$ cat Dockerfile.postgres
FROM postgres:12
EXPOSE 5432
$ cat docker-compose.yml
version: '3.1'
services:
  app:
    image: postgres
    depends_on:
      - postgresqldb
    environment:
      - POSTGRES_PASSWORD=some
  postgresqldb:
    image: postgres
    build:
      context: ./
      dockerfile: Dockerfile.postgres
    ports:
      - "5432:5432"
    environment:
      - PGDATA=/var/lib/postgresql/data
      - POSTGRES_PASSWORD=111111
      - POSTGRES_USER=usrdb
$ docker-compose up -d
Creating network "2_default" with the default driver
Creating 2_postgresqldb_1 ... done
Creating 2_app_1          ... done
$ docker-compose exec -- app /bin/bash
root@d986742c83bd:/# PGPASSWORD=111111 psql -U usrdb -d usrdb -h postgresqldb
psql (12.9 (Debian 12.9-1.pgdg110+1))
Type "help" for help.

usrdb=#