Don't use named volumes.

docker-compose.yml

@@ -40,13 +40,10 @@ services:
     env_file: db.env
     image: postgres:alpine
     volumes:
-      - db:/var/lib/postgresql/data
+      - /opaque_database:/var/lib/postgresql/data
   redis:
     deploy:
       placement:
         constraints:
           - node.role == manager
     image: redis:alpine
-
-volumes:
-  db: