Amazon's hand an answer to that with FIFO queues for the better part of years, but even without a queue based system you probably still need some notion of idem

Amazon's hand an answer to that with FIFO queues for the better part of years, but even without a queue based system you probably still need some notion of idempotence in the actions your system takes. Systems "without queues" have just eschewed one queue for N queues, where N is the number of clients buffering actions for retries at any given moment.