nova conductor running on a rhel8 host inside f28 based containers hits the following error:
2019-01-17 13:59:37.049 46 DEBUG oslo_concurrency.lockutils [req-284f3071-8eee-4dcb-903c-838f2e024b48 40ca1490773f49f791d3a834af3702c8 8671bdf05abf48f58a9bdcdb0ef4b740 - default default] Lock "b051d003-482d-4cb7-810c-8d256e6c879e" acquired by "nova.context.set_target_cell.<locals>.get_or_set_cached_cell_and_set_connections" :: waited 0.000s inner /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:327
2019-01-17 13:59:37.050 46 DEBUG oslo_concurrency.lockutils [req-284f3071-8eee-4dcb-903c-838f2e024b48 40ca1490773f49f791d3a834af3702c8 8671bdf05abf48f58a9bdcdb0ef4b740 - default default] Lock "b051d003-482d-4cb7-810c-8d256e6c879e" released by "nova.context.set_target_cell.<locals>.get_or_set_cached_cell_and_set_connections" :: held 0.002s inner /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:339
2019-01-17 13:59:37.060 46 DEBUG oslo_db.sqlalchemy.engines [req-284f3071-8eee-4dcb-903c-838f2e024b48 40ca1490773f49f791d3a834af3702c8 8671bdf05abf48f58a9bdcdb0ef4b740 - default default] MySQL server mode set to STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,TRADITIONAL,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION _check_effective_sql_mode /usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/engines.py:307
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server [req-284f3071-8eee-4dcb-903c-838f2e024b48 40ca1490773f49f791d3a834af3702c8 8671bdf05abf48f58a9bdcdb0ef4b740 - default default] Exception during message handling: TypeError: object() takes no parameters
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/_memcache_pool.py", line 163, in _get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     conn = self.queue.pop().connection
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server IndexError: pop from an empty deque
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server During handling of the above exception, another exception occurred:
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_messaging/rpc/server.py", line 166, in _process_incoming
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     res = self.dispatcher.dispatch(message)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_messaging/rpc/dispatcher.py", line 265, in dispatch
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     return self._do_dispatch(endpoint, method, ctxt, args)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_messaging/rpc/dispatcher.py", line 194, in _do_dispatch
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     result = func(ctxt, **new_args)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/conductor/manager.py", line 1303, in schedule_and_build_instances
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     instance.create()
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_versionedobjects/base.py", line 226, in wrapper
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     return fn(self, *args, **kwargs)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/objects/instance.py", line 607, in create
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     self._load_ec2_ids()
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/objects/instance.py", line 983, in _load_ec2_ids
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     self.ec2_ids = objects.EC2Ids.get_by_instance(self._context, self)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_versionedobjects/base.py", line 184, in wrapper
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     result = fn(cls, context, *args, **kwargs)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/objects/ec2.py", line 216, in get_by_instance
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     ec2_ids = cls._get_ec2_ids(context, instance)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/objects/ec2.py", line 200, in _get_ec2_ids
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     ec2_ids['instance_id'] = ec2utils.id_to_ec2_inst_id(instance.uuid)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/api/ec2/ec2utils.py", line 188, in id_to_ec2_inst_id
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     int_id = get_int_id_from_instance_uuid(ctxt, instance_id)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/api/ec2/ec2utils.py", line 47, in memoizer
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     value = _CACHE.get(key)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/nova/cache_utils.py", line 107, in get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     value = self.region.get(key)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/dogpile/cache/region.py", line 645, in get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     value = self.backend.get(key)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/dogpile/cache/backends/memcached.py", line 161, in get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     value = self.client.get(key)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/backends/memcache_pool.py", line 31, in _run_method
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     with self.client_pool.acquire() as client:
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib64/python3.6/contextlib.py", line 81, in __enter__
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     return next(self.gen)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/_memcache_pool.py", line 128, in acquire
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     conn = self.get(timeout=self._connection_get_timeout)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/eventlet/queue.py", line 303, in get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     return self._get()
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/_memcache_pool.py", line 214, in _get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     conn = ConnectionPool._get(self)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/_memcache_pool.py", line 165, in _get
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     conn = self._create_connection()
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server   File "/usr/lib/python3.6/site-packages/oslo_cache/_memcache_pool.py", line 206, in _create_connection
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server     return _MemcacheClient(self.urls, **self._arguments)
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server TypeError: object() takes no parameters
2019-01-17 13:59:37.096 46 ERROR oslo_messaging.rpc.server

