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Retry logic

Exponential backoff Dead-letter queue DLQ

Pattern for handling temporary failures in distributed systems - automatic retry with exponential backoff.

Definition

Retry logic is a fundamental pattern in distributed systems and integrations: when an operation fails (network error, timeout, temporary unavailability), the system automatically retries after a waiting period. Exponential backoff is the standard: first retry after 1 second, next after 2, then 4, 8, and so on - with a cap (e.g. 5 minutes). This prevents an overloaded system from being bombarded with retries and collapsing further (the thundering herd problem). A Dead-Letter Queue (DLQ) is where messages end up after the maximum number of retries - they are parked for manual inspection rather than disappearing. In Elhub integrations, retry logic is especially critical: Elhub has strict deadlines and can reject messages for many reasons. A message rejected due to a validation error should not be retried blindly - it requires human intervention.

In practice

In practice, retry logic and dead-letter queues are two of the most important elements in a robust Elhub integration. SAMTYGD monitors message queues continuously: messages that fail are placed in the DLQ with error code and context, and the operations team is notified. An E01 message (supplier switch) rejected by Elhub cannot be retried automatically - the cause must be investigated (incorrect metering point ID, invalid switch date, existing active process). Without robust DLQ handling, rejected messages disappear silently, and the supplier switch fails without anyone being aware.

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Retry logic

Definition

In practice

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