deb-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

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_name, [opt_1, opt_2]) tuples. For example:

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

cfg.CONF.register_opts(opts, group='blaa')

def list_opts():
    return [('blaa', opts)]

You might choose to return a copy of the options so that the return value can't be modified for nefarious purposes, though this is not strictly necessary:

def list_opts():
    return [('blaa', copy.deepcopy(opts))]

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.

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