docker-compose: the version does matter

I know, serious people use Kubernetes, but all I had was three small containers to deploy to run my website, all on the same host, and hence I figured docker-compose would do. So I set it all up, created my docker-compose.yml YAML file, tried to deploy it - only to discover that on the deployment host some of the tags would not work, one of them being target.

So I spent the next few hours digging into it and, it turns out, some version of docker-compose read in all the tags they can interpret, while others only interpret the ones allowed in the version specified in the first line of the file:

version: "3.7"

services:

  web:
    build:
      context: .
      target: "web"
    container_name: "web0"

  wproxy:
    build:
      context: .
      target: "wproxy"
    container_name: "wproxy0"
    ports:
      - "80:80"
    volumes:
      - letsencrypt_data:/etc/letsencrypt
    links:
      - web

  wproxy_s:
    build:
      context: .
      target: "wproxy_s"
    container_name: "wproxy_s0"
    ports:
      - "443:443"
    volumes:
      - letsencrypt_data:/etc/letsencrypt
      - html_home:/var/www/html
    links:
      - web

volumes:
  letsencrypt_data:
  html_home:

Initially my file read:

version: "3"

When I changed to to its current form:

version: "3.7"

The issue went away.

So yes, docker-compose is a useful orchestration tool, allowing to consistently and easily deploy small containerized applications. Only remember: version does matter, make sure you specify the correct one.

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