OVN is configured as a collection of logical switches and routers connected together. These logical entities get compiled into logical flows and then later into hypervisor-specific OpenFlow flows. By the time that it is deployed, the original logical entities are far removed from what the actual network traffic hits. An administrator can currently look at individual flows to determine where traffic is going, but it's difficult to tie these back to the logical entities that were originally created. For this task, we want to be able to have centralized query-able statistics for OVN logical entities. For instance, knowing how many packets a certain switch/router has seen, how many packets were dropped by a certain switch/router, how many packets are going over specific routes, etc.
Another, maybe a bit indirect, way of getting statistics for given entities is to use IPFIX and allow the CMS to define different observation ids for different entities. Something similar was requested a while back upstream: https://mail.openvswitch.org/pipermail/ovs-dev/2016-September/323660.html And Adrian's series to add drop counters is also related as it adds an OVN "sample" action: https://www.mail-archive.com/ovs-dev@openvswitch.org/msg66608.html https://patchwork.ozlabs.org/project/ovn/list/?series=304578&state=*
I am closing this issue. There is a new effort underway between the OVN team and Prometheus team to get data exported. The new effort supersedes this old issue.