Add support for external DNS/Static IPs, as well as bridged adapters other than virbr0

[ocient-cliimatta]

Many networks have external IPAM and/or DHCP servers to hand out IP addresses for VMs.

It would be great if a non-libvirt managed DHCP server could be used with Nomad's Virt driver.

Ideally, Nomad could use the builtin capability for qemu-agent to execute and return information from the guest's network adapters.

This method would enable almost universal support for different network configurations, like static IPs retrieved from an IPAM solution like Netbox/Infoblox, and enable bridged adapters other than the libvirt managed virbr0.

It would require qemu-guest-agent package to be installed inside the guest VM.

Example:
virsh qemu-agent-command virt-task-4930bb25 '{"execute":"guest-network-get-interfaces"}' | jq .

This returns JSON which could be parsed by Nomad:

{
  "return": [
    {
      "name": "lo",
      "ip-addresses": [
        {
          "ip-address-type": "ipv4",
          "ip-address": "127.0.0.1",
          "prefix": 8
        },
        {
          "ip-address-type": "ipv6",
          "ip-address": "::1",
          "prefix": 128
        }
      ],
      "statistics": {
        "tx-packets": 1875360,
        "tx-errs": 0,
        "rx-bytes": 133160856,
        "rx-dropped": 0,
        "rx-packets": 1875360,
        "rx-errs": 0,
        "tx-bytes": 133160856,
        "tx-dropped": 0
      },
      "hardware-address": "00:00:00:00:00:00"
    },
    {
      "name": "enp0s5",
      "ip-addresses": [
        {
          "ip-address-type": "ipv4",
          "ip-address": "10.14.30.29",
          "prefix": 24
        },
        {
          "ip-address-type": "ipv6",
          "ip-address": "redacted",
          "prefix": 64
        }
      ],
      "statistics": {
        "tx-packets": 958693,
        "tx-errs": 0,
        "rx-bytes": 439869753,
        "rx-dropped": 176893,
        "rx-packets": 1563633,
        "rx-errs": 0,
        "tx-bytes": 80836052,
        "tx-dropped": 0
      },
      "hardware-address": "redacted"
    }
  ]
}