Open Stack

Nova has had this long-standing known performance issue if you're 
filtering a large number of instances by IP. The instance IPs are stored 
in a JSON blob in the database so we don't do filtering in SQL. We pull 
the instances out of the database, deserialize the JSON and then apply a 
regex filter match in the nova-api python code.

At the Queens PTG we talked about possible ways to fix this and came up 
with this nova spec:

https://specs.openstack.org/openstack/nova-specs/specs/queens/approved/improve-filter-instances-by-ip-performance.html

The idea is to have nova get ports from neutron and apply the IP filter 
in neutron to whittle down the ports, then from that list of ports get 
the instances to pull out of the nova database.

One issue that has come up with this is neutron does not currently 
support regex filters when listing ports. There is an RFE for adding that:

https://bugs.launchpad.net/neutron/+bug/1718605

The proposed neutron implementation is to just do SQL LIKE substring 
matching in the database.

However, one issue that has come up is that the compute API accepts a 
python regex filter and uses re.match():

https://github.com/openstack/nova/blob/16.0.0/nova/compute/api.py#L2469

At least one good thing about that is match() only matches from the 
beginning of the string unlike search().

So for example I can filter on "192.16.*[1-5]$" if I wanted to, but 
that's not going to work with just a LIKE substring filter in SQL.

The question is, does anyone actually do more than basic substring 
matching with the IP filter today? Because if we started using neutron, 
that behavior would be broken. We've never actually documented the match 
restrictions on the IP filter, but that's not a good reason to break it.

One option is to make this configurable such that deployments which rely 
on the complicated pattern matching can just use the existing nova code 
despite performance issues. However, that's not interoperable, I hate 
config-driven API behavior, and it would mean maintaining two code paths 
in nova, which is also terrible.

I was trying to think of a way to determine if the IP filter passed to 
nova is basic or a complicated pattern match and let us decide that way, 
but I'm not sure if there are good ways to detect that - maybe by simply 
looking for special characters like (, ), - and $? But then there is [] 
and we have an IPv6 filter, so that gets messy too...

For now I'd just like to know if people rely on the regex match or not. 
Other ideas on how to handle this are appreciated.

-- 

Thanks,

Matt