Docker compose Postgres ready to operate

docker-compose.yml

version: '2.1'

services:
  postgresql:
    image: postgres:11-alpine
    restart: always
    ports:
    - 5432:5432
    environment:
      POSTGRES_DB: db
      POSTGRES_USER: usr
      POSTGRES_PASSWORD: psw
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 2s
      timeout: 2s
      retries: 10
  # only needed to wait postgresql to up
  nop:
    image: alpine:3.11
    depends_on:
      postgresql:
        condition: service_healthy