It happened to all of us. You order a shiny new tech gadget or a pair of new jeans online.
The order takes its time and then fails due to momentary network failure. So you submit it again, and the order goes through this time; success!
However, two weeks later, you realize your credit card was charged twice by mistake.
Why did it happen?
It happened because the shop’s orders API did not implement API idempotency correctly.
And that’s the subject of today’s post.
In this post, you will learn about serverless API idempotency, why it’s essential, and how to implement it in a sample serverless “orders” service with AWS Lambda functions, AWS CDK, and AWS Lambda Powertools for Python. We will also write an end-to-end test to validate that API idempotency works as expected.