'Create an AWS instance with the given parameters.
Return either boto.ec2.instance object or None if the instance
could not be created.'

def _run_nodes(self, count, image_id, size, diskmap):

    with start_action(action_type=u'flocker:provision:aws:create_node:run_nodes', instance_count=count):
        reservation = self._connection.run_instances(image_id, min_count=1, max_count=count, key_name=self._keyname, instance_type=size, security_groups=self._security_groups, block_device_map=diskmap, placement=self._zone)
        return reservation.instances
