def METHOD_NAME(properties, cluster, image, instance_group):
    """ Assign instance group config to the cluster. """
    group_spec = properties.get(instance_group)
    group_schema = NODES_SCHEMA
    group_config = get_instance_group_config(group_spec, image, group_schema)
    config_name = instance_group + 'Config'
    cluster['properties']['config'][config_name] = group_config
    config_output_path = 'ref.{}.config.{}'.format(cluster['name'], config_name)
    return {
        'name': '{}InstanceNames'.format(instance_group),
        'value': '$({}.instanceNames)'.format(config_output_path)
    }