Lab #9: Create an image with 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.

Pre-requisite:

Tested Infrastructure

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

Pre-requisite

  • Create an account with DockerHub
  • Open PWD Platform on your browser
  • Click on Add New Instance on the left side of the screen to bring up Alpine OS instance on the right side

Assignment

  • Writing a Dockerfile with ENV instruction
  • Building Docker Image
  • Running container env:v1
  • Override existing env while running container

Writing a Dockerfile with ENV instruction

Dockerfile

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

Next » Create an image with VOLUME instruction