If instances of an application send ReceiveMessage request at the same time for SQS is it possible for them to receive the same message?

Question

In SQS Standard Queues, if, let us say, 3 instances of the same application are running and cosuming messages from that queue (using long polling), if they send the `ReceiveMessage` request at the exact same time to SQS, is it possible for them to receive the same message?
I'm not talking about at-least-once delivery. The application is idempotent, but I want to know if the `MessageVisibilityTimeout` guarantee that the scenario I described will not occur.

Rodney Lester · Answer

In a distributed system, race conditions can occur that make this possible, or better said, it is not impossible. Idempotency is the solution.

Steve Kinsman · Answer

SQS was designed with the architecture you describe in mind - auto-scaled fleets of worker instances all consuming the same queue are a very common pattern.  Receiving the same message is rare (I've never seen it when looking through logs); there's probably no guarantee though and this possibility is covered by the declared at-least-once delivery.

If instances of an application send ReceiveMessage request at the same time for SQS is it possible for them to receive the same message?

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