How do Celery acknowledgements affect task loss and redelivery?

Explains early and late acknowledgement without promising exactly-once task execution.

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A broker keeps a Celery message until the worker acknowledges it. By default, Celery normally acknowledges before execution so a task is less likely to run twice, but work can be lost if the worker dies after that acknowledgement. With acks_late, acknowledgement happens after the task returns, so an interrupted task can be delivered again. That improves recovery only when the task is safe to repeat.

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Explains early and late acknowledgement without promising exactly-once task execution.

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Explains early and late acknowledgement without promising exactly-once task execution.
A broker keeps a Celery message until the worker acknowledges it. By default, Celery normally acknowledges before execution so a task is less likely to run twice, but work can be lost if the worker dies after that acknowledgement. With acks_late, acknowledgement happens after the task returns, so an interrupted task can be delivered again. That improves recovery only when the task is safe to repeat.
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Late acknowledgement does not mean every worker crash automatically causes redelivery under every setting; worker-loss and broker visibility behavior still matter. I choose it together with idempotent effects, sensible time limits, and a broker configuration that matches the longest expected task. The handler records durable progress at boundaries rather than assuming one uninterrupted function call. External API calls need their own idempotency key or reconciliation path.

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Calling acks_late exactly-once delivery
Enabling late acknowledgement for non-idempotent effects
Ignoring broker visibility and worker-loss settings

How do Celery acknowledgements affect task loss and redelivery?

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