Open Stack

Greetings,

I would like to add a new filter based on the load averages.

This filter will use the command uptime and will provides an option to choice a
period between 1, 5, and 15 minutes and an option to choice the max load
average (a float between 0 and 1).

Why:
  During a scheduling it could be useful to exclude a host that have a too
heavy load and the command uptime (available in all linux system) 
can return a load average of the system in different periods.

About the implementation:
  Currently 'all' drivers (libvirt, xenapi, vmware) supports a method
get_host_uptime that returns the output of the command 'uptime'. We have to add
in compute/stats.py a new method calculate_loadavg() that returns based on the
output of driver.get_host_uptime() from compute/ressource_tracker.py a well
formatted tuple of load averages for each periods. We also need to update
api/openstack/compute/contrib/hypervisors.py to take care of this new
field.

  The implementation will be divided in several parts:
    * Add to host_manager the possibility to get the loads_averages
    * Implement the filter based on this new property
    * Implement the filter with a per-aggregate configuration

The blueprint: https://blueprints.launchpad.net/nova/+spec/filter-based-uptime

I will be happy to get any comments about this filter, perharps it is not implemented
yet because of something I didn't see or my thinking of the implementation is wrong.

PS: I have checked metrics and cpu_resource but It does not get an averages of the
system load or perhaps I have not understand all.

Thanks a lot,
s.