Add support for address_mode = "alloc"

[cneira]

@cneira Thanks for your update.

Now also can not support address_mode = "alloc"

cni conf: /etc/cni/conf.d/firecracker.conflist

{
  "name": "firecracker",
  "cniVersion": "0.4.0",
  "plugins": [
    {
      "type": "ptp",
      "ipMasq": true,
      "ipam": {
        "type": "host-local",
        "subnet": "192.168.60.0/24",
        "resolvConf": "/etc/resolv.conf"
      }
    },
    {
      "type": "tc-redirect-tap"
    }
  ]
}

job config

job "hello" {
    datacenters = ["dc1"]
    type = "service"

    group "sshd" {
        network {
            # mode = "cni/mynet"
            port "ssh" {
                to = 22
            }
        }
        service {
            name = "sshd"
            port = "ssh"
            address_mode = "alloc"
            check {
                type = "tcp"
                interval = "10s"
                timeout = "2s"
                address_mode = "alloc"
            }
        }

        task "sshd" {
            driver = "firecracker-task-driver"

            config {
                KernelImage = "/home/ox0spy/projects/nomad/study/firecracker/vmlinux.bin"
                BootDisk = "/home/ox0spy/projects/nomad/study/firecracker/rootfs.ext4"
                Firecracker = "/usr/local/bin/firecracker"
                Vcpus       = 1
                Mem         = 128
                Network     = "firecracker"
            }
        }
    }
}

docs for address_mode in service block: https://www.nomadproject.io/docs/job-specification/service#address_mode

run job

nomad status <alloc-id> got the below error message:

Setup Failure  failed to setup alloc: pre-run hook "group_services" failed: unable to get address for service "sshd": cannot use address_mode="alloc": no allocation network status reported

Originally posted by @ox0spy in https://github.com/cneira/firecracker-task-driver/issues/9#issuecomment-862496014

[zh4n7wm]

update more detail description.

add new capability

diff --git a/driver/driver.go b/driver/driver.go
index c5fc599..c7e65da 100644
--- a/driver/driver.go
+++ b/driver/driver.go
@@ -83,6 +83,7 @@ var (
                SendSignals: false,
                Exec:        false,
                FSIsolation: drivers.FSIsolationImage,
+               NetIsolationModes: []drivers.NetIsolationMode{drivers.NetIsolationModeGroup, drivers.NetIsolationModeTask},
        }
 )

add mode = "cni/firecracker" to network block, then did not report this error; but consul get the wrong ip address.

I think using address_mode = "alloc" and network -> mode = "cni/firecracker", nomad will assign the ip address for service, so firecracker-task-driver should use assigned ip address.

but, it seems that firecracker apply a new ip address: https://github.com/cneira/firecracker-task-driver/blob/master/driver/options.go#L165

containerd task driver use cfg.NetworkIsolation.Path for new container/allocation : https://github.com/Roblox/nomad-driver-containerd/blob/master/containerd/driver.go#L452