User-provided environment variable within docker CMD

Question

I have successfully pushed my docker image to the swisscom app cloud (similar to this example: https://ict.swisscom.ch/2016/05/docker-and-cloudfoundry/).

Now I would like to use a user-provided environment variable within my docker CMD. Something like this:

ADD target/app.jar app.jar
CMD java -jar app.jar -S $USER_PROVIDED_ENV_VARIABLE

I also tried system-provided environment variables:

ADD target/app.jar app.jar
CMD java -jar app.jar -S $VCAP_APPLICATION

What am I doing wrong here?

Answer 1

If your Dockerfile is built like that, you'll simply need to pass the -e flag when running the image.

Example Dockerfile:

FROM ubuntu:16.10
ENV MY_VAR "default value" # Optional - set a default value.
CMD echo $MY_VAR

Build the image:

docker build -t my_image .

Run a container from the image:

docker run -e MY_VAR="my value here" my_image