docker service create --name postgresql
  --mount src=pg_data,dst=/var/lib/postgresql/data/pgdata
  -p 6542:5432
  -e POSTGRES_USER="user"
  -e POSTGRES_DB="db"
  -e POSTGRES_PASSWORD="pass"
  -e PGDATA=/var/lib/postgresql/data/pgdata
  --constraint 'node.role == manager'
  postgres

docker volume create pg_data

docker network create -d overlay mynet

docker service create --name postgresql
  --mount ...
  --network mynet
  postgres

docker service create --name myjavaapp
  --network mynet
  myjavaapp

jdbc:postgresql://postgresql:5432/db