The cfg Module

Configuration options which may be set on the command line or in config files.

The schema for each option is defined using the Opt sub-classes, e.g.:

common_opts = [
    cfg.StrOpt('bind_host',
               default='0.0.0.0',
               help='IP address to listen on'),
    cfg.IntOpt('bind_port',
               default=9292,
               help='Port number to listen on')
]

Options can be strings, integers, floats, booleans, lists, or ‘multi strings’ or ‘key/value pairs’ (dictionary)

enabled_apis_opt = cfg.ListOpt('enabled_apis',
                               default=['ec2', 'osapi_compute'],
                               help='List of APIs to enable by default')

DEFAULT_EXTENSIONS = [
    'nova.api.openstack.compute.contrib.standard_extensions'
]
osapi_compute_extension_opt = cfg.MultiStrOpt('osapi_compute_extension',
                                              default=DEFAULT_EXTENSIONS)

Option schemas are registered with the config manager at runtime, but before the option is referenced:

class ExtensionManager(object):

    enabled_apis_opt = cfg.ListOpt(...)

    def __init__(self, conf):
        self.conf = conf
        self.conf.register_opt(enabled_apis_opt)
        ...

    def _load_extensions(self):
        for ext_factory in self.conf.osapi_compute_extension:
            ....

A common usage pattern is for each option schema to be defined in the module or class which uses the option:

opts = ...

def add_common_opts(conf):
    conf.register_opts(opts)

def get_bind_host(conf):
    return conf.bind_host

def get_bind_port(conf):
    return conf.bind_port

An option may optionally be made available via the command line. Such options must be registered with the config manager before the command line is parsed (for the purposes of –help and CLI arg validation):

cli_opts = [
    cfg.BoolOpt('verbose',
                short='v',
                default=False,
                help='Print more verbose output'),
    cfg.BoolOpt('debug',
                short='d',
                default=False,
                help='Print debugging output'),
]

def add_common_opts(conf):
    conf.register_cli_opts(cli_opts)

The config manager has two CLI options defined by default, –config-file and –config-dir:

class ConfigOpts(object):

    def __call__(self, ...):

        opts = [
            MultiStrOpt('config-file',
                    ...),
            StrOpt('config-dir',
                   ...),
        ]

        self.register_cli_opts(opts)

Option values are parsed from any supplied config files using oslo.config.iniparser. If none are specified, a default set is used e.g. glance-api.conf and glance-common.conf:

glance-api.conf:
  [DEFAULT]
  bind_port = 9292

glance-common.conf:
  [DEFAULT]
  bind_host = 0.0.0.0

Option values in config files override those on the command line. Config files are parsed in order, with values in later files overriding those in earlier files.

The parsing of CLI args and config files is initiated by invoking the config manager e.g.:

conf = ConfigOpts()
conf.register_opt(BoolOpt('verbose', ...))
conf(sys.argv[1:])
if conf.verbose:
    ...

Options can be registered as belonging to a group:

rabbit_group = cfg.OptGroup(name='rabbit',
                            title='RabbitMQ options')

rabbit_host_opt = cfg.StrOpt('host',
                             default='localhost',
                             help='IP/hostname to listen on'),
rabbit_port_opt = cfg.IntOpt('port',
                             default=5672,
                             help='Port number to listen on')

def register_rabbit_opts(conf):
    conf.register_group(rabbit_group)
    # options can be registered under a group in either of these ways:
    conf.register_opt(rabbit_host_opt, group=rabbit_group)
    conf.register_opt(rabbit_port_opt, group='rabbit')

If no group attributes are required other than the group name, the group need not be explicitly registered e.g.

def register_rabbit_opts(conf):

# The group will automatically be created, equivalent calling:: # conf.register_group(OptGroup(name=’rabbit’)) conf.register_opt(rabbit_port_opt, group=’rabbit’)

If no group is specified, options belong to the ‘DEFAULT’ section of config files:

glance-api.conf:
  [DEFAULT]
  bind_port = 9292
  ...

  [rabbit]
  host = localhost
  port = 5672
  use_ssl = False
  userid = guest
  password = guest
  virtual_host = /

Command-line options in a group are automatically prefixed with the group name:

--rabbit-host localhost --rabbit-port 9999

Option values in the default group are referenced as attributes/properties on the config manager; groups are also attributes on the config manager, with attributes for each of the options associated with the group:

server.start(app, conf.bind_port, conf.bind_host, conf)

self.connection = kombu.connection.BrokerConnection(
    hostname=conf.rabbit.host,
    port=conf.rabbit.port,
    ...)

Option values may reference other values using PEP 292 string substitution:

opts = [
    cfg.StrOpt('state_path',
               default=os.path.join(os.path.dirname(__file__), '../'),
               help='Top-level directory for maintaining nova state'),
    cfg.StrOpt('sqlite_db',
               default='nova.sqlite',
               help='file name for sqlite'),
    cfg.StrOpt('sql_connection',
               default='sqlite:///$state_path/$sqlite_db',
               help='connection string for sql database'),
]

Note that interpolation can be avoided by using ‘$$’.

Options may be declared as required so that an error is raised if the user does not supply a value for the option.

Options may be declared as secret so that their values are not leaked into log files:

opts = [
   cfg.StrOpt('s3_store_access_key', secret=True),
   cfg.StrOpt('s3_store_secret_key', secret=True),
   ...
]

This module also contains a global instance of the ConfigOpts class in order to support a common usage pattern in OpenStack:

from oslo.config import cfg

opts = [
    cfg.StrOpt('bind_host', default='0.0.0.0'),
    cfg.IntOpt('bind_port', default=9292),
]

CONF = cfg.CONF
CONF.register_opts(opts)

def start(server, app):
    server.start(app, CONF.bind_port, CONF.bind_host)

Positional command line arguments are supported via a ‘positional’ Opt constructor argument:

>>> conf = ConfigOpts()
>>> conf.register_cli_opt(MultiStrOpt('bar', positional=True))
True
>>> conf(['a', 'b'])
>>> conf.bar
['a', 'b']

It is also possible to use argparse “sub-parsers” to parse additional command line arguments using the SubCommandOpt class:

>>> def add_parsers(subparsers):
...     list_action = subparsers.add_parser('list')
...     list_action.add_argument('id')
...
>>> conf = ConfigOpts()
>>> conf.register_cli_opt(SubCommandOpt('action', handler=add_parsers))
True
>>> conf(args=['list', '10'])
>>> conf.action.name, conf.action.id
('list', '10')