20 files changed, 405 insertions, 124 deletions
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 9d94556..08aef91 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -9,7 +9,7 @@ default_language_version:
 
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: ebc15addedad713c86ef18ae9632c88e187dd0af  # v3.1.0
+    rev: 9136088a246768144165fcc3ecc3d31bb686920a # v3.3.0
     hooks:
       - id: trailing-whitespace
       # Replaces or checks mixed line ending
@@ -27,9 +27,13 @@ repos:
       - id: debug-statements
       - id: check-yaml
         files: .*\.(yaml|yml)$
-  - repo: https://gitlab.com/pycqa/flake8
-    rev: 181bb46098dddf7e2d45319ea654b4b4d58c2840 # 3.8.3
+  - repo: local
     hooks:
       - id: flake8
+        name: flake8
         additional_dependencies:
           - hacking>=3.0.1,<3.1.0
+        language: python
+        entry: flake8
+        files: '^.*\.py$'
+        exclude: '^(doc|releasenotes|tools)/.*$'
diff --git a/.zuul.d/project.yaml b/.zuul.yaml
index 1155b74..8425030 100644
--- a/.zuul.d/project.yaml
+++ b/.zuul.yaml
@@ -2,7 +2,6 @@
     templates:
       - check-requirements
       - lib-forward-testing-python3
-      - openstack-lower-constraints-jobs
       - openstack-python3-wallaby-jobs
       - periodic-stable-jobs
       - publish-openstack-docs-pti
diff --git a/doc/source/cli/validator.rst b/doc/source/cli/validator.rst
index d829b8d..23ae424 100644
--- a/doc/source/cli/validator.rst
+++ b/doc/source/cli/validator.rst
@@ -32,7 +32,7 @@ Here's an example of using the validator on Nova as installed by Devstack (with
 the option [foo]/bar added to demonstrate a failure)::
 
     $ oslo-config-validator --config-file /opt/stack/nova/etc/nova/nova-config-generator.conf --input-file /etc/nova/nova.conf
-    ERROR:root:foo/bar not found
+    ERROR:root:foo/bar is not part of the sample config
     INFO:root:Ignoring missing option "project_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
     INFO:root:Ignoring missing option "project_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
     INFO:root:Ignoring missing option "user_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
@@ -58,7 +58,7 @@ a sample config file ``config-data.yaml`` created by the config generator (with
 the option [foo]/bar added to demonstrate a failure)::
 
     $ oslo-config-validator --opt-data config-data.yaml --input-file /etc/nova/nova.conf
-    ERROR:root:foo/bar not found
+    ERROR:root:foo/bar is not part of the sample config
     INFO:root:Ignoring missing option "project_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
     INFO:root:Ignoring missing option "project_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
     INFO:root:Ignoring missing option "user_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
@@ -66,6 +66,158 @@ the option [foo]/bar added to demonstrate a failure)::
     INFO:root:Ignoring missing option "username" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
     INFO:root:Ignoring missing option "auth_url" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
 
