private static <T> T validated(final String configKey, final T value) {
        final ConfigDef.Validator validator = StreamsConfig.configDef().configKeys().get(configKey).validator;
        if (validator != null) {
            validator.ensureValid(configKey, value);
        }
        return value;
    }
The rack-aware assignment strategy as configured via
{@link StreamsConfig#RACK_AWARE_ASSIGNMENT_STRATEGY_CONFIG}
streams/src/main/java/org/apache/kafka/streams/processor/assignment/AssignmentConfigs.java