Requirement Summary:

Orders are being processedmore than once

Need to preventduplicate processing

Looking forleast implementation effort

Key Concept:

Lambda + Event-driven patternscan occasionally result induplicate invocations(at-least-once delivery model)

You needidempotency(i.e., prevent repeated processing of same event)

Evaluate Options:

✅A. Use DynamoDB for de-duplication

✅Simple and widely used approach

Store a unique orderId as the primary key

Before processing,check if order exists

If yes → skip

If no → process and store the ID

✅Minimal code changes required

B. ECS + Step Functions

❌Overkill for basic de-duplication

Adds significant complexity

C. Retry logic with fixed delay

❌Doesn't prevent duplication —makes it worse

Retrying might trigger thesame message again

D. Athena to identify duplicates

❌Reactive solution, not preventative

Not suitable for real-time event de-duplication

Lambda idempotency:https://docs.aws.amazon.com/lambda/latest/dg/invocation-retries.html

Using DynamoDB for idempotent design:https://aws.amazon.com/blogs/compute/how-to-design-idempotent-APIs-on-aws/