[WIP] Allow to specify dns forwarders

lago/prefix.py

@@ -390,10 +390,11 @@ def _add_dns_records(self, conf, mgmts):
         LOGGER.debug('Using network %s as main DNS server', dns_mgmt)
         forward = conf['nets'][dns_mgmt].get('gw')
         dns_records = {}
+
         for net_name, net_spec in nets.iteritems():
             dns_records.update(net_spec['mapping'].copy())
             if net_name not in mgmts:
-                net_spec['dns_forward'] = forward
+                net_spec['dns_forwarders'] = [{'addr': forward}]
 
         for mgmt in mgmts:
             if nets[mgmt].get('dns_records'):

lago/providers/libvirt/network.py

@@ -20,6 +20,7 @@
 from future.builtins import super
 from collections import defaultdict
 import functools
+import itertools
 import logging
 import time
 from copy import deepcopy
@@ -52,6 +53,10 @@ def name(self):
     def gw(self):
         return self._spec.get('gw')
 
+    @property
+    def subnet(self):
+        return self.gw().split('.')[2]
+
     def mtu(self):
         if self.libvirt_con.getLibVersion() > 3001001:
             return self._spec.get('mtu', '1500')
@@ -145,50 +150,189 @@ def spec(self):
         return deepcopy(self._spec)
 
 
-class NATNetwork(Network):
-    def _generate_dns_forward(self, forward_ip):
-        dns = ET.Element('dns', forwardPlainNames='yes')
-        dns.append(ET.Element('forwarder', addr=forward_ip))
-        return dns
+class LibvirtDNS(object):
+    """
+    This class represents the `dns` element in Libvirt's
+    Network XML.
+
+    This class has convenient "class methods" for generating
+    specific dns elements.
+
+    For more information please refer to Libvirt's documentation:
+    https://libvirt.org/formatnetwork.html
+
+    Attributes:
+        _dns(lxml.etree.Element): The root of the `dns` element
+    """
+
+    def __init__(self, enable=True, forward_plain_names=True):
+        """
+        Args:
+            enabled(bool): If false, don't create a dns server
+            forward_plain_names(bool): If false, names that are not FQDNs
+                will not be forwarded to the host's upstream server.
+        """
+        forward_plain_name = 'yes' if forward_plain_names else 'no'
+
+        if enable:
+            self._dns = ET.Element(
+                'dns',
+                enable='yes',
+                forwardPlainNames=forward_plain_name,
+            )
+        else:
+            self._dns = ET.Element('dns', enable='no')
+
+    @classmethod
+    def generate_dns_forward(cls, forwarders):
+        """
+        Generate a dns server that forwards request to one or more dns servers.
+
+        Args:
+            forwarders(list of dicts): Each dict represents a `forwarder`
+                that will be added to the dns server. The dict's items
+                will be added as attributes to the forwarder element.
+        """
+        dns = cls()
+        dns.add_forwarders(*forwarders)
+
+        return dns.get_xml_object()
 
-    def _generate_dns_disable(self):
-        dns = ET.Element('dns', enable='no')
-        return dns
+    @classmethod
+    def generate_dns_disable(cls):
+        """
+        Generate a disbaled dns server.
+        """
+        dns = cls(enable=False)
+
+        return dns.get_xml_object()
+
+    @classmethod
+    def generate_default_dns(cls):
+        """
+        Generate a default dns server.
+        Please refer to the default values of the `__init__` method
+        in order to see the properties of a default dns server.
+        """
+        return cls().get_xml_object()
+
+    @classmethod
+    def generate_main_dns(cls, records, forwarders, forward_plain_names):
+        """
+        Generate a dns server for Lago's management network.
+
+        Args:
+            records(list of tuples): For a tuple "t", t[0] is a hostname
+                and t[1] is its IP. Each tuple will be added as a `host`
+                element to the dns server.
+            forwarders(list of dicts): List of forwarders that will be added
+                ths dns server.
+            forward_plain_name(bool): If false, names that are not
+                FQDNs will not be forwarded to the host's upstream server.
+        """
+        dns = cls(forward_plain_names=forward_plain_names)
 
