how to override the files in docker container - docker

Question

I have below dockerfile:
FROM node:16.7.0
ARG JS_FILE
ENV JS_FILE=${JS_FILE:-"./sum.js"}
ARG JS_TEST_FILE
ENV JS_TEST_FILE=${JS_TEST_FILE:-"./sum.test.js"}
WORKDIR /app
# Copy the package.json to /app
COPY ["package.json", "./"]
# Copy source code into the image
COPY ${JS_FILE} .
COPY ${JS_TEST_FILE} .
# Install dependencies (if any) in package.json
RUN npm install
CMD ["sh", "-c", "tail -f /dev/null"]
after building the docker image, if I tried to run the image with the below command, then still could not see the updated files.
docker run --env JS_FILE="./Scripts/updated_sum.js" --env JS_TEST_FILE="./Test/updated_sum.test.js" -it <image-name>
I would like to see updated_sum.js and updated_sum.test.js in my container, however, I still see sum.js and sum.test.js.
Is it possible to achieve this?
This is my current folder/file structure:
.
-->Dockerfile
-->package.json
-->sum.js
-->sum.test.js
-->Test
-->--->updated_sum.test.js
-->Scripts
-->--->updated_sum.js

Answer 1

Using Docker generally involves two phases. First, you compile your application into an image, and then you run a container based on that image. With the plain Docker CLI, these correspond to the docker build and docker run steps. docker build does everything in the Dockerfile, then stops; docker run starts from the fixed result of that and runs the image's CMD.
So if you run
docker build -t sum .
The sum:latest image will have the sum.js and sum.test.js files, because that's what the Dockerfile COPYs in. You can then
docker run --rm sum \
ls
docker run --rm sum \
node ./sum.js
to see and run the contents of the image. (Specifying the latter command as CMD would be a better practice.) You can run the command with different environment variables, but it won't change the files in the image:
docker run --rm -e JS_FILE=missing.js sum ls
# still only has sum.js
docker run --rm -e JS_FILE=missing.js node missing.js
# not found
Instead you need to rebuild the image, using docker build --build-arg options to provide the values
docker build \
--build-arg JS_FILE=./product.js \
--build-arg JS_TEST_FILE=./product.test.js \
-t product \
.
docker run --rm product node ./product.js
The extremely parametrizable Dockerfile you show here can be a little harder to work with than a single-purpose Dockerfile. I might create a separate Dockerfile per application:
# Dockerfile.sum
FROM node:16.7.0
WORKDIR /app
COPY package*.json .
RUN npm ci
COPY sum.js sum.test.js .
CMD node ./sum.js
Another option is to COPY the entire source tree into the image (Javascript files are pretty small compared to a complete Node installation) and use a docker run command to pick which script to run.