+Comparing configuration with the default configuration
+------------------------------------------------------
+
+.. note:: For most accurate results, the validation should be done using the
+          same version of the code as the system whose config file is being
+          validated.
+
+Comparing the default configuration with the current configuration can help
+operators with troubleshooting issues. Since the generator config is not always
+available in production environment, we can pass the ``--namespace`` arguments.
+In addition to the ``--namespace``, we need to pass a ``--input-file`` as well
+as the ``--check-defaults``.
+
+Some options are ignored by default but this behavior can be overridden with
+the ``--exclude-options`` list argument.
+
+Here's an example of using the validator on Nova::
+
+    $ oslo-config-validator --input-file /etc/nova/nova.conf \
+                            --check-defaults \
+                            --namespace nova.conf \
+                            --namespace oslo.log \
+                            --namespace oslo.messaging \
+                            --namespace oslo.policy \
+                            --namespace oslo.privsep \
+                            --namespace oslo.service.periodic_task \
+                            --namespace oslo.service.service \
+                            --namespace oslo.db \
+                            --namespace oslo.db.concurrency \
+                            --namespace oslo.middleware \
+                            --namespace oslo.concurrency \
+                            --namespace keystonemiddleware.auth_token \
+                            --namespace osprofiler
+    INFO:keyring.backend:Loading Gnome
+    INFO:keyring.backend:Loading Google
+    INFO:keyring.backend:Loading Windows (alt)
+    INFO:keyring.backend:Loading file
+    INFO:keyring.backend:Loading keyczar
+    INFO:keyring.backend:Loading multi
+    INFO:keyring.backend:Loading pyfs
+    WARNING:root:DEFAULT/compute_driver sample value is empty but input-file has libvirt.LibvirtDriver
+    WARNING:root:DEFAULT/allow_resize_to_same_host sample value is empty but input-file has True
+    WARNING:root:DEFAULT/default_ephemeral_format sample value is empty but input-file has ext4
+    WARNING:root:DEFAULT/pointer_model sample value ['usbtablet'] is not in ['ps2mouse']
+    WARNING:root:DEFAULT/instances_path sample value ['$state_path/instances'] is not in ['/opt/stack/data/nova/instances']
+    WARNING:root:DEFAULT/shutdown_timeout sample value ['60'] is not in ['0']
+    INFO:root:DEFAULT/my_ip Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:DEFAULT/state_path sample value ['$pybasedir'] is not in ['/opt/stack/data/nova']
+    INFO:root:DEFAULT/osapi_compute_listen Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:DEFAULT/osapi_compute_workers sample value is empty but input-file has 2
+    WARNING:root:DEFAULT/metadata_workers sample value is empty but input-file has 2
+    WARNING:root:DEFAULT/graceful_shutdown_timeout sample value ['60'] is not in ['5']
+    INFO:root:DEFAULT/transport_url Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:DEFAULT/debug sample value is empty but input-file has True
+    WARNING:root:DEFAULT/logging_context_format_string sample value ['%(asctime)s.%(msecs)03d %(process)d %(levelname)s %(name)s [%(request_id)s %(user_identity)s] %(instance)s%(message)s'] is not in ['%(color)s%(levelname)s %(name)s [\x1b[01;36m%(global_request_id)s %(request_id)s \x1b[00;36m%(project_name)s %(user_name)s%(color)s] \x1b[01;35m%(instance)s%(color)s%(message)s\x1b[00m']
+    WARNING:root:DEFAULT/logging_default_format_string sample value ['%(asctime)s.%(msecs)03d %(process)d %(levelname)s %(name)s [-] %(instance)s%(message)s'] is not in ['%(color)s%(levelname)s %(name)s [\x1b[00;36m-%(color)s] \x1b[01;35m%(instance)s%(color)s%(message)s\x1b[00m']
+    WARNING:root:DEFAULT/logging_debug_format_suffix sample value ['%(funcName)s %(pathname)s:%(lineno)d'] is not in ['\x1b[00;33m{{(pid=%(process)d) %(funcName)s %(pathname)s:%(lineno)d}}\x1b[00m']
+    WARNING:root:DEFAULT/logging_exception_prefix sample value ['%(asctime)s.%(msecs)03d %(process)d ERROR %(name)s %(instance)s'] is not in ['ERROR %(name)s \x1b[01;35m%(instance)s\x1b[00m']
+    WARNING:root:Group api from the sample config is not defined in input-file
+    WARNING:root:cache/backend sample value ['dogpile.cache.null'] is not in ['dogpile.cache.memcached']
+    WARNING:root:cache/enabled sample value is empty but input-file has True
+    WARNING:root:cinder/os_region_name sample value is empty but input-file has RegionOne
+    WARNING:root:cinder/auth_type sample value is empty but input-file has password
+    INFO:root:cinder/auth_url Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:cinder/project_name sample value is empty but input-file has service
+    WARNING:root:cinder/project_domain_name sample value is empty but input-file has Default
+    INFO:root:cinder/username Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:cinder/user_domain_name sample value is empty but input-file has Default
+    INFO:root:cinder/password Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:Group compute from the sample config is not defined in input-file
+    WARNING:root:conductor/workers sample value is empty but input-file has 2
+    WARNING:root:Group console from the sample config is not defined in input-file
+    WARNING:root:Group consoleauth from the sample config is not defined in input-file
+    WARNING:root:Group cyborg from the sample config is not defined in input-file
+    INFO:root:api_database/connection Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:Group devices from the sample config is not defined in input-file
+    WARNING:root:Group ephemeral_storage_encryption from the sample config is not defined in input-file
+    WARNING:root:Group glance from the sample config is not defined in input-file
+    WARNING:root:Group guestfs from the sample config is not defined in input-file
+    WARNING:root:Group hyperv from the sample config is not defined in input-file
+    WARNING:root:Group image_cache from the sample config is not defined in input-file
+    WARNING:root:Group ironic from the sample config is not defined in input-file
+    WARNING:root:key_manager/fixed_key sample value is empty but input-file has bae3516cc1c0eb18b05440eba8012a4a880a2ee04d584a9c1579445e675b12defdc716ec
+    WARNING:root:key_manager/backend sample value ['barbican'] is not in ['nova.keymgr.conf_key_mgr.ConfKeyManager']
