Environment variables inside Dockerfile

Question

New to docker as you noticed. I'm trying to build a docker image with me assigning the current GID/UID to the usermod/groupmod command that I will run inside the docker image.

I tried the command with environement variables but It didnt work

the 1002 and 1003 is the user GID/UID of the connected user

FROM mongo:4.4.9

# setup folder before switching to user
RUN mkdir /var/lib/mongo
RUN usermod -u 1002 mongodb
RUN groupmod -g 1003 mongodb
RUN chown mongodb:mongodb /var/lib/mongo
RUN chown mongodb:mongodb /var/log/mongodb

USER mongodb

I tried this :

FROM mongo:4.4.9

ENV MONGO_UID=$MONGO_UID
ENV MONGO_GID=$MONGO_GID

# setup folder before switching to user
RUN mkdir /var/lib/mongo
RUN usermod -u $MONGO_UID mongodb
RUN groupmod -g $MONGO_GID mongodb
RUN chown mongodb:mongodb /var/lib/mongo
RUN chown mongodb:mongodb /var/log/mongodb

USER mongodb

and building by this :

docker build --build-arg MONGO_UID=1002 --build-arg MONGO_GID=1003 .

Thanks for any help !

Answer 1

You need to declare them as an argument and not as an environment variable, since you are passing an argument to the docker build command as a --build-arg argument value.

The Dockerfile should be something like this:

FROM mongo:4.4.9

ARG MONGO_UID
ARG MONGO_GID

# setup folder before switching to user
RUN mkdir /var/lib/mongo
RUN usermod -u ${MONGO_UID} mongodb
RUN groupmod -g ${MONGO_GID} mongodb
RUN chown mongodb:mongodb /var/lib/mongo
RUN chown mongodb:mongodb /var/log/mongodb

USER mongodb

If you need to have them as an environment variable inside the container, then you would need to say that the ENV is equal to the ARG:

ARG MONGO_UID
ENV MONGO_UID=${MONGO_UID}

It's also possible to give the argument (same to ENV) a default value, in case you are interested:

ARG MONGO_UID=default

Not having a default value will force the user to supply a value to the argument.