add volume to example app config, add module 9

08-running-containers/docker-compose.yml

@@ -42,7 +42,11 @@ services:
     restart: unless-stopped
   db:
     image: postgres:15.1-alpine
+    volumes:
+      - pgdata:/var/lib/postgresql/data
     environment:
       - POSTGRES_PASSWORD=foobarbaz
     ports:
       - 5432:5432
+volumes:
+  pgdata: