Build the docker image with environment variables

Question

so the objective is to have a different image for prod and testing so there are certain variables change accordingly so I need to set env variables during the build.

# Dockerfile
ENV Somename: $value
...

docker build --build-arg Somename=value -t test .

docker run -d -p port:port test

this work flow is not taking the env variables

Answer 1

First you need to consume the build-arg inside you dockerfile using the ARG command.

FROM alpine

# consume the build arg    
ARG somename  

# persist the env variable in the built image
ENV somename=$somename  

# somename will appear as an env variable
RUN echo $somename 
RUN env

And running the build command docker build --build-arg somename=hello . will show you an env variable somename=hello