oslo.config/doc/source/generator.rst

oslo-config-generator

oslo-config-generator is a utility for generating sample config files. For example, to generate a sample config file for oslo.messaging you would run:

$> oslo-config-generator --namespace oslo.messaging > oslo.messaging.conf

This generated sample lists all of the available options, along with their help string, type, deprecated aliases and defaults.

To generate a sample config file for an application myapp that has its own options and uses oslo.messaging, you can list both namespaces:

$> oslo-config-generator --namespace myapp --namespace oslo.messaging > myapp.conf

1.4

Defining Option Discovery Entry Points

The --namespace option specifies an entry point name registered under the 'oslo.config.opts' entry point namespace. For example, in oslo.messaging's setup.cfg we have:

[entry_points]
oslo.config.opts =
    oslo.messaging = oslo.messaging.opts:list_opts

The callable referenced by the entry point should take no arguments and return a list of (group, [opt_1, opt_2]) tuples, where group is either a group name as a string or an OptGroup object. Passing the OptGroup object allows the consumer of the list_opts method to access and publish group help. An example, using both styles:

opts1 = [
    cfg.StrOpt('foo'),
    cfg.StrOpt('bar'),
]

opts2 = [
    cfg.StrOpt('baz'),
]

baz_group = cfg.OptGroup(name='baz_group'
                         title='Baz group options',
                         help='Baz group help text')
cfg.CONF.register_group(baz_group)

cfg.CONF.register_opts(opts1, group='blaa')
cfg.CONF.register_opts(opts2, group=baz_group)

def list_opts():
    # Allows the generation of the help text for
    # the baz_group OptGroup object. No help
    # text is generated for the 'blaa' group.
    return [('blaa', opts1), (baz_group, opts2)]

Note

You should return the original options, not a copy, because the default update hooks depend on the original option object being returned.

The module holding the entry point must be importable, even if the dependencies of that module are not installed. For example, driver modules that define options but have optional dependencies on third-party modules must still be importable if those modules are not installed. To accomplish this, the optional dependency can either be imported using oslo.utils.importutils.try_import or the option definitions can be placed in a file that does not try to import the optional dependency.

Modifying Defaults from Other Namespaces

Occasionally applications need to override the defaults for options defined in libraries. At runtime this is done using an API within the library. Since the config generator cannot guarantee the order in which namespaces will be imported, we can't ensure that application code can change the option defaults before the generator loads the options from a library. Instead, a separate optional processing hook is provided for applications to register a function to update default values after all options are loaded.

The hooks are registered in a separate entry point namespace (oslo.config.opts.defaults), using the same entry point name as the application's list_opts() function.

[entry_points]
oslo.config.opts.defaults =
    keystone = keystone.common.config:update_opt_defaults

Warning

Never, under any circumstances, register an entry point using a name owned by another project. Doing so causes unexpected interplay between projects within the config generator and will result in failure to generate the configuration file or invalid values showing in the sample.

In this case, the name of the entry point for the default override function must match the name of one of the entry points defining options for the application in order to be detected and used. Applications that have multple list_opts functions should use one that is present in the inputs for the config generator where the changed defaults need to appear. For example, if an application defines foo.api to list the API-related options, and needs to override the defaults in the oslo.middleware.cors library, the application should register foo.api under oslo.config.opts.defaults and point to a function within the application code space that changes the defaults for oslo.middleware.cors.

The update function should take no arguments. It should invoke the public set_defaults functions in any libraries for which it has option defaults to override, just as the application does during its normal startup process.

from oslo_log import log

def update_opt_defaults():
    log.set_defaults(
        default_log_levels=log.get_default_log_levels() + ['noisy=WARN'],
    )

Generating Multiple Sample Configs

A single codebase might have multiple programs, each of which use a subset of the total set of options registered by the codebase. In that case, you can register multiple entry points:

[entry_points]
oslo.config.opts =
    nova.common = nova.config:list_common_opts
    nova.api = nova.config:list_api_opts
    nova.compute = nova.config:list_compute_opts

and generate a config file specific to each program:

$> oslo-config-generator --namespace oslo.messaging \
                         --namespace nova.common \
                         --namespace nova.api > nova-api.conf
$> oslo-config-generator --namespace oslo.messaging \
                         --namespace nova.common \
                         --namespace nova.compute > nova-compute.conf

To make this more convenient, you can use config files to describe your config files:

$> cat > config-generator/api.conf <<EOF
[DEFAULT]
output_file = etc/nova/nova-api.conf
namespace = oslo.messaging
namespace = nova.common
namespace = nova.api
EOF
$> cat > config-generator/compute.conf <<EOF
[DEFAULT]
output_file = etc/nova/nova-compute.conf
namespace = oslo.messaging
namespace = nova.common
namespace = nova.compute
EOF
$> oslo-config-generator --config-file config-generator/api.conf
$> oslo-config-generator --config-file config-generator/compute.conf

Sample Default Values

The default runtime values of configuration options are not always the most suitable values to include in sample config files - for example, rather than including the IP address or hostname of the machine where the config file was generated, you might want to include something like '10.0.0.1'. To facilitate this, options can be supplied with a 'sample_default' attribute:

cfg.StrOpt('base_dir'
           default=os.getcwd(),
           sample_default='/usr/lib/myapp')

API

oslo_config.generator

main

generate

register_cli_opts