tcollector is a framework to collect data points and store them in OpenTSDB. It allows you to write simple collectors that it'll run and monitor. It also handles the communication with the TSDs.

For more info, see

http://www.opentsdb.net/tcollector.html

Additionally, this repositary contains collector libvirt_vm, which collects data about virtual machine host and virtual machines running on the host (via libvirt). List of metrices collector provides are available in collector's source code.