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Docker container - what's the best practice to inject to it a sensitive data

I have a service that sends emails. I'd rather not to keep my Gmail password in any file. After googling I found that I can provide environment variables to the containers with --build-arg param while building them.

The Dockerfile file

FROM node:latest
ARG buildtime_variable=default_value
ENV env_var_name=$buildtime_variable
...
CMD [ "node", "dist/server.js" ]

The build command

$ docker build --build-arg buildtime_variable=new_value .

List environment variables in running container

$ docker exec app env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=38dd21dbeda3
NODE_VERSION=11.10.0
YARN_VERSION=1.13.0
env_var_name=default_value
HOME=/root

Why as a result the env_var_name still equal to default_value or how I can inject the new_value to the container?

Thanks a lot for each answer!

Solution

  • Just use the docker-compose instead of docker command:

    docker-compose build --build-arg buildtime_variable=new_value <container name>

    Enjoy!