investigate support for init container

[compose-spec]

investigate support for init container

[acran]

To throw in just another idea (based on the example from @hangyan above):

version: "3"
services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
    depends_on:
      init_container:
        condition: service_finished_successfully
  init_container:
      image: busybox
      command:  ping www.google.com
  db:
    image: postgres

I.e. introduce a new enum value (service_finished_successfully) to the depends_on condition such that the dependent service will only start after the other service exited with a successful exit code - or just exited at all (service_finished).
See https://docs.docker.com/compose/compose-file/compose-file-v2/#depends_on and #72

[EricHripko]

I like the suggestion from @acran 👍 It seems like a natural extension of Compose language.

[hangyan]

version: "3"
services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
    init_container:
      image: busybox
      command:  ping www.google.com
  db:
    image: postgres

Some rough thoughts

[mikesir87]

I actually just came across this use case, but I'll admit my first approach/thought was to do it as outlined by @acran. The depends_on already supports some of part of this use case, so adding another enum value makes sense. It also aligns with how ECS thought about it (can't deep-link onto the page, but see the dependsOn section in their task definition parameters).