Developing For Bcfg2

While the Bcfg2 server provides a good interface for representing general system configurations, its plugin interface offers the ability to implement configuration interfaces and representation tailored to problems encountered by a particular site. This chapter describes what plugins are good for, what they can do, and how to implement them.

Bcfg2 Plugins

Bcfg2 plugins are loadable python modules that the Bcfg2 server loads at initialization time. These plugins can contribute to the functions already offered by the Bcfg2 server or can extend its functionality. In general, plugins will provide some portion of the configuration for clients, with a data representation that is tuned for a set of common tasks. Much of the core functionality of Bcfg2 is implemented by several plugins, however, they are not special in any way; new plugins could easily supplant one or all of them.

The following table describes the various functions of bcfg2 plugins.

|| ‘’ ‘’‘Name’‘’ ‘’ || ‘’ ‘’‘Description’‘’ ‘’ || || Probes || Plugins can issue commands to collect client-side state (like hardware inventory) to include in client configurations || || !ConfigurationEntry List || Plugins can construct a list of per-client configuration entry lists to include in client configurations. || || !ConfigurationEntry contents || Literal values for configuration entries. || || XML-RPC functions || Plugins can export function calls that expose internal functions. ||

Writing Bcfg2 Plugins

Bcfg2 plugins are python classes that subclass from Bcfg2.Server.Plugin.Plugin. Several plugin-specific values must be set in the new plugin. These values dictate how the new plugin will behave with respect to the above four functions. The following table describes all important member fields.

|| ‘’ ‘’‘Name’‘’ ‘’ || ‘’ ‘’‘Description’‘’ ‘’ || ‘’ ‘’‘Format’‘’ ‘’ || || __name__ || The name of the plugin || string || || __version__ || The plugin version (generally tied to revctl keyword expansion). || string || || __author__ || The plugin author. || string || || __rmi__ || Set of functions to be exposed as XML-RPC functions || List of function names (strings) || || Entries || Multidimentional dictionary of keys that point to the function [[BR]] used to bind literal contents for a given configuration entity. || Dictionary of !ConfigurationEntityType, Name keys and function reference values || || !BuildStructures || Function that returns a list of the structures for a given client || Member function || || !GetProbes || Function that returns a list of probes that a given client should execute || Member function || || !ReceiveData || Function that accepts the probe results for a given client. || Member function ||

Example Plugin

import Bcfg2.Server.Plugin
class MyPlugin(Bcfg2.Server.Plugin.Plugin):
   '''An example plugin'''
   # All plugins need to subclass Bcfg2.Server.Plugin.Plugin
   __name__ = 'MyPlugin'
   __version__ = '1'
   __author__ = 'me@me.com'
   __rmi__ = ['myfunction']
   # myfunction is not available remotely as MyPlugin.myfunction

   def __init__(self, core, datastore):
       Bcfg2.Server.Plugin.Plugin.__init__(self, core, datastore)
       self.Entries = {'Path':{'/etc/foo.conf': self.buildFoo}}

   def myfunction(self):
       '''function for xmlrpc rmi call'''
       #do something
       return True

   def buildFoo(self, entry, metadata):
       '''Bind per-client information into entry based on metadata'''
       entry.attrib.update({'type':'file', 'owner':'root', 'group':'root', 'perms':'644'})
       entry.text = '''contents of foo.conf'''

Example Connector

import Bcfg2.Server.Plugin

class Foo(Bcfg2.Server.Plugin.Plugin,
         Bcfg2.Server.Plugin.Connector):
    '''The Foo plugin is here to illustrate a barebones connector'''
    name = 'Foo'
    version = '$Revision: $'
    experimental = True

    def __init__(self, core, datastore):
        Bcfg2.Server.Plugin.Plugin.__init__(self, core, datastore)
    Bcfg2.Server.Plugin.Connector.__init__(self)
        self.store = XMLFileBacked(self.data, core.fam)

    def get_additional_data(self, metadata):
        mydata = {}
        for data in self.store.entries['foo.xml'].data.get("foo", []):
            mydata[data] = "bar"
        return  dict([('mydata', mydata)])

    def get_additional_groups(self, meta):
        return self.cgroups.get(meta.hostname, list())