SAM Lambda Function make file to support node_modules in Layers

makefile

##
# Custom SAM Build function to support ES modules in Lambda Layers
# 
# SAM deploy does not support symlinks in Lambda Functions, it tries to follow them at deploy time
# This means you cant build a function with a symlink to the node_modules of a layer  - which you need to do to support ES modules
# @see https://github.com/vibe/aws-esm-modules-layer-support
#
# This works by packaging the function code as SAM does using `npm pack`, but then we insert a symlink to the layers node_modules
# And then create a zip *including* the symlink to the layer.
#
# By renaming the zip file to match the ARCHIVE_PATH SAM will still find the built source, but as its already a zip it wont try to package it 
#
# Rename MyLambdaFunction to mach the Logical ID of your Lambda Function  
build-MyLambdaFunction:
  # package the same way SAM does using npm pack (which supports .npmignore files etc), saving the resulting archive name as ARCHIVE 
	$(eval ARCHIVE_PATH=$(shell npm pack))
  # Unpack again so we can make it Lambda compatible
	tar -xzvf "$(ARCHIVE_PATH)"
  # Insert our symlink to layer node modules
	ln -s /opt/nodejs/node_modules package/node_modules
  # create a zip with no root folder (npm pack adds a 'package' root folder that we dont want)
	cd package && zip -ry ../lambdaFunctionSrc.zip .
  # delete the ARTIFACTS_DIR created by SAM
	rm -rf "$(ARTIFACTS_DIR)"
  # replace ARTIFACTS_DIR with our ZIP file 
	mv lambdaFunctionSrc.zip "$(ARTIFACTS_DIR)"