Lab #9: ENV instruction

The ENV instruction in Dockerfile sets the environment variable for your container when you start. The default value can be overridden by passing --env <key>=<value> when you start the container.


Tested Infrastructure

Platform Number of Instance Reading Time
Play with Docker 1 5 min



Writing a Dockerfile with ENV instruction


FROM alpine:3.9.3
LABEL maintainer="Collabnix"

ENV WELCOME_MESSAGE="Welcome to Docker World"

CMD ["sh", "-c", "echo $WELCOME_MESSAGE"]

Building Docker Image

$ docker build -t env:v1 .

Running container env:v1

$ docker container run env:v1
Welcome to Docker World

Override existing env while running container

$ docker container run --env WELCOME_MESSAGE="Welcome to Docker Workshop" env:v1 
Welcome to Docker Workshop


Savio Mathew

Lab #10: VOLUME instruction