Event Notifications

📣 What are S3 Event Notifications?

S3 Event Notifications allow you to trigger AWS services (like Lambda, SNS, or SQS) when specific events occur in your S3 bucket — for example:

Example	Trigger
Image uploaded	Trigger a Lambda to resize
Object deleted	Log to SQS for audit
File created in a prefix	Notify a pipeline via SNS

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🔔 Supported Events

Event Name	Triggered When…
s3:ObjectCreated:*	Any object creation (PUT, POST, COPY, etc.)
s3:ObjectCreated:Put	Object uploaded via PUT
s3:ObjectCreated:Post	Uploaded via HTML form
s3:ObjectCreated:CompleteMultipartUpload	Multipart upload completed
s3:ObjectRemoved:*	Object deleted (DELETE or version marker)
s3:ObjectRestore:Completed	Object restore from Glacier completed
s3:Replication:OperationCompletedReplication	Replication success
s3:LifecycleExpiration:*	Object expired due to lifecycle policy

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🎯 Use Cases

Use Case	Triggered Action
Image processing	Trigger Lambda to resize
Document ingestion	Push event to SQS → EC2 batch process
Real-time data pipeline	Notify SNS → Kinesis / analytics service
Logging deletions	Send deleted object info to audit queue
Webhooks / notification bridge	Notify external systems via Lambda

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📦 Destinations You Can Use

Destination	Description
Lambda	Run code in response to event
SQS	Store event in queue
SNS	Publish event to subscribers

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🔧 How to Set Up (Console)

1. Go to your bucket → Properties tab

2. Scroll to Event notifications

3. Click Create event notification

4. Select:

   • Event types (PUT, DELETE, etc.)

   • Prefix/suffix filters (optional)

   • Destination (Lambda, SNS, SQS)

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🧠 Key Points to Remember

Feature	Details
Region-specific	Destination must be in the same region
One destination per rule	You can have multiple rules, each with one destination
Permissions required	Bucket must allow S3 to invoke destination
Filtering supported	By object prefix and/or suffix

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🛠️ Terraform Example: S3 → Lambda

resource "aws_s3_bucket" "bucket" {
  bucket = "yuva-event-demo"
}

resource "aws_lambda_function" "my_lambda" {
  filename         = "lambda.zip"
  function_name    = "s3_event_handler"
  handler          = "index.handler"
  runtime          = "nodejs18.x"
  role             = aws_iam_role.lambda_exec.arn
}

resource "aws_s3_bucket_notification" "bucket_notification" {
  bucket = aws_s3_bucket.bucket.id

  lambda_function {
    lambda_function_arn = aws_lambda_function.my_lambda.arn
    events              = ["s3:ObjectCreated:*"]
    filter_prefix       = "uploads/"
    filter_suffix       = ".jpg"
  }

  depends_on = [aws_lambda_permission.allow_s3]
}

resource "aws_lambda_permission" "allow_s3" {
  statement_id  = "AllowS3Invoke"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.my_lambda.function_name
  principal     = "s3.amazonaws.com"
  source_arn    = aws_s3_bucket.bucket.arn
}

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🛠️ Terraform Example: S3 → SQS

resource "aws_sqs_queue" "event_queue" {
  name = "s3-events-queue"
}

resource "aws_s3_bucket_notification" "sqs_notification" {
  bucket = aws_s3_bucket.bucket.id

  queue {
    queue_arn     = aws_sqs_queue.event_queue.arn
    events        = ["s3:ObjectRemoved:*"]
    filter_prefix = "logs/"
  }
}

Make sure SQS policy allows S3 to send messages.

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📋 Limitations

Limitation	Details
Only one configuration block	Use multiple destinations inside it
Event delivery is best effort	Not guaranteed — use retries or DLQs
Destination must be same region	No cross-region triggers
No multiple destinations per rule	One Lambda/SNS/SQS per rule

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🔎 Testing

Use aws s3 cp to upload a test file and confirm:

aws s3 cp image.jpg s3://yuva-event-demo/uploads/

Check your Lambda logs (CloudWatch) or SQS queue for received event.

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✅ TL;DR Summary

Feature	Value
Event Types	PUT, DELETE, RESTORE, etc.
Destinations	Lambda, SQS, SNS
Filtering	By prefix/suffix
Invocation Region	Destination must be in the same region
Use Cases	Processing, audit, notifications
Retry mechanism	Built-in for Lambda; SQS handles retries

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