+    WARNING:root:Group barbican from the sample config is not defined in input-file
+    WARNING:root:Group vault from the sample config is not defined in input-file
+    WARNING:root:Group keystone from the sample config is not defined in input-file
+    INFO:root:libvirt/live_migration_uri Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:libvirt/cpu_mode sample value is empty but input-file has none
+    WARNING:root:Group mks from the sample config is not defined in input-file
+    WARNING:root:neutron/default_floating_pool sample value ['nova'] is not in ['public']
+    WARNING:root:neutron/service_metadata_proxy sample value is empty but input-file has True
+    WARNING:root:neutron/auth_type sample value is empty but input-file has password
+    INFO:root:neutron/auth_url Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:neutron/project_name sample value is empty but input-file has service
+    WARNING:root:neutron/project_domain_name sample value is empty but input-file has Default
+    INFO:root:neutron/username Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:neutron/user_domain_name sample value is empty but input-file has Default
+    INFO:root:neutron/password Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:neutron/region_name sample value is empty but input-file has RegionOne
+    WARNING:root:Group pci from the sample config is not defined in input-file
+    WARNING:root:placement/auth_type sample value is empty but input-file has password
+    INFO:root:placement/auth_url Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:placement/project_name sample value is empty but input-file has service
+    WARNING:root:placement/project_domain_name sample value is empty but input-file has Default
+    INFO:root:placement/username Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:placement/user_domain_name sample value is empty but input-file has Default
+    INFO:root:placement/password Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:placement/region_name sample value is empty but input-file has RegionOne
+    WARNING:root:Group powervm from the sample config is not defined in input-file
+    WARNING:root:Group quota from the sample config is not defined in input-file
+    WARNING:root:Group rdp from the sample config is not defined in input-file
+    WARNING:root:Group remote_debug from the sample config is not defined in input-file
+    WARNING:root:scheduler/workers sample value is empty but input-file has 2
+    WARNING:root:filter_scheduler/track_instance_changes sample value ['True'] is not in ['False']
+    WARNING:root:filter_scheduler/enabled_filters sample value ['AvailabilityZoneFilter', 'ComputeFilter', 'ComputeCapabilitiesFilter', 'ImagePropertiesFilter', 'ServerGroupAntiAffinityFilter', 'ServerGroupAffinityFilter'] is not in ['AvailabilityZoneFilter,ComputeFilter,ComputeCapabilitiesFilter,ImagePropertiesFilter,ServerGroupAntiAffinityFilter,ServerGroupAffinityFilter,SameHostFilter,DifferentHostFilter']
+    WARNING:root:Group metrics from the sample config is not defined in input-file
+    WARNING:root:Group serial_console from the sample config is not defined in input-file
+    WARNING:root:Group service_user from the sample config is not defined in input-file
+    WARNING:root:Group spice from the sample config is not defined in input-file
+    WARNING:root:upgrade_levels/compute sample value is empty but input-file has auto
+    WARNING:root:Group vendordata_dynamic_auth from the sample config is not defined in input-file
+    WARNING:root:Group vmware from the sample config is not defined in input-file
+    WARNING:root:Group vnc from the sample config is not defined in input-file
+    WARNING:root:Group workarounds from the sample config is not defined in input-file
+    WARNING:root:wsgi/api_paste_config sample value ['api-paste.ini'] is not in ['/etc/nova/api-paste.ini']
+    WARNING:root:Group zvm from the sample config is not defined in input-file
+    WARNING:root:oslo_concurrency/lock_path sample value is empty but input-file has /opt/stack/data/nova
+    WARNING:root:Group oslo_middleware from the sample config is not defined in input-file
+    WARNING:root:Group cors from the sample config is not defined in input-file
+    WARNING:root:Group healthcheck from the sample config is not defined in input-file
+    WARNING:root:Group oslo_messaging_amqp from the sample config is not defined in input-file
+    WARNING:root:oslo_messaging_notifications/driver sample value is empty but input-file has messagingv2
+    INFO:root:oslo_messaging_notifications/transport_url Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:Group oslo_messaging_rabbit from the sample config is not defined in input-file
+    WARNING:root:Group oslo_messaging_kafka from the sample config is not defined in input-file
+    WARNING:root:Group oslo_policy from the sample config is not defined in input-file
+    WARNING:root:Group privsep from the sample config is not defined in input-file
+    WARNING:root:Group profiler from the sample config is not defined in input-file
+    INFO:root:database/connection Ignoring option because it is part of the excluded patterns. This can be changed with the --exclude-options argument.
+    WARNING:root:keystone_authtoken/interface sample value ['internal'] is not in ['public']
+    WARNING:root:keystone_authtoken/cafile sample value is empty but input-file has /opt/stack/data/ca-bundle.pem
+    WARNING:root:keystone_authtoken/memcached_servers sample value is empty but input-file has localhost:11211
+    WARNING:root:keystone_authtoken/auth_type sample value is empty but input-file has password
+    ERROR:root:neutron/auth_strategy is not part of the sample config
+    INFO:root:Ignoring missing option "project_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
+    INFO:root:Ignoring missing option "project_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
+    INFO:root:Ignoring missing option "user_domain_name" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
+    INFO:root:Ignoring missing option "password" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
+    INFO:root:Ignoring missing option "username" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly.
+    INFO:root:Ignoring missing option "auth_url" from group "keystone_authtoken" because the group is known to have incomplete sample config data and thus cannot be validated properly
+
 Handling Dynamic Groups
 -----------------------
 
