http://docs.openstack.org/developer/ceilometer/
https://www.rdoproject.org/CeilometerQuickStart
Ceilometer Workflow :
Collect -> (Optionally) Transform -> Publish -> Store -> Read
Telemetery meter types
Cumulative(누적) - Increasing over time (instance hours)
Delta - Changing over time (bandwidth)
Gauge - Discrete items (floating IPs, image uploads) and fluctuating values (disk I/O)
