Open Stack

Hi,

We've started implementing gnocchi support in CloudKitty. But we're
facing some issues. Some problems where client sided and are now fixed,
but for some others it might doing wrong requests or not using gnocchi's
full potential.

Here are some problems we're actually facing:

We can't directly query gnocchi resource indexer for a specific resource
revision. Let me explain it, if you want to search for every instances
active for a specific timeframe you'll get a result but the revision
will be the latest, even if it's after the timeframe you requested. If
you add resource revision to the request you'll get an empty request if
it doesn't match the latest version. We can't add history to the request
as we'll have more than one response when we only need latest revision
for the timeframe. One workaround is to first do a request to query
every active instance and then do a query for every instance with
history filtering on UUID and revision and limiting to one result. It's
suboptimal as it requires many requests to get the correct information.


The other problem we are having is when requesting measures. Let me
first tell you how CloudKitty is collecting data to set the context.
We've got a collection period (default 3600 seconds), every period we
query the backend for a specific timeframe (start = last collection,
stop = last + period). If we're missing data we restart from where we
stopped, which can be pretty far in the past.
We're using gnocchi as ceilometer's storage and by default it's pretty
hard to exploit data stored. If we request data too far in the past that
is using a higher granularity than our collection period then we got an
empty dataset from gnocchi. It's pretty ambiguous as we don't know if
it's because there is no data, or because our timeframe is too short.
That means we need to query for the archive policy and find what should
be the minimum granularity for the period. In some way it's normal to no
get data because gnocchi is unable to provide accurate data for this
period, but at least get information that we are requesting too
precisely. Or send us the data, since we've got the timestamp and
the granularity, we can easily detect that the result is not accurate
and decide what we should do.

Sorry for the wall of text, and thanks to people that took time to read
it.

BTW, we're available in #cloudkitty channel. You can reach me on most
openstack channels too, I'm in UTC+1 timezone.

Hoping we can find a solution and ship gnocchi support in the next
CloudKitty version, which is pretty much ready.

Cheers
----
Stéphane Albert   -  05 82 95 65 36
Objectif Libre  www.objectif-libre.com
Infrastructure et Formations Linux