Declaring variables in docker-compose

Question

I want to let my application know which image version it is running on.

The idea was to pass the Docker image tag into the image as an environment variable. However I don't want to change the version number in both the image line AND in the ENV variable line all the time.

Example:

version: "3"

VERSION=0.2.3

services:
  app:
    image: myimage:$VERSION
    environment:        
       - APPLICATION_VERSION:$VERSION

Is it possible to declare variables in order to update all values together or is there any other solution available?

Answer 1

You cannot define $VERSION inside the docker-compose.yml.

You have two options for this:

• define it in a .env file
• send as a command line argument when you run the docker-compose command. e.g. VERSION=0.2.3 docker-compose up -d