diff --git a/doc/source/reference/configuration-files.rst b/doc/source/reference/configuration-files.rst
index b4e299d..435a135 100644
--- a/doc/source/reference/configuration-files.rst
+++ b/doc/source/reference/configuration-files.rst
@@ -7,7 +7,7 @@ and ``--config-dir``:
 
 .. code-block:: python
 
-    class ConfigOpts(object):
+    class ConfigOpts:
 
         def __call__(self, ...):
 
diff --git a/doc/source/reference/defining.rst b/doc/source/reference/defining.rst
index d8e1866..19a70ec 100644
--- a/doc/source/reference/defining.rst
+++ b/doc/source/reference/defining.rst
@@ -81,7 +81,7 @@ the option is referenced:
 
 .. code-block:: python
 
-    class ExtensionManager(object):
+    class ExtensionManager:
 
         enabled_apis_opt = cfg.ListOpt(...)
 
diff --git a/lower-constraints.txt b/lower-constraints.txt
deleted file mode 100644
index fc28af9..0000000
--- a/lower-constraints.txt
+++ /dev/null
@@ -1,80 +0,0 @@
-alabaster==0.7.10
-appdirs==1.3.0
-Babel==2.3.4
-certifi==2020.4.5.2
-chardet==3.0.4
-cliff==3.1.0
-cmd2==0.8.9
-coverage==4.0
-debtcollector==1.2.0
-doc8==0.8.1
-docutils==0.11
-dulwich==0.15.0
-entrypoints==0.3
-extras==1.0.0
-fixtures==3.0.0
-future==0.18.2
-gitdb==0.6.4
-GitPython==1.0.1
-idna==2.5
-imagesize==0.7.1
-importlib_metadata==1.7.0
-iso8601==0.1.11
-Jinja2==2.10
-keystoneauth1==3.4.0
-linecache2==1.0.0
-MarkupSafe==1.0
-mock==4.0.2
-monotonic==1.5
-mox3==0.20.0
-msgpack==1.0.0
-mypy==0.720
-mypy-extensions==0.4.3
-netaddr==0.7.18
-netifaces==0.10.9
-openstackdocstheme==1.20.0
-os-client-config==1.28.0
-oslo.context==3.1.0
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.serialization==3.2.0
-oslo.utils==4.2.0
-oslotest==3.2.0
-packaging==20.4
-pbr==2.0.0
-prettytable==0.7.2
-Pygments==2.2.0
-pyinotify==0.9.6
-pyparsing==2.4.7
-pyperclip==1.8.0
-python-dateutil==2.8.1
-python-mimeparse==1.6.0
-python-subunit==1.0.0
-pytz==2013.6
-PyYAML==3.12
-reno==2.5.0
-requests==2.18.0
-requests-mock==1.5.0
-requestsexceptions==1.2.0
-restructuredtext-lint==1.3.1
-rfc3986==1.2.0
-rst2txt==1.1.0
-six==1.15.0
-smmap==0.9.0
-snowballstemmer==1.2.1
-Sphinx==1.8.0
-sphinxcontrib-apidoc==0.3.0
-sphinxcontrib-websupport==1.0.1
-stestr==2.1.0
-stevedore==1.20.0
-testrepository==0.0.20
-testscenarios==0.4
-testtools==2.2.0
-traceback2==1.4.0
-typed-ast==1.4.1
-typing-extensions==3.7.4.2
-unittest2==1.1.0
-urllib3==1.21.1
-voluptuous==0.11.7
-wcwidth==0.2.4
-wrapt==1.7.0
diff --git a/oslo_config/cfg.py b/oslo_config/cfg.py
index 5324e52..39a9878 100644
--- a/oslo_config/cfg.py
+++ b/oslo_config/cfg.py
@@ -424,7 +424,7 @@ def _report_deprecation(format_str, format_dict):
 
 
 @functools.total_ordering
-class Opt(object):
+class Opt:
 
     """Base class for all configuration options.
 
@@ -809,7 +809,7 @@ class Opt(object):
         return hash(self) < hash(another)
 
 
-class DeprecatedOpt(object):
+class DeprecatedOpt:
 
     """Represents a Deprecated option.
 
@@ -1416,7 +1416,7 @@ class _ConfigDirOpt(Opt):
         return kwargs
 
 
-class OptGroup(object):
+class OptGroup:
 
     """Represents a group of opts.
 
@@ -3155,7 +3155,7 @@ class ConfigOpts(abc.Mapping):
             """Return the number of options and option groups."""
             return len(self._group._opts)
 
-    class SubCommandAttr(object):
+    class SubCommandAttr:
 
         """Helper class.
 
