'Set the number of instances for this Instance Group.  An increase in
num_instances will result in VMs being created.  A decrease will result
in VMs being destroyed.
:param  size: Number to instances to resize to.
:type   size: ``int``
:return:  True if successful
:rtype:   ``bool``'

def resize(self, size):

    return self.driver.ex_instancegroupmanager_resize(manager=self, size=size)