-    def _generate_main_dns(self, records, subnet, forward_plain='no'):
-        dns = ET.Element('dns', forwardPlainNames=forward_plain)
         reverse_records = defaultdict(list)
-        ipv6_prefix = self._ipv6_prefix(subnet=subnet)
-        for hostname, ip in records.iteritems():
+        for hostname, ip in records:
             reverse_records[ip] = reverse_records[ip] + [hostname]
+
         for ip, hostnames in reverse_records.iteritems():
-            record_ipv4 = ET.Element('host', ip=ip)
-            record_ipv6 = ET.Element('host', ip=ipv6_prefix + ip)
-            for hostname in sorted(hostnames):
-                host = ET.Element('hostname')
-                host.text = hostname
-                record_ipv4.append(host)
-                record_ipv6.append(deepcopy(host))
-            dns.append(record_ipv4)
-            dns.append(record_ipv6)
-
-        return dns
+            dns.add_host(ip, *hostnames)
+
+        dns.add_forwarders(*forwarders)
+
+        return dns.get_xml_object()
+
+    def add_forwarders(self, *forwarders):
+        """
+        Add `forwarder(s)` to the dns server.
+
+        Args:
+            forwarders(dicts): One or more dicts that represents a forwader.
+                Each item in the dict will be mapped to an attribute of
+                the forwarder.
+        """
+        for forwarder in forwarders:
+            self._dns.append(ET.Element('forwarder', **forwarder))
 
+    def add_host(self, ip, *hostnames):
+        """
+        Add `host entry(s)` to the dns server.
+
+        Args:
+            ip(str): The host's IP address.
+            hostnames(str): One or more hostnames that will be mapped to `ip`.
+        """
+        host_element = ET.Element('host', ip=ip)
+
+        for hostname in sorted(hostnames):
+            hostname_element = ET.Element('hostname')
+            hostname_element.text = hostname
+            host_element.append(hostname_element)
+
+        self._dns.append(host_element)
+
+    def get_xml_object(self):
+        """
+        Returns:
+            (lxml.etree.Element): The dns server
+        """
+        return deepcopy(self._dns)
+
+
+class NATNetwork(Network):
     def _ipv6_prefix(self, subnet, const='fd8f:1391:3a82:'):
         return '{0}{1}::'.format(const, subnet)
 
+    def get_ipv6_dns_records(self, mapping):
+        """
+        Given a mapping between host names and an IPv4 addresses,
+        return a new mapping from hostnames and their IPv6.
+        The IPv6 address is gernerate from the host's IPv4.
+
+        Args:
+            mapping(dict): A mapping between host names and their
+                IPv4 addresses.
+
+        Returns:
+            (dict): A mapping between host names and their IPv6 addresses.
+        """
+        return {
+            hostname: self.ipv6_prefix + ip
+            for hostname, ip in mapping.items()
+        }
+
+    def get_ipv4_and_ipv6_dns_records(self, mapping_name):
+        """
+        Get a chain of tuples that represent a mapping between a hostname
+        and its IP address. The chain will include tuples for IPv4 and IPv6
+        addresses.
+
+        Args:
+            mapping_name(str): From which dict of this network spec the chain
+                should be built.
+
+        Returns:
+            (itertools.chain): A chain of tuples.
+        """
+        return itertools.chain(
+            self.spec[mapping_name].iteritems(),
+            self.get_ipv6_dns_records(self.spec[mapping_name]).iteritems(),
+        )
+
+    @property
+    def ipv6_prefix(self):
+        return self._ipv6_prefix(self.subnet)
+
     def _libvirt_xml(self):
         net_raw_xml = libvirt_utils.get_template('net_nat_template.xml')
-
-        subnet = self.gw().split('.')[2]
-        ipv6_prefix = self._ipv6_prefix(subnet=subnet)
         mtu = self.mtu()
 
         replacements = {
             '@NAME@': self._libvirt_name(),
             '@BR_NAME@': ('%s-nic' % self._libvirt_name())[:12],
             '@GW_ADDR@': self.gw(),
-            '@SUBNET@': subnet
+            '@SUBNET@': self.subnet
         }
         for k, v in replacements.items():
             net_raw_xml = net_raw_xml.replace(k, v, 1)
@@ -223,8 +367,10 @@ def make_ipv4(last):
             dhcpv6.append(
                 ET.Element(
                     'range',
-                    start=ipv6_prefix + make_ipv4(self._spec['dhcp']['start']),
-                    end=ipv6_prefix + make_ipv4(self._spec['dhcp']['end']),
+                    start=self.ipv6_prefix +
+                    make_ipv4(self._spec['dhcp']['start']),
+                    end=self.ipv6_prefix +
+                    make_ipv4(self._spec['dhcp']['end']),
                 )
             )
 