nova.conf has:
()[nova@standalone /]$ grep -v ^# /etc/nova/nova.conf |grep '[a-zA-Z]' |grep -i mem
backend=oslo_cache.memcache_pool
memcache_servers=192.168.24.2:11211
memcached_servers=192.168.24.2:11211

memcache seems to be up:
[root@standalone ~]# podman top memcached
USER        PID   PPID   %CPU    ELAPSED             TTY   TIME   COMMAND
memcached   1     0      0.000   2h2m27.45050385s    ?     0s     dumb-init --single-child -- /bin/bash -c source /etc/sysconfig/memcached; /usr/bin/memcached -p ${PORT} -u ${USER} -m ${CACHESIZE} -c ${MAXCONN} $OPTIONS 
memcached   8     1      0.000   2h2m27.450722828s   ?     0s     /bin/bash -c source /etc/sysconfig/memcached; /usr/bin/memcached -p ${PORT} -u ${USER} -m ${CACHESIZE} -c ${MAXCONN} $OPTIONS 
memcached   9     8      0.000   2h2m27.450781466s   ?     0s     /usr/bin/memcached -p 11211 -u memcached -m 11970 -c 8192 -v -l 192.168.24.2 -U 0 -X -t 8 >> /var/log/memcached.log 2>&1 

Workaround:
disable caching in nova
crudini --set /var/lib/config-data/puppet-generated/nova/etc/nova/nova.conf cache enabled false
podman restart nova_conductor

Versions inside the f28 nova-conductor container:
python-oslo-versionedobjects-lang-1.34.1-0.20181128123056.50474ad.fc28.noarch
python3-oslo-config-6.7.0-0.20181108120643.64e020a.fc28.noarch
python3-oslo-cache-1.32.0-0.20190108083242.eb68d73.fc28.noarch
python3-oslo-versionedobjects-1.34.1-0.20181128123056.50474ad.fc28.noarch
python-oslo-middleware-lang-3.37.0-0.20181211135004.a609e68.fc28.noarch
puppet-oslo-14.2.0-0.20190111032249.b937844.fc28.noarch
python3-oslo-middleware-3.37.0-0.20181211135004.a609e68.fc28.noarch
python3-oslo-service-1.34.0-0.20190114140259.d987a4a.fc28.noarch
python3-oslo-policy-1.44.0-0.20190108082943.c9ea8f7.fc28.noarch
python-oslo-policy-lang-1.44.0-0.20190108082943.c9ea8f7.fc28.noarch
python-oslo-concurrency-lang-3.29.0-0.20181128184857.0767ddf.fc28.noarch
python3-oslo-utils-3.39.0-0.20190110184625.3823707.fc28.noarch
python3-oslo-vmware-2.32.1-0.20181126101324.04f82ae.fc28.noarch
python-oslo-log-lang-3.42.2-0.20190114115634.1babd44.fc28.noarch
python3-oslo-rootwrap-5.15.1-0.20181226111925.27f2314.fc28.noarch
python3-oslo-context-2.22.0-0.20190114134914.f65408d.fc28.noarch
python3-oslo-privsep-1.30.1-0.20181127103633.9391cbf.fc28.noarch
python-oslo-utils-lang-3.39.0-0.20190110184625.3823707.fc28.noarch
python-oslo-db-lang-4.43.0-0.20190108081838.a6d2cc5.fc28.noarch
python3-memcached-1.58-5.fc29.noarch
python-oslo-cache-lang-1.32.0-0.20190108083242.eb68d73.fc28.noarch
python3-oslo-i18n-3.23.0-0.20190111201133.a5fde9a.fc28.noarch
python3-oslo-concurrency-3.29.0-0.20181128184857.0767ddf.fc28.noarch
python3-oslo-db-4.43.0-0.20190108081838.a6d2cc5.fc28.noarch
python3-oslo-reports-1.29.1-0.20181126102912.dde49a4.fc28.noarch
python-oslo-i18n-lang-3.23.0-0.20190111201133.a5fde9a.fc28.noarch
python3-oslo-messaging-9.3.0-0.20190114135848.13fa4f5.fc28.noarch
python3-oslo-serialization-2.28.1-0.20181001122254.0371c1d.fc28.noarch
python-oslo-vmware-lang-2.32.1-0.20181126101324.04f82ae.fc28.noarch
python-oslo-privsep-lang-1.30.1-0.20181127103633.9391cbf.fc28.noarch
python3-oslo-log-3.42.2-0.20190114115634.1babd44.fc28.noarch
puppet-memcached-3.3.0-0.20180803162752.e517b44.fc28.noarch