Reference Shell Script Variable in Dockerfile - docker

Question

I have a config.sh:
IMAGE_NAME="back_end"
APP_PORT=80
PUBLIC_PORT=8080
and a build.sh:
#!/bin/bash
source config.sh
echo "Image name is: ${IMAGE_NAME}"
sudo docker build -t ${IMAGE_NAME} .
and a run.sh:
#!/bin/bash
source config.sh
# Expose ports and run
sudo docker run -it \
-p $PUBLIC_PORT:$APP_PORT \
--name $IMAGE_NAME $IMAGE_NAME
and finally, a Dockerfile:
...
CMD ["gunicorn", "-b", "0.0.0.0:${APP_PORT}", "main:app"]
I'd like to be able to reference the APP_PORT variable in my config.sh within the Dockerfile as shown above. However, what I have does not work and it complains: Error: ${APP_PORT} is not a valid port number. So it's not interpreting APP_PORT as a variable. Is there a way to reference the variables within config.sh from within the Dockerfile?
Thanks!
EDIT: New Files based on suggested solutions (still don't work)
I have a config.sh:
IMAGE_NAME="back_end"
APP_PORT=80
PUBLIC_PORT=8080
and a build.sh:
#!/bin/bash
source config.sh
echo "Image name is: ${IMAGE_NAME}"
sudo docker build --build-arg APP_PORT="${APP_PORT}" -t "${IMAGE_NAME}" .
and a run.sh:
#!/bin/bash
source config.sh
# Expose ports and run
sudo docker run -it \
-p $PUBLIC_PORT:$APP_PORT \
--name $IMAGE_NAME $IMAGE_NAME
and finally, a Dockerfile:
FROM python:buster
LABEL maintainer="..."
ARG APP_PORT
#ENV PORT $APP_PORT
ENV APP_PORT=${APP_PORT}
#RUN echo "$PORT"
# Install gunicorn & falcon
COPY requirements.txt ./
RUN pip3 install --no-cache-dir -r requirements.txt
# Add demo app
COPY ./app /app
COPY ./config.sh /app/config.sh
WORKDIR /app
RUN ls -a
CMD ["gunicorn", "-b", "0.0.0.0:${APP_PORT}", "main:app"]
run.sh still fails and reports: Error: '${APP_PORT} is not a valid port number.'

Answer 1

Define a variable in Dockerfile as follows:
FROM python:buster
LABEL maintainer="..."
ARG APP_PORT
ENV APP_PORT=${APP_PORT}
# Install gunicorn & falcon
COPY requirements.txt ./
RUN pip3 install --no-cache-dir -r requirements.txt
# Add demo app
COPY ./app /app
COPY ./config.sh /app/config.sh
WORKDIR /app
CMD gunicorn -b 0.0.0.0:$APP_PORT main:app # NOTE! without separating with ["",""]
Pass it as build-arg, e.g. in your build.sh:
Note! Passing build argument is only necessary when it is used for building docker image. You use it on CMD and one can omit passing it during building docker image.
#!/bin/bash
source config.sh
echo "Image name is: ${IMAGE_NAME}"
sudo docker build --build-arg APP_PORT="${APP_PORT}" -t "${IMAGE_NAME}" .
# sudo docker build --build-arg APP_PORT=80 -t back_end . -> You may omit using config.sh and directly define the value of variables
and pass value of $APP_PORT in run.sh as well when starting the container:
#!/bin/bash
source config.sh
# Expose ports and run
sudo docker run -it \
-e APP_PORT=$APP_PORT \
-p $PUBLIC_PORT:$APP_PORT \
--name $IMAGE_NAME $IMAGE_NAME

Answer 2

You need a shell to replace environment variables and when your CMD is in exec form, there's no shell.
If you use the shell form, there is a shell and you can use environment variables.
CMD gunicorn -b 0.0.0.0:${APP_PORT} main:app
Read here for more information on the two forms of the CMD statement: https://docs.docker.com/engine/reference/builder/#cmd