Fetching IP addresses for vagrant-hostmanager from libvirt

To fetch the IP address from the interface other than eth0 for
vagrant-hostmanager plugin, it must be fetched from the DHCP
leases from libvirt network. The previously used one-liner,
which was using virsh with awk, returns multiple addresses
when VM was destroyed before expiration of its DHCP lease.

This script solved this problem by getting only the newest
DHCP lease and gives a possibility to destroy Vagrant
environment and set up again without worrying about hosts
resolving.

Co-Authored-By: Michal Rostecki <mrostecki@mirantis.com>
Partially-Implements: blueprint vagrant
Related-Id: Ic469b46f4d02d873c27114cbd268b86521eef32b
Related-Id: I81f07b7e4a202af68fd3cf9fdb308c3734c40a83

Change-Id: I408415e95483c1b8988d0f67c654212de63bece2

dev/vagrant/Vagrantfile

@@ -141,7 +141,7 @@ Vagrant.configure(2) do |config|
     case PROVIDER
     when "libvirt"
       if vm.name
-        `virsh -c qemu:///system net-dhcp-leases vagrant-private-dhcp | awk -F'[ /]+' '/#{vm.name} / {print $6}'`.chop
+        `python newest_dhcp_lease.py #{vm.name}`.chop
       end
     when "virtualbox_ubuntu"
     when "virtualbox_centos"

dev/vagrant/newest_dhcp_lease.py

@@ -0,0 +1,131 @@
+#!/usr/bin/env python
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Command-line utility to get the IP address from the newest DHCP lease.
+
+It's written for using with vagrant-hostmanager and vagrant-libvirt plugins.
+Vagrant-hostmanager by default fetches only IP addresses from eth0 interfaces
+on VM-s. Therefore, the first purpose of this utility is to be able to fetch
+the address also from the other interfaces.
+
+Libvirt/virsh only lists all DHCP leases for the given network with timestamps.
+DHCP leases have their expiration time, but are not cleaned up after destroying
+VM. If someone destroys and sets up the VM with the same hostname, we have
+many DHCP leases for the same hostname and we have to look up for timestamp.
+That's the second purpose of this script.
+"""
+
+import argparse
+import csv
+import functools
+import operator
+import xml.etree.ElementTree as etree
+
+import libvirt
+
+
+class NoBridgeInterfaceException(Exception):
+    pass
+
+
+class NoDHCPLeaseException(Exception):
+    pass
+
+
+def libvirt_conn(f):
+    @functools.wraps(f)
+    def wrapper(*args, **kwargs):
+        conn = libvirt.openReadOnly('qemu:///system')
+        return f(conn, *args, **kwargs)
+    return wrapper
+
+
+@libvirt_conn
+def get_vir_network_dhcp_lease(conn, vm_name):
+    """Libvirt since 1.2.6 version provides DHCPLeases method in virNetwork.
+
+    That's the current official way for getting DHCP leases and this
+    information isn't stored anywhere else anymore.
+    """
+    network = conn.networkLookupByName('vagrant-private-dhcp')
+    dhcp_leases = libvirt.virNetwork.DHCPLeases(network)
+
+    vm_dhcp_leases = filter(lambda lease: lease['hostname'] == vm_name,
+                            dhcp_leases)
+
+    newest_vm_dhcp_lease = sorted(vm_dhcp_leases,
+                                  key=operator.itemgetter('expirytime'),
+                                  reverse=True)[0]['ipaddr']
+    return newest_vm_dhcp_lease
+
+
+def get_mac_address(conn, domain_name):
+    """Get MAC address from domain XML."""
+    domain = conn.lookupByName(domain_name)
+    domain_xml = domain.XMLDesc()
+    domain_tree = etree.fromstring(domain_xml)
+    devices = domain_tree.find('devices')
+    interfaces = devices.iterfind('interface')
+
+    for interface in interfaces:
+        interface_type = interface.get('type')
+        if interface_type != 'bridge':
+            continue
+        mac_element = interface.find('mac')
+        mac_address = mac_element.get('address')
+        return mac_address
+
+    raise NoBridgeInterfaceException()
+
+
+@libvirt_conn
+def get_dnsmasq_dhcp_lease(conn, vm_name):
+    """In libvirt under 1.2.6 DHCP leases are stored in file.
+
+    There is no API for DHCP leases yet.
+    """
+    domain_name = 'vagrant_' + vm_name
+    mac_address = get_mac_address(conn, domain_name)
+
+    with open(
+        '/var/lib/libvirt/dnsmasq/vagrant-private-dhcp.leases'
+    ) as leases_file:
+        reader = csv.reader(leases_file, delimiter=' ')
+        for row in reader:
+            lease_mac, lease_ip, lease_vm_name = row[1:4]
+            if not (lease_mac == mac_address and lease_vm_name == vm_name):
+                continue
+            return lease_ip
+
+    raise NoDHCPLeaseException()
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('vm_name', help='Name of the virtual machine')
+
+    args = parser.parse_args()
+    vm_name = args.vm_name
+
+    if libvirt.getVersion() >= 1002006:
+        newest_dhcp_lease = get_vir_network_dhcp_lease(vm_name)
+    else:
+        newest_dhcp_lease = get_dnsmasq_dhcp_lease(vm_name)
+
+    print(newest_dhcp_lease)
+
+
+if __name__ == '__main__':
+    main()