Michael McCune d768fbc97d refactoring castellan configuration

This change adds a module for listing configuration options and setting
their defaults. It also changes the key manager base class to
incorporate a configuration during creation. By default, the key manager
will continue to use the global CONF object from the oslo.config
package.

For the most part, this change will be backwards compatible. The one
exception is the creation of sample configuration files. Previously,
importing castellan was sufficient to add these options to the global
configuration object. Now, these options will need to be applied by
using the castellan.options.list_opts function, or adding them through
other means, to create sample configuration files. Similar applies for
setting configuration before instantiating a key manager.

changes
* adding castellan.options with list_opts and set_defaults functions
* changing KeyManager abc to include a configuration option to __init__
* changing barbican and not_implemented key managers to accept
  configuration parameters
* adding tests for set_defaults function
* fixing barbican tests to accomodate new configuration parameter
* adding documentation about configuration usage
* adding castellan configs to oslo entry point in setup.cfg
* adding a genconfig target to tox for producing a sample castellan
  configuration file
* adding the sample configuration file to the git ignore
* renaming barbican option api_version to barbican_api_version

Change-Id: I86d6d7d49a893beaae6f311060ec593e0482d889
Implements: blueprint improved-configuration-options

2015-08-12 12:03:36 -04:00

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Usage

To use castellan in a project:

import castellan

Configuring castellan

Castellan contains several options which control the key management service usage and the configuration of that service. It also contains functions to help configure the defaults and produce listings for use with the oslo-config-generator application.

In general, castellan configuration is handled by passing an oslo_config.cfg.ConfigOpts object into the castellan.key_manager.API call when creating your key manager. By default, when no ConfigOpts object is provided, the key manager will use the global oslo_config.cfg.CONF object.

Example. Using the global CONF object for configuration.

from castellan import key_manager

manager = key_manager.API()

Example. Using a predetermined configuration object.

from oslo_config import cfg
from castellan import key_manager

conf = cfg.ConfigOpts()
manager = key_manager.API(configuration=conf)

Controlling default options

To change the default behavior of castellan, and the key management service it uses, the castellan.options module provides the set_defaults function. This function can be used at run-time to change the behavior of the library or the key management service provider.

Example. Changing the barbican endpoint.

from oslo_config import cfg
from castellan import options
from castellan import key_manager

conf = cfg.ConfigOpts()
options.set_defaults(conf, barbican_endpoint='http://192.168.0.1:9311/')
manager = key_manager.API(conf)

Example. Changing the key manager provider while using the global configuration.

from oslo_config import cfg
from castellan import options
from castellan import key_manager

options.set_defaults(cfg.CONF, api_class='some.other.KeyManager')
manager = key_manager.API()

Generating sample configuration files

Castellan includes a tox configuration for creating a sample configuration file. This file will contain only the values that will be used by castellan. To produce this file, run the following command from the root of the castellan project directory:

$ tox -e genconfig

Adding castellan to configuration files

One common task for OpenStack projects is to create project configuration files. Castellan provides a list_opts function in the castellan.options module to aid in generating these files when using the oslo-config-generator. This function can be specified in the setup.cfg file of your project to inform oslo of the configuration options. Note, this will use the default values supplied by the castellan package.

Example. Adding castellan to the oslo.config entry point.

[entry_points]
oslo.config.opts =
    castellan.config = castellan.options:list_opts

For more information on the oslo configuration generator, please see http://docs.openstack.org/developer/oslo.config/generator.html

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