[ovs-dev] [PATCH 1/2] ovn-controller: Datapath based conntrack zone for load-balancing.

[Ben Pfaff]

On Tue, Aug 30, 2016 at 01:42:06PM -0700, Guru Shetty wrote:
> On 30 August 2016 at 13:03, Ben Pfaff <blp at ovn.org> wrote:
> 
> > On Tue, Aug 23, 2016 at 02:46:17AM -0700, Gurucharan Shetty wrote:
> > > Currently ct_lb() logical action is only added for a logical switch and
> > > we use the conntrack zone allocated for the logical port.  A future
> > commit
> > > will use ct_lb() for a logical router too.  In that case, use the
> > allocated
> > > DNAT zone.
> > >
> > > Signed-off-by: Gurucharan Shetty <guru at ovn.org>
> >
> > Can you help me to understand why the desired behavior is different in
> > each of these cases?
> >
> 
> Currently we do the following conntrack zone allocations.
> 1. A conntrack zone for each logical port. This has to be unique only per
> hypervisor. We use this zone to do both firewall and east-west
> load-balancing.
> 
> For firewall, we send the packet to conntrack to defragment it and track it
> and figure out whether it is invalid, new, established etc. Invalid packets
> are dropped. new connections are committed.
> 
> For load-balancing, defragmented packets are DNATed into one of the
> possible endpoints. We do the load-balancing at the endpoint (instead of
> say in a router) because of the asymmetric  nature of OVN router pipeline
> handling for east-west.
> So when we see ct_lb() action on a switch, we can just use the conntrack
> zone allocated for that logical port.
> 
> 
> 2. Two conntrack zones per gateway router.
> A gateway router only resides in a particular chassis. We have one
> conntrack zone for DNAT and another for SNAT.
> 
> Now when I want to add ct_lb() action for the gateway router, I want to use
> it as part of the gateway router pipeline. Since load-balancing is nothing
> but a DNAT using one of the chosen endpoint, the conntrack zone has to be a
> DNAT zone allocated to that gateway router.
> 
> Did I give the answer to your question? Or was it something else that you
> were looking an explanation for?

One underlying question I'm trying to understand is whether this
difference is something inherent in the definition of logical switches
and logical routers, and thus the approach taken here of automatically
choosing a strategy is appropriate, or whether this is just what we
happen to be doing now, in which case it might be better to make how to
select the zone a parameter to ct_lb.