Yeah the fact that the backup is itself an idempotent operation means that there's no hazard here due to the interaction with the external system. Even if the second iteration could not detect that the first iteration had completed its work, everything here would be okay. The detection of the file utilized the fact that rename is an atomic operation that itself does indicate complete success.
The problem becomes much trickier if instead the task has non-idempotent side-effects. Coordinating with sending a push-notification for example is a real bummer. Sometimes those sorts of systems will provide a mechanism whereby the publishing of the event is made to be idempotent. For example documentation.onesignal.com/docs/i....
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Yeah the fact that the backup is itself an idempotent operation means that there's no hazard here due to the interaction with the external system. Even if the second iteration could not detect that the first iteration had completed its work, everything here would be okay. The detection of the file utilized the fact that rename is an atomic operation that itself does indicate complete success.
The problem becomes much trickier if instead the task has non-idempotent side-effects. Coordinating with sending a push-notification for example is a real bummer. Sometimes those sorts of systems will provide a mechanism whereby the publishing of the event is made to be idempotent. For example documentation.onesignal.com/docs/i....