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An application sends events to an SQS queue. Suddenly the queue's `ApproximateNumberOfMessagesVisible` grows steadily. Which Lambda metric should the team check FIRST?
AThe consumer Lambda's `Throttles` metric — if it's throttling, the queue backs up
BCloudFront's bytes-cached metric
CRoute 53's healthy-host count
DThe producer's `BytesUploaded` to S3
Answer & Solution
Correct answer: A. The consumer Lambda's `Throttles` metric — if it's throttling, the queue backs up
Lambda Throttles = invocations rejected due to concurrency limit (account or function reserved). Throttling consumers → queue grows. The other metrics are unrelated to SQS-consumer throughput.
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