I am working on a docker image I created using firesh/nginx-lua (The Linux distribution is Alpine):

FROM firesh/nginx-luaCOPY ./nginx.conf /etc/nginx
COPY ./handler.lua /etc/nginx/
COPY ./env_var_echo.py /etc/nginx/RUN apk update
RUN apk add python3
RUN nginx -s reload

I run the image and then get in the docker:

docker run -it -d -p 8080:80 --name my-ngx-lua nginx-lua
docker exec -it my-ngx-lua sh

Then I define a new environment variable from inside the docker:

/etc/nginx # export SECRET=thisIsMySecret
/etc/nginx # echo $SECRET
thisIsMySecret
/etc/nginx #

EDIT: After defining the new env var, I exit the container and then get into it again and it is not there anymore:

/etc/nginx # exit
iy@MacBook-Pro ~ % docker exec -it my-ngx-lua sh
/etc/nginx # echo $SECRET/etc/nginx #

I run the python script and I expect to receive "thisIsMySecret", which is the value I defined.

import ossecret_key = os.environ.get('SECRET')
print(secret_key + '\n')

But I get None instead.

Only if I call any env var that already came with the docker (PATH for example), python will return the value of it. But if it is an env var that I just defined, it will return None.

BTW, I tried the same with lua and received nil. hence I am pretty sure the issue is from Alpine.

I am not looking for a solution like defining the env var from docker build.

Thanks.

This

After defining the new env var, I exit the container

is the cause. Exported variable only exists while the main process does and it is only visible to the process it was declared in.

What you need is to use the -e option when you start the container:

docker run -e SECRET=mysecret ...

With this docker will add the environment variable to the main process (NGINX in this case) and to docker exec commands as well.