SAA-C03 at-least-once delivery Practice Question
A patient portal must process every event at least once, but duplicate processing is acceptable if the consumer handles idempotency. Which eventing approach is most suitable? The team wants the control to be enforceable during normal operations.
⚠ Common exam trap
Test-takers frequently confuse 'at-least-once' delivery with 'exactly-once' delivery, or incorrectly assume that UDP or in-memory queues can provide reliable event processing, when in fact only a managed queue service like SQS with idempotent consumers meets the stated requirement for enforceability during normal operations.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Amazon SQS standard queue and design consumers to be idempotent
Amazon SQS standard queues provide at-least-once delivery, ensuring every event is processed at least once, which matches the requirement. Duplicate processing is acceptable because the team can design consumers to be idempotent, handling duplicates without side effects. SQS is a fully managed, scalable, and durable service that enforces this behavior during normal operations without requiring custom infrastructure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use an in-memory queue on one EC2 instance
Why it's wrong here
An in-memory queue on a single EC2 instance is lost on restart and cannot guarantee at-least-once delivery across failures. It is tempting for simple low-latency buffering, which suits ephemeral workloads, but durable eventing needs a managed queue that persists messages.
- ✗
Use UDP messages sent directly to workers
Why it's wrong here
UDP does not provide durable at-least-once delivery.
- ✓
Use Amazon SQS standard queue and design consumers to be idempotent
Why this is correct
Amazon SQS standard queues guarantee at-least-once delivery, so no event is lost, and duplicates are possible; consumers must therefore be idempotent. This satisfies the stated requirement that duplicate processing is acceptable if consumers handle idempotency.
- ✗
Use CloudFront signed URLs
Why it's wrong here
Signed URLs authorise time-limited access to CloudFront content; they neither deliver events to consumers nor enforce at-least-once processing. They are tempting because they control access to distributed content, which suits protecting private media downloads, not event delivery with retries.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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