3. Environment Variables

Environment Variables

Part 1: Building the image

This container will run a simple Python webserver built on the flask framework. This uses the image from Docker Hub python:3-alpine3.10.

docker build --rm -t 311tutorial:envvars .

Part 2: Changing the variable

This webserver will display the value of the env var MYVAR. An envvar is not attached to a specific programing language. Many languages have a way to get and set them. In this case, it is Python, but Java, JS, Golang etc... all have his ability. The container built has an env var MYVAR that is set to the string default as defined in the Dockerfile. This can be changed when creating an instance of the container (when running it) with the -e flag. Like so:

docker run --rm -it -p 42069:80 -e MYVAR="docker is great" 311tutorial:envvars

Now, go to http://localhost:42069 on your web browser to see the webpage!

Try setting MYVAR to something else too, remember, you don't have to rebuild the container, only rerun!