Stream the generated image from the GenerateDerivedImage lambda

[deanmoses]

Consider streaming the generated image from the lambda that generates it.

Where I got to

• Streaming from Lambdas sucks because there's no TypeScript bindings
• I managed to stream an image from S3 just fine, but getting a stream from Sharp was not obvious, so I'm backing away from this for now, at least until I get the non-streamed version working.

Why do it

• It'd be faster
• It'd work for my scenario
  • You can progressively stream response payloads through Lambda function URLs, including as an Amazon CloudFront origin, along with using the AWS SDK or using Lambda’s invoke API.
• It'd return bigger images
  • Lambda has a size limit of 6MB on request and response payloads for synchronous invocations, and streaming gets around that
  • There’s a default streaming limit of 20MB. This is a soft limit and can be raised via the Service Quota console or you can raise a support ticket.

Why NOT do it

• Every subsequent request for the image is streamed b/c 1) CloudFront caches the image and even if that fails, 2) CloudFront retrieves the derived image that's now stored in a S3 bucket
• So I won't get a ton of benefit, but it might be nice for Lucie and I who have to hit that generation endpoint
• Why not wait until we have the front end client implemented, and see how much the slowness is noticeable