The Ceilometer project maintains a list of things that need to be worked on at: http://wiki.openstack.org/EfficientMetering/RoadMap but feel free to work on something else.
Ceilometer’s architecture is based heavily on the use of plugins to make it easy to extend to collect new sorts of data or store them in different databases.
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The core parts of ceilometer, not separated into a plugin, are fairly simple but depend on code that is part of nova right now. One project goal is to move the rest of those dependencies out of nova and into openstack-common. Logging and RPC are already done, but the service and manager base classes still need to move.
The first version of ceilometer has extensive unit tests, but has not seen much run-time in real environments. Setting up a copy of ceilometer to monitor a real OpenStack installation or to perform some load testing would be especially helpful.
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