问无法替换Dockerfile中的nginx环境变量

EN

location /my-api/ {
    proxy_pass  ${api_url}/;
}

#base_url comes from system env 
docker build --build-arg base_api_url=$base_url

ARG base_api_url
ENV  api_url=$base_api_url

# This prints the value
RUN echo "api_url= ${api_url}" . 

COPY package.json /usr/src/app/package.json
RUN npm install
COPY . /usr/src/app
RUN npm run build

FROM nginx:1.15.8-alpine
COPY --from=builder /usr/src/app/build /usr/share/nginx/html
EXPOSE 80

# this works
COPY nginx.conf /etc/nginx/nginx.conf.template

# Initially following code was building and deploying docker image and url was hard coded. it was working
# COPY nginx.conf /etc/nginx/conf.d/default.conf 
# Below will start the image but no REST endpoint configured
# CMD ["nginx", "-g", "daemon off;"]

# To substitute the api url few of the many things I have tried.
# Non of the below, have been able to replace the env api_url with its value 
# Actually I don't know -- since /etc/nginx/conf.d/default.conf is not replaced at all

# CMD /bin/bash -c "envsubst < nginx.conf > /etc/nginx/conf.d/default.conf && exec nginx -g 'daemon off;'"
# CMD /bin/sh -c "envsubst < nginx.conf > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;' || cat /etc/nginx/nginx.conf"

# Last status
CMD envsubst < /etc/nginx/nginx.conf.template > /etc/nginx/conf.d/default.conf && exec nginx -g 'daemon off;'

location /my-api/ {
    proxy_pass http://theApiURL;
}

CMD envsubst ${api_url} < /etc/nginx/nginx.conf.template > /etc/nginx/conf.d/default.conf && exec nginx -g 'daemon off;'