add healthcheck and depends_on

[qunabu]

wait for postgres to be fully working before launching main app docker image

example

services:
  db:
    image: postgres
    environment:
      - POSTGRES_USER=king
      - POSTGRES_DB=kong
      - POSTGRES_HOST_AUTH_METHOD=trust
    healthcheck:
      test: pg_isready -U postgres

  web:
    image: alpine
    depends_on: 
      db:
        condition: service_healthy

[qunabu]

https://docs.docker.com/compose/startup-order/

depends_on does not wait for db and redis to be “ready” before starting web - only until they have been started. If you need to wait for a service to be ready, see Controlling startup order for more on this problem and strategies for solving it.
The depends_on option is ignored when deploying a stack in swarm mode with a version 3 Compose file.