In a microservice consuming events from a message queue, what happens if the consumer is not idempotent and the same event is delivered twice due to a retry?

medium📝 Analysis Q5 of 15

Microservices - Event-Driven Architecture

AThe consumer crashes due to duplicate event IDs

BThe event is processed twice, possibly causing duplicate side effects

CThe second event is automatically ignored by the message queue

DThe event is merged with the first event automatically

Step-by-Step Solution

Solution:

Step 1: Understand non-idempotent consumer behavior
Without idempotency, the consumer processes every event as new, even duplicates.
Step 2: Identify consequences of duplicate processing
This can cause duplicate database writes, inconsistent state, or repeated side effects.
Final Answer:
The event is processed twice, possibly causing duplicate side effects -> Option B
Quick Check:
Non-idempotent = Duplicate side effects [OK]

Quick Trick: No idempotency means duplicates cause repeated effects [OK]

Common Mistakes:

MISTAKES

Assuming message queue filters duplicates
Thinking consumer crashes on duplicates
Believing events merge automatically

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More Microservices Quizzes

In a microservice consuming events from a message queue, what happens if the consumer is not idempotent and the same event is delivered twice due to a retry?

Step 1: Understand non-idempotent consumer behavior

Step 2: Identify consequences of duplicate processing

Final Answer:

Quick Check:

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