Script in docker file not running - docker

Question

I need to execute a shell script from within Docker. I am not as proficient in Docker or in scripting as I would like to be. The script has no effect and does not print anything to the screen. I do not believe that it is being called.
What am I doing wrong here?
The script should be run as the entrypoint command.
The Script
#!/usr/bin/env bash
set -Ex
function apply_path {
echo "Check that we have ENVIRONMENT_VAR vars"
test -n "$ENVIRONMENT_VAR"
find /usr/src/app/.next \( -type d -name .git -prune \) -o -type f -print0 | xargs -0 sed -i "s#NEXT_PUBLIC_ENVIRONMENT_VAR#$ENVIRONMENT_VAR#g"
}
apply_path
echo "Starting Nextjs"
exec "$#"
The docker file
ARG NODE_VERSION=14.4.0-alpine
###
# STAGE 1: Base
###
FROM node:$NODE_VERSION as base
ENV NODE_PATH=/src
WORKDIR $NODE_PATH
###
# STAGE 2: Build
###
FROM base as build
COPY package.json package-lock.json .npmrc ./
RUN npm i
COPY . ./
RUN NEXT_PUBLIC_ENVIRONMENT_VAR=BUILD npm run build
# Permisions to execute script
RUN ["chmod", "+x", "./entrypoint.sh"]
ENTRYPOINT ["./entrypoint.sh"]
###
# STAGE 3: Production
###
FROM node:$NODE_VERSION
ENV NODE_PATH=/src
ENV APP_PORT=3000
WORKDIR $NODE_PATH
COPY --from=build $NODE_PATH/.next ./.next
COPY --from=build $NODE_PATH/node_modules ./node_modules
COPY --from=build $NODE_PATH/src ./src
COPY --from=build $NODE_PATH/package.json ./
COPY --from=build $NODE_PATH/.babelrc ./
COPY --from=build $NODE_PATH/LICENSE ./
EXPOSE $APP_PORT
CMD npm start

Answer 1

When you have a multi-stage Docker build, the end result of that is only the results starting from the final FROM line. While you're setting that script as an ENTRYPOINT, it's in a previous build stage that's not getting used. ENTRYPOINT (and CMD) don't run at image build time, only when the built image is eventually run.
The easiest way to address this is to COPY the script directly into the final build stage:
# STAGE 3: Production
FROM node:$NODE_VERSION
...
COPY entrypoint.sh .
ENTRYPOINT ["./entrypoint.sh"]
CMD npm start