How does S3 trigger a Lambda function?

Difficulty: 5/10

S3 event notifications, Lambda permissions, Cross-account triggers

S3 Event-Driven Invocation of Lambda

Amazon S3 can trigger a Lambda function automatically in response to specific events like object uploads, deletions, or updates. This allows developers to build serverless, event-driven architectures where file operations directly invoke backend logic without manual polling.

Common S3 Events That Can Trigger Lambda

1
s3:ObjectCreated:* – triggers when an object is uploaded or copied
2
s3:ObjectRemoved:* – triggers when an object is deleted
3
s3:ObjectRestore:* – triggers when an archived object is restored
4
s3:Replication:* – triggers when an object is replicated

Steps to Configure S3 to Trigger Lambda

1
Go to the S3 bucket in the AWS Console
2
Select the 'Properties' tab and find 'Event notifications'
3
Create a new event and specify the event type (e.g., ObjectCreated)
4
Choose 'Lambda function' as the destination
5
Select the Lambda function and grant it permission to be invoked by S3

Sample S3 Event Payload Sent to Lambda

Scenario Questions

0-2 years experience

2-5 years experience

1Our team noticed that a Lambda function isn’t being invoked for certain S3 PUT events. How would you troubleshoot the issue?

Follow-up Questions