Docker Compose 3 multiline

Question

Why this is not working on docker compose version 3?

nginx:
   image: nginx
   container_name: nginx
   environment:
       VIRTUAL_HOST: > 
       proj1.local,proj2.local,
       proj3.local,proj4.local,proj5.local

I've a lot of virtual hosts and I need to go multilne but I receive:

ERROR: yaml.scanner.ScannerError: while scanning a simple key
  in "./docker-compose.yml", line 31, column 7
could not find expected ':'
  in "./docker-compose.yml", line 32, column 7

What am I doing wrong?

Answer 1

Tools such as Yamllint are your friend when seeing those types of errors. That said, it sometimes doesn't give you a meaningful error when failing validation.

What you have in the example is an indentation problem. You should be using:

nginx:
  image: nginx
  container_name: nginx
  environment:
    VIRTUAL_HOST: > 
      proj1.local,proj2.local,
      proj3.local,proj4.local,proj5.local

Which will translate into:

nginx: 
  container_name: nginx
  environment: 
    VIRTUAL_HOST: "proj1.local,proj2.local, proj3.local,proj4.local,proj5.local"
  image: nginx