When elm-serverless failed to materialise for 0.19 I assumed it was due to native code restrictions. I missed this package as I have some AWS Lambda functions I wanted to upgrade and continue to work on in 0.19. I checked the source code and found that it only uses ports, it just needed the upgrade work done.
The original work on this was done by @ktonon for Elm 0.18: elm-serverless for Elm 0.18.
Check it out if you want to experiment with an Elm back-end deployed in the cloud.