Trove/DynamicExtensionLoading

Description

The current trove impl for loading API extensions is based on a single path which is specified in the trove conf file and then searched at trove-api start-up time to find and load extensions. While this approach is sufficient for loading trove proper extensions it becomes more painful for consumers who wish to package and / or consume trove extensions not shipped with trove proper. With the current approach, a consumer must copy his / her extension class (a concrete impl of trove.common.extensions.ExtensionDescriptor [1]) into the path specified by the api_extensions_path conf property[2] in trove.conf in order for it to be picked up the the trove-api extension loading [3]. The act of copying py files into another modules install path is a bad practice and this is not a very robust / flexible approach.

What's proposed here to move to a more dynamic means to discover and load extensions using the stevedore package: http://stevedore.readthedocs.org/en/latest/index.html

• [1] https://github.com/openstack/trove/blob/master/trove/openstack/common/extensions.py#L35
• [2] https://github.com/openstack/trove/blob/master/trove/common/cfg.py#L40
• [3] https://github.com/openstack/trove/blob/master/trove/openstack/common/extensions.py#L407

Justification/Benefits

A more dynamic / robust means to discover trove extensions will allow more accessible

Impacts

Configuration

• Does this impact any configuration files? If so, which ones?

Database

• Does this impact any existing tables? If so, which ones?
• Are the changes forward and backward compatible?
• Be sure to include the expected migration process

Public API

• Does this change any API that an end-user has access to?
• Are there any exceptions in terms of consistency with other APIs?

CLI interface

• How the command will look like?
• Does it extends the already existed command interfaces ?

ReST Part

• Which HTTP methods added ?
• Which routes were added/modified/extended?
• How does the Request body look like?
• How does the Response object look like?

Internal API

• Does this change any internal messages between API and Task Manager or Task Manager to Guest

RPC API description

• Method name.
• Method parameters.
• Message type (cast/call).

Guest Agent

• Does this change behavior on the Guest Agent? If so, is it backwards compatible with API and Task Manager?