Add comment about CORS in todos-lambda

[natanrolnik]

While testing something with a lambda, I noticed I had twice the Access-Control-Allow-Origin header, and it led to CORS errors when calling my lambda function from the browser.

Upon investigation, I found that it was due to CORS being set both at the code level, and at the Lambda function URL configuration level. When it's configured in the Lambda URL, there's no need to setup CORSMiddleware.

This PR adds a comment about it in the todos-lambda sample project.

[adam-fowler]

You should make it clear this is APIGateway (maybe add a link), otherwise this is cool.

[natanrolnik]

@adam-fowler so I also thought this is APIGateway when I first saw it, but it turns out it's not exactly API Gateway (at least not publicly):

https://docs.aws.amazon.com/lambda/latest/dg/urls-configuration.html
https://www.serverlessguru.com/blog/aws-lambda-function-urls-vs-amazon-api-gateway

I could link to this section in the first link, what do you think?

https://docs.aws.amazon.com/lambda/latest/dg/urls-configuration.html#urls-cors

[adam-fowler]

We use APIGateway to access Lambda’s not function URLs. So I would have thought it would be related to this https://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-cors.html. Did you check the APIGateway CORS setup after deployment?

[adam-fowler]

Out of interest what is the input to the lambda if you use a function URLs?

[natanrolnik]

Did you check the APIGateway CORS setup after deployment?

I checked API Gateway, and there's no entry there for this function - it's all handled by Lambda:

Here's where it's defined:

Out of interest what is the input to the lambda if you use a function URLs?

If I understand the question correctly, the input is still a APIGatewayV2Request.