There are central network config files for Snappy, Server, Client, 
MaaS, cloud-init in /etc/netplan/*.yaml. All installers only generate 
such a file, no /etc/network/interfaces any more. There is also a 
netplan command line tool to drive some operations.

Systems are configured during early boot with a “network renderer” 
which reads /e/n/*.yaml and writes configuration to /run to hand off 
control of devices to the specified networking daemon. 

network:
  version: 2
  # if specified globally, can only realistically have that value, as networkd cannot
  # render wifi/3G. This would be shipped as a separate config.d/ by desktop images.
  # it can also be specified by-type or by-device
  #renderer: NetworkManager
  ethernets:
    # opaque ID for physical interfaces with match rules, only referred to by
    # other stanzas
    id0:
      match:
        macaddress: 00:11:22:33:44:55
      wakeonlan: true
      dhcp4: true
      addresses:
        - 192.168.14.2/24
        - 2001:1::1/64
    lom:
      # example for explicitly setting a backend (default would be networkd)
      renderer: network-manager
      match:
        driver: ixgbe
      # you are responsible for setting tight enough match rules
      # that only match one device if you use set-name
      set-name: lom1
      dhcp6: true
    switchports:
      # all cards on second PCI bus; unconfigured by themselves, will be added
      # to br0 below
      match:
        name: enp2*
      mtu: 1280
  wifis:
    all-wlans:
      # useful on a system where you know there is only ever going to be one device
      match: {}
      access-points:
        "Joe's home":
            # mode defaults to "managed" (client), key type to wpa-psk
            password: "s3kr1t"
    # this creates an AP on wlp1s0 using hostapd; no match rules, thus ID
    # is the interface name
    wlp1s0:
      access-points:
        "guest":
          mode: ap
          channel: 11
          # no WPA config implies default of open
  bridges:
    # renderer: NetworkManager    
    # the key name is the name for virtual (created) interfaces; 
    # no ‘match’ or ‘set-name’ attributes are allowed.
    br0:
      # IDs of the components; switchports expands into multiple interfaces
      interfaces: [wlp1s0, switchports]
      dhcp4: true
  routes:
   - to: 0.0.0.0/0
     via: 11.0.0.1
     metric: 3
  nameservers:
    search: [foo.local, bar.local]
    addresses: [8.8.8.8]