':param  id: Internal identifier of Instance Group.  Display only.
:type   id: ``str``
:param  name: The name of this Instance Group.
:type   name: ``str``
:param  zone: Zone in witch the Instance Group belongs
:type   zone: :class: ``GCEZone``
:param  size: Number of instances in this Instance Group.
:type   size: ``int``
:param  template: An initialized :class:``GCEInstanceTemplate``
:type   driver: :class:``GCEInstanceTemplate``
:param  instance_group: An initialized :class:``GCEInstanceGroup``
:type   driver: :class:``GCEInstanceGroup``
:param  driver: An initialized :class:``GCENodeDriver``
:type   driver: :class:``GCENodeDriver``
:param  extra: A dictionary of extra information.
:type   extra: ``dict``'

def __init__(self, id, name, zone, size, template, instance_group, driver, extra=None):

    self.id = str(id)
    self.name = name
    self.zone = zone
    self.size = (size or 0)
    self.template = template
    self.instance_group = instance_group
    self.driver = driver
    self.extra = extra
    UuidMixin.__init__(self)
