What is the difference between SQS and SNS?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of AWS conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
SQS is a queue; SNS is a publish and subscribe topic. They solve different problems and are often combined.
- SQS is point-to-point. A message is stored until a consumer processes and deletes it. It supports visibility timeouts, dead-letter queues, and FIFO ordering. One message is handled by one consumer.
- SNS is fan-out. A publisher sends a message to a topic and it is pushed to all subscribers, including SQS queues, Lambda, HTTP endpoints, and email. There is no storage or retry beyond the delivery policy.
aws sns publish --topic-arn arn:aws:sns:us-east-1:111122223333:orders \
--message '{"orderId":"42"}'
A common pattern is an SNS topic that fans out to several SQS queues so independent services each process a copy. Use SQS alone for work queues and SNS alone for notifications.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.