Synnefo

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

#

# Redistribution and use in source and binary forms, with or

# without modification, are permitted provided that the following

# conditions are met:

#

#   1. Redistributions of source code must retain the above

#      copyright notice, this list of conditions and the following

#      disclaimer.

#

#   2. Redistributions in binary form must reproduce the above

#      copyright notice, this list of conditions and the following

#      disclaimer in the documentation and/or other materials

#      provided with the distribution.

#

# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR

# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF

# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED

# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN

# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

# POSSIBILITY OF SUCH DAMAGE.

#

# The views and conclusions contained in the software and

# documentation are those of the authors and should not be

# interpreted as representing official policies, either expressed

# or implied, of GRNET S.A.

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):

    has_disk = backend.dfree > vm['disk']

    has_mem = backend.mfree > vm['ram']

    # Consider each VM having 4 Virtual CPUs

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

    # Consider max vcpu/cpu ratio 3

    has_cpu = vcpu_ratio < 3

    return has_cpu and has_disk and has_mem

def backend_score(backend, flavor):

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

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

    cpu_ratio = ((backend.pinst_cnt + 1) * 4) / (backend.ctotal * 3)

    return 0.5 * cpu_ratio + 0.5 * (mem_ratio + disk_ratio)