RuntimeDependenciesLayer rebuilding on every API request

First of all, thank you @Envek and others for both the great writeup at https://evilmartians.com/chronicles/serverless-typescript-a-complete-setup-for-aws-sam-lambda and for this template repo.

This is my first time using AWS SAM in general, and it’s been tricky with Typescript.

Problem

When running sam local start-api, every request I make to http://127.0.0.1:3000/ triggers a rebuild of the dependency layer.

Steps to reproduce

• Clone fresh copy of repo and walk through the setup
• sam local start-api
• Visit http://127.0.0.1:3000/

The first visit will build the image as expected.

When refreshing the browse, based on this comment, I would expect the image not to rebuild since no source code would have changed.

However, on each request, the image appears to be rebuilt with the following log line:

RuntimeDependenciesLayer is a local Layer in the template

The time it takes to rebuild this image makes it difficult to develop my frontend.

The workaround I have right now is to just point my frontend at my dev environment in AWS, but I’d prefer to be able to run both front & backend locally.

[justintilson]

One way I found that changes this behavior is to include the --warm-containers=EAGER flag when starting your local SAM API. Example:

sam local start-api --docker-network your-network --env-vars=env.json --warm-containers=EAGER

From: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-cli-command-reference-sam-local-start-api.html with some more relevant tidbits here: https://aws.amazon.com/blogs/compute/working-with-aws-lambda-and-lambda-layers-in-aws-sam/

[ahurlburt]

@Envek done: https://github.com/aws/aws-sam-cli/issues/3725

Maybe people coming across this can upvote 😃