#!/usr/bin/python
"""
Picks a host to "create" (boot) a VM on, and does so.

For now, a very dumb algorithm for which host to boot on:
the one with fewer machines running.

TODO: load-balance based on something like actual free RAM

TODO: use a lock to avoid creating the same VM twice in a race
"""


from subprocess import PIPE, Popen, call
import sys
import yaml


def choose_host():
    # Query each of the hosts.
    # TODO get `servers` from a real list of all the VM hosts (instead of
    # hardcoding the list here)
    servers = ['black-mesa.mit.edu', 'sx-blade-2.mit.edu']
    pipes = [(server,
              Popen(['remctl', server, 'remote', 'web', 'info'], stdout=PIPE))
             for server in servers]
    outputs = [(s, p.communicate()[0]) for (s, p) in pipes]
    for (s, p) in pipes:
        if p.returncode != 0:
            raise RuntimeError("remctl to host %s returned non-zero exit status %d"
                               % (s, p.returncode)) 
    results = [(s, yaml.load(o, yaml.CSafeLoader)) for (s, o) in outputs]
    # XXX will the output of 'xm info' always be parseable YAML?

    return max( (int(o['free_memory']), s) for (s, o) in results )[1]


def main(argv):
    if len(argv) < 2:
        print >>sys.stderr, "usage: sipb-xen-remote-create <machine> [<other args...>]"
        return 2
    machine_name = argv[1]
    args = argv[2:]


    p = Popen(['/usr/sbin/sipb-xen-remote-proxy-web', 'listvms'], stdout=PIPE)
    output = p.communicate()[0]
    if p.returncode != 0:
        raise RuntimeError("Command '%s' returned non-zero exit status %d"
                           % ('sipb-xen-remote-proxy-web', p.returncode)) 
    vms = yaml.load(output, yaml.CSafeLoader)

    if machine_name in vms:
        host = vms[machine_name]['host']
        print >>sys.stderr, ("machine '%s' is already running on host %s"
                             % (machine_name, host))
        return 1


    host = choose_host()
    print 'Creating on host %s...' % host
    sys.stdout.flush()
    return call(['remctl', host, 'remote', 'control',
                 machine_name, 'create'] + args)

if __name__ == '__main__':
    sys.exit(main(sys.argv))

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