root/trunk/bcfg2/doc/plugin-roles

This documents available plugin roles. 

1) list of plugin roles

| Role          | Class              | Status |
|---------------+--------------------+--------|
| Metadata      | Metadata           | done   |
| Connector     | Connector          | done   |
| Probing       | Probing            | done   |
| Structure     | Structure          | done   |
| Structure Val | StructureValidator | done   |
| Generator     | Generator          | done   |
| Goals Val     | GoalValidator      | done   |
| Statistics    | Statistics         | done   |
| Pull Source   | PullSource         | done   |
| Pull Target   | PullTarget         | done   |
| Version       | Version            | started|
| Decision      | Decision           | done   |
| Remote        | Remote             | none   |
| Syncing       | Syncing            | none   |
|---------------+--------------------+--------|

2) Plugin Capabilities

* Metadata
** Initial metadata construction
** Connector data accumulation
** ClientMetadata instance delivery
** Introspection interface (for bcfg2-info & co)
* Connector
** Provide additional data for ClientMetadata instances 
* Probing
** send executable probes to clients and receive data responses
* Structure
** Produce a list of configuration entries that should be included in
   client configurations
** Each structure plugin is produces a list of structures
** Core verifies that each bundle listed has been constructed
* Structure Validation
** Validate a client entry list's internal consistency, modifying if needed
* Generator
* Goals Validation
** Validate client goals, modifying if needed
* Pull Source
** Plugin can provide entry information about clients
* Pull Target
** Plugin can accept entry data and merge it into the specification
* Version
** Plugin can read revision information from VCS of choice
** Will provide an interface for producing commits made by the
   bcfg2-server
* Decision

3) Configuration of plugins

Plugin configuration will be simplified substantially. Now, a single
list of plugins (including plugins of all capabilities) is specified
upon startup (either via bcfg2.conf or equivalent). This mechanism
replaces the current split configuration mechanism where generators,
structures, and other plugins are listed independently. Instead, all
plugins included in the startup list will be initialized, and each
will be enabled in all roles that it supports. This will remove a
current source of confusion and potential configuration errors,
wherein a plugin is enabled for an improper set of goals. (ie Cfg
enabled as a structure, etc) This does remove the possibility of
partially enabling a plugin for one of its roles without activating it
across the board, but I think this is a corner case, which will be
poorly supported by plugin implementers. If needed, this use case can
be explicitly supported by the plugin author, through use of a config
file directive. 

4) User Visible Changes

Connector data is added to ClientMetadata instances using the name of
the connector plugin. This means that the dictionary of key/val probe
pairs included with metadata is now available as metadata.Probes
(instead of metadata.probes). Once properties are available the same
way, they will likewise change names to metadata.Properties from their
current name. 

Plugin configuration will change. A single field "plugins" in
bcfg2.conf will supercede the combination of the "generators" and 
"structures" fields. 

Default loading of needed plugins is now explicit; this means that
Statistics (if used) should be listed in the plugins line of
bcfg2.conf. 

5) Notes
* Need to ensure bundle accumulation occurs with connector groups