@@ -247,7 +393,7 @@ def make_ipv4(last):
                     ET.Element(
                         'host',
                         id='0:3:0:1:' + utils.ipv4_to_mac(ip4),
-                        ip=ipv6_prefix + ip4,
+                        ip=self.ipv6_prefix + ip4,
                         name=hostname
                     )
                 )
@@ -260,16 +406,23 @@ def make_ipv4(last):
                     localOnly='yes'
                 )
                 net_xml.append(domain_xml)
+
                 net_xml.append(
-                    self._generate_main_dns(self._spec['dns_records'], subnet)
+                    LibvirtDNS.generate_main_dns(
+                        self.get_ipv4_and_ipv6_dns_records('dns_records'),
+                        self._spec.get('dns_forwarders', []),
+                        forward_plain_names=False
+                    )
                 )
             else:
                 if self.libvirt_con.getLibVersion() < 2002000:
                     net_xml.append(
-                        self._generate_dns_forward(self._spec['dns_forward'])
+                        LibvirtDNS.generate_dns_forward(
+                            self._spec['dns_forwarders']
+                        )
                     )
                 else:
-                    net_xml.append(self._generate_dns_disable())
+                    net_xml.append(LibvirtDNS.generate_dns_disable())
         else:
             LOGGER.debug(
                 'Generating network XML with compatibility prior to %s',
@@ -286,14 +439,15 @@ def make_ipv4(last):
                     )
                     net_xml.append(domain_xml)
 
-                net_xml.append(
-                    self._generate_main_dns(
-                        self._spec['mapping'], subnet, forward_plain='yes'
-                    )
+                dns_element = LibvirtDNS.generate_main_dns(
+                    self.get_ipv4_and_ipv6_dns_records('mapping'),
+                    [],
+                    forward_plain_names=True,
                 )
+
+                net_xml.append(dns_element)
             else:
-                dns = ET.Element('dns', forwardPlainNames='yes', enable='yes')
-                net_xml.append(dns)
+                net_xml.append(LibvirtDNS.generate_default_dns())
 
         LOGGER.debug(
             'Generated Network XML\n {0}'.format(

tests/unit/lago/providers/libvirt/test_dns.py

@@ -0,0 +1,77 @@
+#
+# Copyright 2017 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+#
+# Refer to the README and COPYING files for full details of the license
+#
+import lxml.etree as ET
+from xmlunittest import XmlTestCase
+
+from lago.providers.libvirt.network import LibvirtDNS
+
+
+class TestDNS(XmlTestCase):
+    def test_dns_disable(self):
+        _xml = '<dns enable="no" />'
+        dns = LibvirtDNS.generate_dns_disable()
+
+        self.assertXmlEquivalentOutputs(ET.tostring(dns), _xml)
+
+    def test_default_dns(self):
+        _xml = '<dns enable="yes" forwardPlainNames="yes" />'
+        dns = LibvirtDNS.generate_default_dns()
+
+        self.assertXmlEquivalentOutputs(ET.tostring(dns), _xml)
+
+    def test_forward_dns(self):
+        _xml = """
+        <dns enable="yes" forwardPlainNames="yes">
+            <forwarder addr="8.8.8.8" />
+        </dns>
+        """
+
+        dns = LibvirtDNS.generate_dns_forward([{'addr': '8.8.8.8'}])
+
+        self.assertXmlEquivalentOutputs(ET.tostring(dns), _xml)
+
+    def test_main_dns(self):
+        _xml = """
+        <dns enable="yes" forwardPlainNames="yes">
+            <host ip="192.168.122.2">
+                <hostname>myhost</hostname>
+                <hostname>myhostalias</hostname>
+            </host>
+            <forwarder addr="8.8.8.8" />
+            <forwarder addr="8.8.4.4" domain="example.com" />
+        </dns>
+        """
+
+        records = [
+            ('myhost', '192.168.122.2'), ('myhostalias', '192.168.122.2')
+        ]
+
+        forwarders = [
+            {
+                'addr': '8.8.8.8'
+            }, {
+                'addr': '8.8.4.4',
+                'domain': 'example.com'
+            }
+        ]
+
+        dns = LibvirtDNS.generate_main_dns(records, forwarders, True)
+
+        self.assertXmlEquivalentOutputs(ET.tostring(dns), _xml)