Hi folks, while trying to reproduce this behaviour myself I think i've
stumbled upon some interesting behaviour. I setup a test as follows and
checked for errors at specific points. I have a 4 node setup (24
core/64G ram) with 3 gateways and 1 compute. Neutron is configured with
l3_ha enabled and max_agents_per_router set to 3;
stage 1: created two projects with 1 router each (which gives two sets
of keepalived each with the same VR_ID (1)) and checked keepalived logs
- system load is minimal, no re-elections observed post-create.
stage 2: scaled horizontally to 200 projects each with 1 router (giving
200 routers with VR_ID 1 each within their own network). system load is
minimal, no re-elections observed post-create, observed that all master
state routers are on the same host.
stage 3: scaled one project vertically by creating 200 routers within
same project. As i started to get into the VR_70s i started to see some
of the extant routers get re-elected e.g. "VRRP_Instance(VR_76) Received
higher prio advert". If i run a tcpdump on one of my ha- interfaces
inside a qrouter- namespace I see a flood of "VRRPv2, Advertisement"
with each VR_ID being advertised every 2s from the current master (as
expected since that's the default interval in neutron). The consequence
of this is that neutron is frequently having to cathup with keepalived
(by running neutron-keepalived-state-change) which causes more traffic
and all without cause since there is no need for these failovers to be
Since the advert interval is configurable in neutron  I am going to
go ahead and try changing it to see of that can stop these re-elections
but that seems a little hacky as a fix so just wondering if there's
another way to mitigate these effects. I need to double check the vrrp
spec but iirc since these advertisements are sent out by the master, if
the master dies it would affect how long it takes for a re-election to
occur (spec says "(3 * Advertisement_Interval) + Skew_time") and during
that time VMs would be unreachable so maybe there's another way.
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Neutron integrated with OpenVSwitch drops packets and fails to
plug/unplug interfaces from OVS on router interfaces at scale
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