So you want your serverless lambda to accept HTTP requests. You got FOUR serverless choices for various definitions of serverless.
- API Gateway - REST style
- API Gateway - HTTP Style
- AppSync - Should have been called GraphQL sync
- ELB, ALB
- Lambda Function URL
Each has a boatload of trade offs.
For Step Functions, you can choose between Step Functions and setting up a server. That's it. Or simulating transactions with choreographed events. Ugly!