proxmox-cloudbase_init

Here is an example of the format that proxmox generates.
Proxmox generates a cd / dvd drive named config-2 with the following files:

/OPENSTACK/CONTENT/0000      #network config
/OPENSTACK/LATEST/META_DATA.JSON   #link to network config
/OPENSTACK/LATEST/USER_DATA    #hostname, new user,etc


----content file 0000----
auto lo
iface lo inet loopback

        dns_nameservers 8.8.8.8
auto eth0
iface eth0 inet dhcp

----content file META_DATA.JSON----
{
     "uuid": "b05c9c5f540dc5ef8b8e3adb1eb3f29fc9193a8d",
     "network_config": { "content_path": "/content/0000" }
}

----content file USER_DATA----
#cloud-config
hostname: testPBS
manage_etc_hosts: true
user: usertest
password: $5$lXJ79pFq$PYISfu4s3SpK6PpPGoH7U8fHOfPuXYAVsBayAgCkfe5
chpasswd:
  expire: False
users:
  - default
package_upgrade: true