Synnefo

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

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from __future__ import division

import logging

log = logging.getLogger(__name__)

def allocate(backends, vm):

    if len(backends) == 1:

        return backends[0]

    # Filter those that can not host the vm

    capable_backends = [backend for backend in backends

                        if vm_fits_in_backend(backend, vm)]

    log.debug("Capable backends for VM %s: %s", vm, capable_backends)

    # Since we are conservatively updating backend resources on each

    # allocation, a backend may actually be able to host a vm (despite

    # the state of the backend in db)

    if not capable_backends:

        capable_backends = backends

    # Compute the scores for each backend

    backend_scores = [(backend, backend_score(backend, vm))

                      for backend in capable_backends]

    log.debug("Backend scores %s", backend_scores)

    # Pick out the best

    result = min(backend_scores, key=lambda (b, b_score): b_score)

    backend = result[0]

    return backend

def vm_fits_in_backend(backend, vm):

    return backend.dfree > vm['disk'] and backend.mfree > vm['ram']

def backend_score(backend, flavor):

    mratio = 1 - (backend.mfree / backend.mtotal)

    dratio = 1 - (backend.dfree / backend.dtotal)

    cratio = (backend.pinst_cnt + 1) / (backend.ctotal * 4)

    return 0.7 * (mratio + dratio) * 0.3 * cratio