What Happens to an S3 Event When Lambda Times Out with Default Settings?
A company processes incoming documents from an Amazon S3 bucket. Users upload documents to an S3 bucket using a web user interface. Upon receiving files in S3, an AWS Lambda function is invoked to process the files, but the Lambda function times out intermittently. If the Lambda function is configured with the default settings, what will happen to the S3 event when there is a timeout exception?
Community Insight
The exam tests the default retry-and-discard behavior of asynchronous Lambda invocations — the trap is assuming a Dead Letter Queue or endless retries exist by default.
Amazon S3 invokes Lambda asynchronously, and with default settings Lambda retries a failed event twice (three total attempts) before discarding it. The community consensus is answer D, backed by AWS documentation on asynchronous error handling.
Many candidates choose B because they assume Lambda ships with a default Dead Letter Queue; in reality, a DLQ (or on-failure destination) must be explicitly configured, so with defaults the event is simply discarded after two retries.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
Amazon S3 invokes Lambda asynchronously, and for asynchronous invocations Lambda automatically retries the event twice more (a total of three attempts) with a delay of one to two minutes between attempts. If the function still fails after these retries and no Dead Letter Queue or on-failure destination is configured, Lambda discards the event. This matches option D exactly. Community comment [1] (5 likes) spells out this behavior clearly, and comment [2] links the official AWS documentation confirming it.Why the Other Options Are Wrong
Option A is wrong because Lambda does not send SNS email notifications for failed events by default; you would have to explicitly configure a destination such as SNS. Option B is wrong because there is no default Dead Letter Queue — a DLQ must be deliberately configured on the function. Option C is wrong because Lambda does not retry indefinitely; asynchronous invocations are limited to exactly two retries before the event is dropped. Only D reflects the true default behavior.Community Comment Notes
The community is unanimous that D is correct. Comment [1], the most upvoted, explains that Lambda makes two additional attempts (three total) and then discards the event when no DLQ or destination exists. Comment [2] reinforces this with a direct citation of the AWS Lambda developer guide on asynchronous invocation error handling, which is the authoritative source for this behavior.Official Reference
Exam Strategy
Memorize the default behavior of asynchronous invocations (S3, SNS, EventBridge): two automatic retries, then the event is discarded unless a DLQ or on-failure destination was explicitly configured. When a question says 'default settings,' rule out any option involving DLQs, SNS emails, or infinite retries. This pattern appears frequently in DVA-C02, so knowing '2 retries then discard' earns quick points.
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