@@ -3189,7 +3189,7 @@ class ConfigOpts(abc.Mapping):
             except AttributeError:
                 raise NoSuchOptError(name)
 
-    class StrSubWrapper(object):
+    class StrSubWrapper:
 
         """Helper class.
 
diff --git a/oslo_config/generator.py b/oslo_config/generator.py
index 277036b..9fdde09 100644
--- a/oslo_config/generator.py
+++ b/oslo_config/generator.py
@@ -174,7 +174,7 @@ def _format_type_name(opt_type):
     return 'unknown value'
 
 
-class _OptFormatter(object):
+class _OptFormatter:
 
     """Format configuration option descriptions to a file."""
 
diff --git a/oslo_config/iniparser.py b/oslo_config/iniparser.py
index 90218e4..b79ee08 100644
--- a/oslo_config/iniparser.py
+++ b/oslo_config/iniparser.py
@@ -23,7 +23,7 @@ class ParseError(Exception):
         return 'at line %d, %s: %r' % (self.lineno, self.msg, self.line)
 
 
-class BaseParser(object):
+class BaseParser:
     lineno = 0
     parse_exc = ParseError
 
diff --git a/oslo_config/sources/__init__.py b/oslo_config/sources/__init__.py
index 92b557d..a1fa0c5 100644
--- a/oslo_config/sources/__init__.py
+++ b/oslo_config/sources/__init__.py
@@ -33,10 +33,10 @@ import abc
 _NoValue = object()
 
 
-class ConfigurationSourceDriver(object, metaclass=abc.ABCMeta):
+class ConfigurationSourceDriver(metaclass=abc.ABCMeta):
     """A backend driver option for oslo.config.
 
-    For each group name listed in **config_source** on the **DEFAULT** group,
+    For each group name listed in **config_source** in the **DEFAULT** group,
     a :class:`ConfigurationSourceDriver` is responsible for creating one new
     instance of a :class:`ConfigurationSource`. The proper driver class to be
     used is selected based on the **driver** option inside each one of the
@@ -96,7 +96,7 @@ class ConfigurationSourceDriver(object, metaclass=abc.ABCMeta):
         """
 
 
-class ConfigurationSource(object, metaclass=abc.ABCMeta):
+class ConfigurationSource(metaclass=abc.ABCMeta):
     """A configuration source option for oslo.config.
 
     A configuration source is able to fetch configuration values based on
diff --git a/oslo_config/tests/test_cfg.py b/oslo_config/tests/test_cfg.py
index ac45780..505cb00 100644
--- a/oslo_config/tests/test_cfg.py
+++ b/oslo_config/tests/test_cfg.py
@@ -3958,7 +3958,7 @@ class FindFileTestCase(BaseTestCase):
 
 class OptDumpingTestCase(BaseTestCase):
 
-    class FakeLogger(object):
+    class FakeLogger:
 
         def __init__(self, test_case, expected_lvl):
             self.test_case = test_case
diff --git a/oslo_config/tests/test_generator.py b/oslo_config/tests/test_generator.py
index 9a27aac..d75b4d8 100644
--- a/oslo_config/tests/test_generator.py
+++ b/oslo_config/tests/test_generator.py
@@ -1638,7 +1638,7 @@ class GeneratorRaiseErrorTestCase(base.BaseTestCase):
         class FakeException(Exception):
             pass
 
-        class FakeEP(object):
+        class FakeEP:
 
             def __init__(self):
                 self.name = 'callback_is_expected'
diff --git a/oslo_config/tests/test_types.py b/oslo_config/tests/test_types.py
index 644a239..dd56b98 100644
--- a/oslo_config/tests/test_types.py
+++ b/oslo_config/tests/test_types.py
@@ -37,7 +37,7 @@ class ConfigTypeTests(unittest.TestCase):
         MyString()
 
 
-class TypeTestHelper(object):
+class TypeTestHelper:
     def setUp(self):
         super(TypeTestHelper, self).setUp()
         self.type_instance = self.type
@@ -766,6 +766,27 @@ class HostAddressTypeTests(TypeTestHelper, unittest.TestCase):
         self.assertConvertedValue('abc.0-0', 'abc.0-0')
 
 
+class HostDomainTypeTests(TypeTestHelper, unittest.TestCase):
+    type = types.HostDomain()
+
+    def test_invalid_host_addresses(self):
+        self.assertInvalid('-1')
+        self.assertInvalid('3.14')
+        self.assertInvalid('10.0')
+        self.assertInvalid('host..name')
+        self.assertInvalid('org.10')
+        self.assertInvalid('0.0.00')
+
+    def test_valid_host_addresses(self):
+        self.assertConvertedValue('_foo', '_foo')
+        self.assertConvertedValue('host_name', 'host_name')
+        self.assertConvertedValue(
+            'overcloud-novacompute_edge1-0.internalapi.localdomain',
+            'overcloud-novacompute_edge1-0.internalapi.localdomain')
+        self.assertConvertedValue('host_01.co.uk', 'host_01.co.uk')
+        self.assertConvertedValue('_site01001', '_site01001')
+
+
 class HostnameTypeTests(TypeTestHelper, unittest.TestCase):
     type = types.Hostname()
 
