S3 event notifications automatically send a message when something happens in a bucket — an object created, deleted, or restored — to targets like Lambda, SNS, SQS, or EventBridge.
The tell
Whenever a scenario is “when a file is uploaded to S3, automatically do X,” that’s an S3 event notification triggering Lambda (process it), SQS (queue it), or SNS (fan out). It’s the glue behind event-driven pipelines built on S3.
Test yourself
Whenever a new object lands in an S3 bucket, a Lambda function must run to process it automatically. What connects the upload to the function?
- A CloudWatch alarm
- An S3 event notification to Lambda
- A scheduled cron job
- A NAT gateway
👉 Click to reveal the answer & explanation
Correct answer: B. An S3 event notification fires on object creation and invokes the Lambda function — the standard event-driven trigger. A CloudWatch alarm (A) watches metrics; a cron job (C) polls on a schedule (adds latency); NAT (D) is networking.
Related topics
Amazon S3 · AWS Lambda · Amazon EventBridge
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