You are designing a messaging system by using Pub/Sub to process clickstream data with an event-driven consumer app that relies on a push subscription. You need to configure the messaging system…

Question

Options

• AIncrease the acknowledgement deadline to 10 minutes.
• BUse immediate redelivery as the subscription retry policy, and configure dead lettering to a different topic with maximum delivery attempts set to 10.
• CUse exponential backoff as the subscription retry policy, and configure dead lettering to the same source topic with maximum delivery attempts set to 10.
• DUse exponential backoff as the subscription retry policy, and configure dead lettering to a different topic with maximum delivery attempts set to 10.

• A
  7% (3)
• B
  15% (6)
• C
  2% (1)
• D
  76% (31)

Explanation

Option D satisfies all three requirements simultaneously: exponential backoff retries messages with increasing delays, which prevents thundering-herd overload on a recovering consumer app; dead lettering routes undeliverable messages to a separate topic after 10 attempts, giving you a durable store for inspection without polluting the source.

A is wrong because extending the acknowledgement deadline only delays redelivery timing - it adds no retry policy, no dead lettering, and no protection against overload.

B is wrong because immediate redelivery is the opposite of "gradual" - it hammers a struggling consumer at full speed, directly violating the overload-avoidance requirement.

C is wrong on a subtle but critical point: dead lettering to the same source topic creates an infinite loop - failed messages land back in the source, get picked up, fail again, and cycle forever, making the "10 retry max" meaningless.

Memory tip: The two key words are "gradual" (→ exponential backoff, never immediate) and "store in a topic" (→ dead letter to a different topic, never the source). If either of those is wrong in a choice, eliminate it immediately.

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