@@ -796,8 +817,8 @@ class HostnameTypeTests(TypeTestHelper, unittest.TestCase):
         self.assertInvalid("h'ost'")
         self.assertInvalid("h'ost")
         self.assertInvalid("h$ost")
-        self.assertInvalid("h%ost")
         self.assertInvalid("host_01.co.uk")
+        self.assertInvalid("h%ost")
         self.assertInvalid("host;name=99")
         self.assertInvalid('___site0.1001')
         self.assertInvalid('_site01001')
@@ -808,6 +829,7 @@ class HostnameTypeTests(TypeTestHelper, unittest.TestCase):
     def test_invalid_hostnames_with_numeric_characters(self):
         self.assertInvalid("10.0.0.0")
         self.assertInvalid("3.14")
+        self.assertInvalid('___site0.1001')
         self.assertInvalid("org.10")
         self.assertInvalid('0.0.00')
 
diff --git a/oslo_config/tests/test_validator.py b/oslo_config/tests/test_validator.py
index de912ac..383340f 100644
--- a/oslo_config/tests/test_validator.py
+++ b/oslo_config/tests/test_validator.py
@@ -21,13 +21,51 @@ from oslo_config import fixture
 from oslo_config import validator
 
 
-OPT_DATA = {'options': {'foo': {'opts': [{'name': 'opt'}]},
-                        'bar': {'opts': [{'name': 'opt'}]},
-                        },
-            'deprecated_options': {'bar': [{'name': 'opt'}]}}
+OPT_DATA = {
+  "options": {
+    "foo": {
+      "opts": [
+        {
+          "name": "opt",
+          "default": 1
+        }
+      ]
+    },
+    "bar": {
+      "opts": [
+        {
+          "name": "opt",
+          "default": 2
+        },
+        {
+          "name": "foo-bar",
+          "dest": "foo_bar",
+          "default": 2
+        },
+        {
+          "name": "bar-foo",
+          "dest": "bar_foo",
+          "default": 2
+        }
+      ]
+    }
+  },
+  "deprecated_options": {
+    "bar": [
+      {
+        "name": "opt",
+        "default": 3
+      }
+    ]
+  }
+}
 VALID_CONF = """
 [foo]
-opt = value
+opt = 1
+[bar]
+opt = 3
+foo-bar = 3
+bar_foo = 3
 """
 DEPRECATED_CONF = """
 [bar]
@@ -106,5 +144,15 @@ class TestValidator(base.BaseTestCase):
         with mock.patch('builtins.open', m):
             self.assertEqual(0, validator._validate(self.conf))
 
+    @mock.patch('oslo_config.validator.load_opt_data')
+    def test_check_defaults(self, mock_lod):
+        mock_lod.return_value = OPT_DATA
+        self.conf_fixture.config(opt_data='mocked.yaml',
+                                 input_file='mocked.conf',
+                                 check_defaults=True)
+        m = mock.mock_open(read_data=VALID_CONF)
+        with mock.patch('builtins.open', m):
+            self.assertEqual(0, validator._validate(self.conf))
+
     def test_invalid_options(self):
         self.assertRaises(RuntimeError, validator._validate, self.conf)
diff --git a/oslo_config/types.py b/oslo_config/types.py
index dfd89bc..72242cb 100644
--- a/oslo_config/types.py
+++ b/oslo_config/types.py
@@ -30,7 +30,7 @@ import netaddr
 import rfc3986
 
 
-class ConfigType(object, metaclass=abc.ABCMeta):
+class ConfigType(metaclass=abc.ABCMeta):
 
     def __init__(self, type_name='unknown type'):
         self.type_name = type_name
@@ -761,11 +761,12 @@ class Hostname(ConfigType):
     :param type_name: Type name to be used in the sample config file.
 
     """
+    HOSTNAME_REGEX = '(?!-)[A-Z0-9-]{1,63}(?<!-)$'
 
     def __init__(self, type_name='hostname value'):
         super(Hostname, self).__init__(type_name=type_name)
 
-    def __call__(self, value):
+    def __call__(self, value, regex=HOSTNAME_REGEX):
         """Check hostname is valid.
 
