instruction: Create a Dockerfile for networking
output: ```dockerfile
  from the db service, because they do not share a network in common. Only app can talk to both.
  
  services:
   proxy:
   build: ./proxy
   networks:
   - frontend
   app:
   build: ./app
   networks:
   - frontend
   - backend
   db:
   image: postgres
   networks:
   - backend
  
  networks:
   frontend:
   # Specify driver options
   driver: bridge
   driver_opts:
   com.docker.network.bridge.host_binding_ipv4: "127.0.0.1"
   backend:
   # Use a custom driver
   driver: custom-driverNetworks can be configured with static IP addresses by setting the
  ipv4_address and/or ipv6_address for each attached network.Networks can also be given a
  custom name:
  
  services:
   # ...
  networks:
   frontend:
   name: custom_frontend
   driver: custom-driver-1Configure the default networkInstead of, or as well as, specifying your own networks, you can also change the settings of the app-wide default network by defining an entry under networks named default:
  
  services:
   web:
   build: .
   ports:
   - "8000:8000"
   db:
   image: postgres
  
  networks:
   default:
   # Use a custom driver
   driver: custom-driver-1Use an existing networkIf you've manually created a bridge network outside of Compose using the docker network create command, you can connect your Compose services to it by marking the network as external.If you want your containers to join a pre-existing network, use the
  external option
  
  services:
   # ...
  networks:
   network1:
   name: my-pre-existing-network
   external: trueInstead of attempting to create a network called [projectname]_default, Compose looks for a network called my-pre-existing-network and connects your app's containers to it.Further reference informationFor full details of the network configuration options available, see the following references:Top-level networks elementService-level networks attribute
  Request changesTable of contentsUpdate containers on the networkLink containersMulti-host networkingSpecify custom networksConfigure the default networkUse an existing networkFurther reference information
  
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