Configuration File Deprecation Support

Launchpad blueprint

Allow the inifile (config file) providers to handle deprecated options. This should include cleaning up old deprecated names from config files and also allow using the deprecated name instead of the new name.

Problem description

When moving to new releases of OpenStack, config file options are frequently deprecated because they’re no longer needed, or they’ve been renamed.

After an upgrade this means that operators will frequently have the old and new config option in place, but the old option is no longer used or maintained.

Additionally, when upgrading it can be useful to update the Puppet modules before actually upgrading the service. A frequent problem when doing this is that the newer module only supports the new names for options instead of the older deprecated names.

Proposed change

Add additional parameters to the openstacklib inifile provider help manage cleanup removed and renamed configuration options. All inifile providers in other OpenStack Puppet modules that derive from this provider would inherit the new behavior. The syntax would allow specifying the old name for options which could be used to purge the old names or to use them in preference to the new names. For example:

cinder_config { 'oslo_logging/new_option':
  deprecated_name => 'DEFAULT/old_option_name',
  value           => $value,
}

In this case, it would populate the oslo_logging/new_option key in the Cinder config file with the contents of $value as normally expected. However, it would also purge the old name DEFAULT/old_option_name as given by deprecated_name.

The following new parameters would be supported:

deprecated_name
This is a string or array of old names that have been deprecated. Array should be supported because there are sometimes multiple names that have been deprecated in a single release. Defaults to an empty array.
purge_deprecated
If true, and if use_deprecated is false, then any deprecated_name values provided will be treated as if they had been specified separately with an ensure value of absent. Defaults to true.
use_deprecated
If true, then the inifile provider will act as if additional resources of the same type were specified for each deprecated_name with the same value and ensure parameters. Defaults to false.

It’s expected that both use_deprecated and purge_deprecated would be set globally for each config provider as needed, either using resource defaults or resource collectors.

Alternatives

Currently the old deprecated options left behind cause no harm. We could ignore this issue. This has the downside that it is not clear which value is currently used.

The inifile provider could be set to purge unmanaged options. Currently we depend on distributions to provide a base configuration file. In the past there have been issues with the OpenStack Puppet modules not managing all required options and depending on values provided in the base configuration files. This approach would require testing all of the existing modules to ensure they manage all needed options and also changing acceptance tests to use the purge functionality to prevent regressions.

Data model impact

None

Module API impact

Everything has been already mentioned in Proposed change.

End user impact

None

Performance Impact

Potential implementations might create additional resources to ensure the deprecated config value state. This could increase the number of resources being managed and the Puppet catalog size.

A small amount of additional overhead may be incurred to find and remove the deprecated names.

Deployer impact

Existing configuration files with deprecated options would be removed as described. When this occurs, services will be restarted. Impact of this is expected to be minimal since most of these changes would occur between major releases of the modules. In that case, the deployer is expected to be upgrading services and restarting them already.

It is expected that deployers may set use_deprecated to true in preparation to for upgrades, allowing upgrading the Puppet modules in some cases before upgrading the services they manage.

Deployers that wish to disable the new behavior could set the purge_deprecated parameter to false.

Developer impact

Developers would need to populate the deprecated_names parameter when renaming configuration options.

Implementation

Assignee(s)

Primary assignee:
clayton-oneill (IRC nick clayton)

Work Items

  • Identify existing option with deprecation as test candidate
  • Create a unit rspec in openstacklib and child module
  • Create a functional test in openstacklib and child module
  • Add implementation to openstacklib inifile provider

Dependencies

None

Testing

Unit and functional should be added to ensure base functionality and prevent regressions.

Documentation Impact

Currently documentation of inifile providers is spotty. This may be an opportunity to move that documentation into the openstacklib module.

References

None