         Ensures that each segment
@@ -789,7 +790,7 @@ class Hostname(ConfigType):
                              % value)
         if value.endswith("."):
             value = value[:-1]
-        allowed = re.compile("(?!-)[A-Z0-9-]{1,63}(?<!-)$", re.IGNORECASE)
+        allowed = re.compile(regex, re.IGNORECASE)
         if not re.search('[a-zA-Z-]', value.split(".")[-1]):
             raise ValueError('%s contains no non-numeric characters in the '
                              'top-level domain part of the host name and is '
@@ -844,7 +845,8 @@ class HostAddress(ConfigType):
             try:
                 value = self.hostname(value)
             except ValueError:
-                raise ValueError("%s is not a valid host address" % (value,))
+                raise ValueError(
+                    "%s is not a valid host address" % (value,))
         return value
 
     def __repr__(self):
@@ -857,6 +859,45 @@ class HostAddress(ConfigType):
         return value
 
 
+class HostDomain(HostAddress):
+    """Host Domain type.
+
+    Like HostAddress with the support of _ character.
+
+    :param version: defines which version should be explicitly
+                    checked (4 or 6) in case of an IP address
+    :param type_name: Type name to be used in the sample config file.
+    """
+    # DOMAIN_REGEX is HOSTNAME_REGEX with the _ character added
+    DOMAIN_REGEX = '(?!-)[A-Z0-9-_]{1,63}(?<!-)$'
+
+    def __call__(self, value):
+        """Checks if is a valid IP/hostname.
+
+        If not a valid IP, makes sure it is not a mistyped IP before
+        performing checks for it as a hostname.
+
+        """
+
+        try:
+            value = super(HostDomain, self).__call__(value)
+        except ValueError:
+            # Check if domain is valid
+            # Add support of underscore
+            # https://www.ietf.org/rfc/rfc1912,
+            # http://domainkeys.sourceforge.net/underscore.html
+            # https://bugs.launchpad.net/oslo.config/+bug/1892044
+            try:
+                value = self.hostname(value, regex=self.DOMAIN_REGEX)
+            except ValueError:
+                raise ValueError(
+                    "%s is not a valid host address" % (value,))
+        return value
+
+    def __repr__(self):
+        return 'HostDomain'
+
+
 class URI(ConfigType):
 
     """URI type
diff --git a/oslo_config/validator.py b/oslo_config/validator.py
index 725a868..938ee65 100644
--- a/oslo_config/validator.py
+++ b/oslo_config/validator.py
@@ -22,6 +22,7 @@ project then it returns those errors.
 """
 
 import logging
+import re
 import sys
 
 try:
@@ -36,6 +37,11 @@ import yaml
 from oslo_config import cfg
 from oslo_config import generator
 
+VALIDATE_DEFAULTS_EXCLUSIONS = [
+    '.*_ur(i|l)', '.*connection', 'password', 'username', 'my_ip',
+    'host(name)?', 'glance_api_servers', 'osapi_volume_listen',
+    'osapi_compute_listen',
+]
 
 _validator_opts = [
     cfg.MultiStrOpt(
@@ -51,6 +57,16 @@ _validator_opts = [
         help='Path to a YAML file containing definitions of options, as '
              'output by the config generator.'),
     cfg.BoolOpt(
+        'check-defaults',
+        default=False,
+        help='Report differences between the sample values and current '
+             'values.'),
+    cfg.ListOpt(
+        'exclude-options',
+        default=VALIDATE_DEFAULTS_EXCLUSIONS,
+        help='Exclude options matching these patterns when comparing '
+             'the current and sample configurations.'),
+    cfg.BoolOpt(
         'fatal-warnings',
         default=False,
         help='Report failure if any warnings are found.'),
@@ -86,6 +102,73 @@ def _validate_deprecated_opt(group, option, opt_data):
     return option in name_data
 
