Custom CMD handler based on environment variables

Dockerfile

FROM public.ecr.aws/lambda/python:3.9

ARG HANDLER_PATH="src.entrypoints.listener.handler.handler"
ENV HANDLER_PATH="${HANDLER_PATH}"

#....

ENTRYPOINT [ "./lambda-entrypoint.sh" ]

lambda-entrypoint.sh

#!/usr/bin/env bash

# shellcheck disable=SC2034
export _HANDLER="${HANDLER_PATH}"

RUNTIME_ENTRYPOINT=/var/runtime/bootstrap

if [ -z "${AWS_LAMBDA_RUNTIME_API}" ]; then
  exec /usr/local/bin/aws-lambda-rie $RUNTIME_ENTRYPOINT
else
  exec $RUNTIME_ENTRYPOINT
fi