

    Reduce the free resources of the backend by the size of the of the vm that

    will host. This is an underestimation of the backend capabilities.

    """

    new_mfree = backend.mfree - vm['ram']

    new_dfree = backend.dfree - vm['disk']

    backend.mfree = 0 if new_mfree < 0 else new_mfree

    backend.dfree = 0 if new_dfree < 0 else new_dfree

    backend.pinst_cnt += 1

    backend.save()

def refresh_backends_stats():

    """ Refresh the statistics of the backends.

    Set db backend state to the actual state of the backend, if

    BACKEND_REFRESH_MIN time has passed.

    """

    now = datetime.datetime.now()

    delta = datetime.timedelta(minutes=settings.BACKEND_REFRESH_MIN)

    for b in Backend.objects.filter(drained=False, offline=False):

        if now > b.updated + delta:

            log.debug("Updating resources of backend %r", b)

            update_resources(b)