 
+def _validate_defaults(sections, opt_data, conf):
+    """Compares the current and sample configuration and reports differences
+
+    :param section: ConfigParser instance
+    :param opt_data: machine readable data from the generator instance
+    :param conf: ConfigOpts instance
+    :returns: boolean wether or not warnings were reported
+    """
+    warnings = False
+    # Generating regex objects from ListOpt
+    exclusion_regexes = []
+    for pattern in conf.exclude_options:
+        exclusion_regexes.append(re.compile(pattern))
+    for group, opts in opt_data['options'].items():
+        if group in conf.exclude_group:
+            continue
+        if group not in sections:
+            logging.warning(
+                'Group %s from the sample config is not defined in '
+                'input-file', group)
+            continue
+        for opt in opts['opts']:
+            # We need to convert the defaults into a list to find
+            # intersections. defaults are only a list if they can
+            # be defined multiple times, but configparser only
+            # returns list
+            if not isinstance(opt['default'], list):
+                defaults = [str(opt['default'])]
+            else:
+                defaults = opt['default']
+
+            # Apparently, there's multiple naming conventions for
+            # options, 'name' is mostly with hyphens, and 'dest'
+            # is represented with underscores.
+            opt_names = set([opt['name'], opt.get('dest')])
+            if not opt_names.intersection(sections[group]):
+                continue
+            try:
+                value = sections[group][opt['name']]
+                keyname = opt['name']
+            except KeyError:
+                value = sections[group][opt.get('dest')]
+                keyname = opt.get('dest')
+
+            if any(rex.fullmatch(keyname) for rex in exclusion_regexes):
+                logging.info(
+                    '%s/%s Ignoring option because it is part of the excluded '
+                    'patterns. This can be changed with the --exclude-options '
+                    'argument', group, keyname)
+                continue
+
+            if len(value) > 1:
+                logging.info(
+                    '%s/%s defined %s times', group, keyname, len(value))
+            if not opt['default']:
+                logging.warning(
+                    '%s/%s sample value is empty but input-file has %s',
+                    group, keyname, ", ".join(value))
+                warnings = True
+            elif not frozenset(defaults).intersection(value):
+                logging.warning(
+                    '%s/%s sample value %s is not in %s',
+                    group, keyname, defaults, value)
+                warnings = True
+    return warnings
+
+
 def _validate_opt(group, option, opt_data):
     if group not in opt_data['options']:
         return False
@@ -114,12 +197,14 @@ def _validate(conf):
     parser.parse()
     warnings = False
     errors = False
+    if conf.check_defaults:
+        warnings = _validate_defaults(sections, opt_data, conf)
     for section, options in sections.items():
         if section in conf.exclude_group:
             continue
         for option in options:
             if _validate_deprecated_opt(section, option, opt_data):
-                logging.warn('Deprecated opt %s/%s found', section, option)
+                logging.warning('Deprecated opt %s/%s found', section, option)
                 warnings = True
             elif not _validate_opt(section, option, opt_data):
                 if section in KNOWN_BAD_GROUPS:
@@ -129,7 +214,8 @@ def _validate(conf):
                                  'cannot be validated properly.',
                                  option, section)
                     continue
-                logging.error('%s/%s not found', section, option)
+                logging.error('%s/%s is not part of the sample config',
+                              section, option)
                 errors = True
     if errors or (warnings and conf.fatal_warnings):
         return 1
diff --git a/releasenotes/notes/add-HostDomain-implement-rfc1033-c985a3054f824e9d.yaml b/releasenotes/notes/add-HostDomain-implement-rfc1033-c985a3054f824e9d.yaml
new file mode 100644
index 0000000..1f8d153
--- /dev/null
+++ b/releasenotes/notes/add-HostDomain-implement-rfc1033-c985a3054f824e9d.yaml
@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    Add ``HostDomain`` to handle address with underscore. Underscore are
+    allowed in domain by RFC1033 [1][2][3].
+
+    - [1] https://www.ietf.org/rfc/rfc1912.txt
+    - [2] https://www.ietf.org/rfc/rfc1033.txt
+    - [3] http://domainkeys.sourceforge.net/underscore.html
diff --git a/releasenotes/notes/validator-check-defaults-e7b596a2fde781a8.yaml b/releasenotes/notes/validator-check-defaults-e7b596a2fde781a8.yaml
new file mode 100644
index 0000000..3fdbfe6
--- /dev/null
+++ b/releasenotes/notes/validator-check-defaults-e7b596a2fde781a8.yaml
@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Add a ``--check-defaults`` flag to ``oslo-config-validator``. When set,
+    ``oslo-config-validator`` will compare the ``input-file`` with the sample
+    generated configuration and flag any discrepancies. It also obeys the
+    standard ``--exclude-group`` and ``--fatal-warning`` options.
diff --git a/requirements.txt b/requirements.txt
index 9c1d5c3..58bd439 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,6 +7,6 @@ netaddr>=0.7.18 # BSD
 stevedore>=1.20.0 # Apache-2.0
 oslo.i18n>=3.15.3 # Apache-2.0
 rfc3986>=1.2.0 # Apache-2.0
-PyYAML>=3.12 # MIT
+PyYAML>=5.1 # MIT
 requests>=2.18.0 # Apache-2.0
 importlib_metadata>=1.7.0;python_version<'3.8' # Apache-2.0
diff --git a/tox.ini b/tox.ini
index 1bc8c37..88e81fe 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 minversion = 3.2.0
 distribute = False
-envlist = py37,pep8
+envlist = py3,pep8
 ignore_basepython_conflict = true
 
 [testenv]
@@ -22,13 +22,6 @@ commands =
   stestr run --suppress-attachments {posargs}
   stestr slowest
 
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/doc/requirements.txt
-
 [testenv:pep8]
 commands =
   pre-commit run -a
@@ -56,7 +49,7 @@ deps =
   -r{toxinidir}/doc/requirements.txt
 commands =
   rm -fr doc/build
-  sphinx-build -W --keep-going -b html doc/source doc/build/html {posargs}
+  sphinx-build -W --keep-going -b html -j auto doc/source doc/build/html {posargs}
 
 [testenv:mypy]
 commands =
@@ -72,7 +65,7 @@ whitelist_externals =
 deps = {[testenv:docs]deps}
 commands =
   rm -rf releasenotes/build
-  sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
+  sphinx-build -W --keep-going -b html -j auto releasenotes/source releasenotes/build/html {posargs}
 
 [hacking]
 import_exceptions = oslo_config._i18n