[ovs-discuss] OVS deleting flows from the datapath on exit

Ben Pfaff blp at ovn.org
Fri Nov 1 20:35:07 UTC 2019

OVS currently can gracefully exit in two ways: either with or without
deleting the datapath.  But, either way, it deletes all of the flows
from the datapath before it exits.  That is due to commit e96a5c24e853
("upcall: Remove datapath flows when setting n-threads."), which was
first released in OVS 2.1 back in 2014.

This isn't usually a big deal.  However, some controller folks I'm
talking to are concerned about upgrade.  If the datapath flows persisted
after OVS exits, then existing network connections (and perhaps some
that are "similar" to them because they match the same megaflows) could
carry on while the upgrade was in progress.  

I am surprised that I have not heard complaints about this in the 5
years that the behavior has been this way.  Does anyone have any stories
to report about it now that I bring it up?  Contrariwise, if we changed
OVS so that it did not delete datapath flows on exit, can anyone suggest
what problems that might cause?



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