Run dependent Services before building Service Image

Docker Engine Compose
, ,
1 
version: "3.9"
services:
  postgres:
    image: postgres:15-alpine
    container_name: nettu_db
    volumes:
      - ./database/data:/var/lib/postgresql/data
    restart: on-failure
    env_file:
      - ./nettu_db.env

  app:
    build: ..
    ports:
      - "5000:5000"
    env_file:
      - ./nettu.env
    volumes:
      - ../:/var/application
    command: bash -c "cargo watch -x run"
    container_name: nettu
    init: true
    entrypoint:
      - "integrations/wait-for.sh"
      - "postgres:5432"
      - "--"
    depends_on:
      - postgres

I want the postgres service to run at the same time or before app builds & runs, because it depends on postgres the whole time, from the beginning.

How is that achievable with Docker tools?

2

I am not really sure I understand the question. You shouldn’t connect to a database in build time so when the images are built are usually not important only when the services start and in what order. If you have a special case which I can’t imagine now and you need to connect to a database during build, you need to implement a “wait” function which tries to connect to the DB in a loop until it succeeds and continues with the “main” process after that.

If you want postgres to run before the app runs, the solution is similar. depends_on can make sure the container starts before another container, but starting a container doesn’t mean a process inside the container is ready. If you have healthchecks, you can also try the long syntax of depends_on

and start a service when another service is considered healthy.