# 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.
"""Multicast DNS implementation for API discovery.
This implementation follows RFC 6763 as clarified by the API SIG guideline
https://review.opendev.org/651222.
"""
import ipaddress
import logging
import time
from oslo_config import cfg
from oslo_config import types as cfg_types
import zeroconf
from ironic_python_agent import errors
from ironic_python_agent import utils
opts = [
cfg.BoolOpt('use_mdns',
default=utils.get_agent_params().get('ipa-use-mdns', False),
help='Whether to allow discovering the Ironic API URL via '
'multicast DNS (mDNS) when neither "ipa-api-url" nor '
'"ipa-inspection-callback-url" is set at all. mDNS '
'responses are not authenticated, so enabling this '
'option means any host able to answer this multicast '
'query on the local network can control where the '
'agent sends API requests and inspection data, and '
'can override other configuration options. Only '
'enable this if the deployment network is trusted. '
'Can be supplied as the "ipa-use-mdns" kernel '
'parameter. Explicitly setting "ipa-api-url" or '
'"ipa-inspection-callback-url" to "mdns" enables mDNS '
'discovery regardless of this option, since doing so '
'requires the same level of access.'),
cfg.ListOpt('allowed_overrides',
default=['inspection_callback_url', 'ntp_server'],
help='List of configuration option names (without the '
'"ipa_" prefix used in mDNS TXT records) that are '
'allowed to be overridden via mDNS. The default '
'restricts overrides to the minimum needed for a '
'bare environment (e.g. booting from a USB drive '
'with no local configuration). The API endpoint '
'and inspection callback URL are provided by the '
'mDNS service record itself and do not need to be '
'listed here. Set to an empty list to block all '
'TXT record overrides. mDNS responses are not '
'authenticated, so any host able to answer an '
'mDNS query on the local network can supply '
'these overrides. Living in the "mdns" group, '
'this option cannot itself be changed via mDNS.'),
cfg.IntOpt('lookup_attempts',
min=1, default=3,
help='Number of attempts to lookup a service.'),
cfg.Opt('params',
# This is required for values that contain commas.
type=cfg_types.Dict(cfg_types.String(quotes=True)),
default={},
help='Additional parameters to pass for the registered '
'service.'),
cfg.ListOpt('interfaces',
help='List of IP addresses of interfaces to use for mDNS. '
'Defaults to all interfaces on the system.'),
]
CONF = cfg.CONF
opt_group = cfg.OptGroup(name='mdns', title='Options for multicast DNS client')
CONF.register_group(opt_group)
CONF.register_opts(opts, opt_group)
LOG = logging.getLogger(__name__)
_MDNS_DOMAIN = '_openstack._tcp.local.'
[docs]
class Zeroconf(object):
"""Multicast DNS implementation client and server.
Uses threading internally, so there is no start method. It starts
automatically on creation.
.. warning::
The underlying library does not yet support IPv6.
"""
def __init__(self):
"""Initialize and start the mDNS server."""
interfaces = (CONF.mdns.interfaces if CONF.mdns.interfaces
else zeroconf.InterfaceChoice.All)
# If interfaces are set, let zeroconf auto-detect the version
ip_version = None if CONF.mdns.interfaces else zeroconf.IPVersion.All
self._zc = zeroconf.Zeroconf(interfaces=interfaces,
ip_version=ip_version)
self._registered = []
[docs]
def get_endpoint(self, service_type, skip_loopback=True,
skip_link_local=False):
"""Get an endpoint and its properties from mDNS.
If the requested endpoint is already in the built-in server cache, and
its TTL is not exceeded, the cached value is returned.
:param service_type: OpenStack service type.
:param skip_loopback: Whether to ignore loopback addresses.
:param skip_link_local: Whether to ignore link local V6 addresses.
:returns: tuple (endpoint URL, properties as a dict).
:raises: :exc:`.ServiceLookupFailure` if the service cannot be found.
"""
delay = 0.1
for attempt in range(CONF.mdns.lookup_attempts):
name = '%s.%s' % (service_type, _MDNS_DOMAIN)
info = self._zc.get_service_info(name, name)
if info is not None:
break
elif attempt == CONF.mdns.lookup_attempts - 1:
raise errors.ServiceLookupFailure(service=service_type)
else:
time.sleep(delay)
delay *= 2
all_addr = info.parsed_addresses()
# Try to find the first routable address
fallback = None
for addr in all_addr:
try:
loopback = ipaddress.ip_address(addr).is_loopback
except ValueError:
LOG.debug('Skipping invalid IP address %s', addr)
continue
else:
if loopback and skip_loopback:
LOG.debug('Skipping loopback IP address %s', addr)
continue
if utils.get_route_source(addr, skip_link_local):
address = addr
break
elif fallback is None:
fallback = addr
else:
if fallback is None:
raise errors.ServiceLookupFailure(
f'None of addresses {all_addr} for service %('
'{service_type} are valid')
else:
LOG.warning('None of addresses %s seem routable, '
'using %s', all_addr, fallback)
address = fallback
properties = {}
for key, value in info.properties.items():
try:
if isinstance(key, bytes):
key = key.decode('utf-8')
except UnicodeError as exc:
raise errors.ServiceLookupFailure(
f'Invalid properties for service {service_type}. Cannot '
f'decode key {key!r}: {exc!r}')
try:
if isinstance(value, bytes):
value = value.decode('utf-8')
except UnicodeError as exc:
LOG.debug('Cannot convert value %(value)r for key %(key)s '
'to string, assuming binary: %(exc)s',
{'key': key, 'value': value, 'exc': exc})
properties[key] = value
path = properties.pop('path', '')
protocol = properties.pop('protocol', None)
if not protocol:
if info.port == 80:
protocol = 'http'
else:
protocol = 'https'
if info.server.endswith('.local.'):
# Local hostname means that the catalog lists an IP address,
# so use it
host = address
if int(ipaddress.ip_address(host).version) == 6:
host = '[%s]' % host
else:
# Otherwise use the provided hostname.
host = info.server.rstrip('.')
return ('{proto}://{host}:{port}{path}'.format(proto=protocol,
host=host,
port=info.port,
path=path),
properties)
[docs]
def close(self):
"""Shut down mDNS and unregister services.
.. note::
If another server is running for the same services, it will
re-register them immediately.
"""
for info in self._registered:
try:
self._zc.unregister_service(info)
except Exception:
LOG.exception('Cound not unregister mDNS service %s', info)
self._zc.close()
def __enter__(self):
return self
def __exit__(self, *args):
self.close()
[docs]
def get_endpoint(service_type):
"""Get an endpoint and its properties from mDNS.
If the requested endpoint is already in the built-in server cache, and
its TTL is not exceeded, the cached value is returned.
:param service_type: OpenStack service type.
:returns: tuple (endpoint URL, properties as a dict).
:raises: :exc:`.ServiceLookupFailure` if the service cannot be found.
"""
with Zeroconf() as zc:
return zc.get_endpoint(service_type)
[docs]
def list_opts():
"""Entry point for oslo-config-generator."""
return [('mdns', opts)]
