apache/flink · error · IllegalArgumentException

Unknown restart strategy

Error message

Unknown restart strategy {restartStrategyName}.

What it means

Thrown by RestartStrategyDescriptionUtils when resolving the human-readable description for a restart-strategy name that is not one of the recognized RestartStrategyType values (no, fixed-delay, failure-rate, exponential-delay). The lambda maps known types to descriptions and throws for anything else. It indicates the configuration or caller supplied an unrecognized restart strategy name.

Solutions

1. Use one of the documented names: no, fixed-delay, failure-rate, exponential-delay (case-insensitive).
2. If relying on the cluster default, leave restart-strategy.name unset instead of passing an invalid value.
3. Validate the configured name against RestartStrategyType.of(...) before asking for a description, surfacing a clear config error.

Example fix

// before
// restart-strategy.name: fixeddelay  (typo)
// after
# in flink-conf.yaml or job config
restart-strategy.name: fixed-delay
restart-strategy.fixed-delay.attempts: 3

Set<String> valid = Set.of("no","fixed-delay","failure-rate","exponential-delay");
if (!valid.contains(restartStrategyName.toLowerCase())) {
    throw new IllegalArgumentException("Unknown restart strategy: " + restartStrategyName);
}

public static boolean isKnownRestartStrategy(String name) {
    try { RestartStrategyOptions.RestartStrategyType.of(name.toLowerCase()); return true; }
    catch (Exception e) { return false; }
}

When it happens

Trigger: Calling RestartStrategyDescriptionUtils.getRestartStrategyDescription with a name not matching any RestartStrategyType.of(...) case; setting restart-strategy.name to a typo or a removed strategy name.

Common situations: Config typo like 'fixed_deLay'; using a strategy name valid in an older Flink version that was removed; custom code building the description string from raw config without validation.

Related errors

• argument is an empty- or whitespace-only string
• Cannot create local tmp dir
• Cannot parse ApplicationID from
• Cannot parse JobID from
• Could not configure serializers from

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/3f6fe3fc34fe4c62. Report an issue: GitHub.

Appendix: source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/RestartStrategyDescriptionUtils.java:57

    public static String getRestartStrategyDescription(Configuration configuration) {
        final Optional<String> restartStrategyNameOptional =
                configuration.getOptional(RestartStrategyOptions.RESTART_STRATEGY);

        return restartStrategyNameOptional
                .map(
                        restartStrategyName -> {
                            switch (RestartStrategyOptions.RestartStrategyType.of(
                                    restartStrategyName.toLowerCase())) {
                                case NO_RESTART_STRATEGY:
                                    return "Restart deactivated.";
                                case FIXED_DELAY:
                                    return getFixedDelayDescription(configuration);
                                case FAILURE_RATE:
                                    return getFailureRateDescription(configuration);
                                case EXPONENTIAL_DELAY:
                                    return getExponentialDelayDescription(configuration);
                                default:
                                    throw new IllegalArgumentException(
                                            "Unknown restart strategy "
                                                    + restartStrategyName
                                                    + ".");
                            }
                        })
                .orElse("Cluster level default restart strategy");
    }

    private static String getExponentialDelayDescription(Configuration configuration) {
        Duration initialBackoff =
                configuration.get(
                        RestartStrategyOptions.RESTART_STRATEGY_EXPONENTIAL_DELAY_INITIAL_BACKOFF);
        Duration maxBackoff =
                configuration.get(
                        RestartStrategyOptions.RESTART_STRATEGY_EXPONENTIAL_DELAY_MAX_BACKOFF);
        double backoffMultiplier =
                configuration.get(
                        RestartStrategyOptions

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