Can we pass ENV variables through cmd line while building a docker image through dockerfile?

Question

I am working on a task that involves building a docker image with centOs as its base using a Dockerfile . One of the steps inside the dockerfile needs http_proxy and https_proxy ENV variables to be set in order to work behind the proxy.

As this Dockerfile will be used by multiple teams having different proxies, I want to avoid having to edit the Dockerfile for each team. Instead I am looking for a solution which allows me to pass ENV variables at build time, e.g.,

sudo docker build -e http_proxy=somevalue .

I'm not sure if there is already an option that provides this. Am I missing something?

Answer 1

Containers can be built using build arguments (in Docker 1.9+) which work like environment variables.

Here is the method:

FROM php:7.0-fpm
ARG APP_ENV=local
ENV APP_ENV ${APP_ENV}
RUN cd /usr/local/etc/php && ln -sf php.ini-${APP_ENV} php.ini

and then build a production container:

docker build --build-arg APP_ENV=prod .

For your particular problem:

FROM debian
ENV http_proxy ${http_proxy}

and then run:

docker build --build-arg http_proxy=10.11.24.31 .

Note that if you build your containers with docker-compose, you can specify these build-args in the docker-compose.yml file, but not on the command-line. However, you can use variable substitution in the docker-compose.yml file, which uses environment variables.

Answer 2

I faced the same situation.

According to Sin30's answer pretty solution is using shell,

CMD ["sh", "-c", "cd /usr/local/etc/php && ln -sf php.ini-$APP_ENV php.ini"]