ceilometer is heavily depends on python stevedore, you can take a look at stevedore first here http://stevedore.readthedocs.org/en/l...

Then just select the right agent base PollAgent, NotificationAgent, CentralAgent ,Evaluator as your base class then check the official example here http://docs.openstack.org/developer/c... to write your custom plugins.

Note: you have to register your custom plugin in stevedore entry_point.txt and restart the ceilometer service to make it work.

ceilometer.alarm.evaluator =
    threshold = ceilometer.alarm.evaluator.threshold:ThresholdEvaluator
    combination = ceilometer.alarm.evaluator.combination:CombinationEvaluator


ceilometer.alarm.evaluator_service =
    default = ceilometer.alarm.service:AlarmEvaluationService
    singleton = ceilometer.alarm.service:SingletonAlarmService
    partitioned = ceilometer.alarm.service:PartitionedAlarmService
    # NOTE(sileht): for backward compatibility
    ceilometer.alarm.service.SingletonAlarmService = ceilometer.alarm.service:SingletonAlarmService
    **your_customized_plugin_alias=your_customized_plugin_name.namespace:your_customized_plugin**

Hope that helps!

Vic