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Customization

An Error Handling Service (EHS) instance can replace selected default behaviours with its own implementations.

Custom resending strategy​

The DefaultResendingStrategy treats all failed messages alike (configurable delay, exponential back-off, maximum retries — see Configuration). If a system needs different resend behaviour per message type or error, it can provide its own implementation of the ResendingStrategy interface as a Spring bean. The implementation receives extensive information about the failed message and returns the next resend time — or an empty result to escalate the error to a permanent error. The DefaultResendingStrategy can serve as a template.

@Component
@Primary
public class CustomResendingStrategy implements ResendingStrategy {

    @Override
    public Optional<ZonedDateTime> determineResend(int errorCountForEvent,
                                                   EventMetadata eventMetadata,
                                                   EventMetadata errorEventMetadata,
                                                   ErrorEventData errorEventData,
                                                   EventMessage message) {
        // ...
    }
}

The @Primary annotation makes Spring prefer the custom bean. For Spring to pick the class up, register it in an auto-configuration: create the file src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports containing the fully qualified class name:

ch.admin.bit.jeap.yoursystem.error.CustomResendingStrategy

Custom task factory​

The definition of the manual tasks created in Agir is done by the DefaultTaskFactory (see Configuration for its properties). Alternatively, a custom TaskFactory implementation can be provided as a Spring bean. Like the custom resending strategy, it must be declared in an auto-configuration to be picked up.

Custom Kafka back-off for EHS consumption retries​

When the EHS itself hits a transient failure while consuming, it retries with a fixed back-off by default:

@Bean(name = KafkaErrorHandlingConfiguration.BACKOFF_BEAN_NAME)
BackOff ehsKafkaErrorHandlingBackOff() {
    return new FixedBackOff(30000, UNLIMITED_ATTEMPTS);
}

An EHS instance can provide its own Spring Kafka BackOff bean under the bean name KafkaErrorHandlingConfiguration.BACKOFF_BEAN_NAME to change this behaviour.