[Bug 1749425] [NEW] Neutron integrated with OpenVSwitch drops packets and fails to plug/unplug interfaces from OVS on router interfaces at scale

[James Hebden]

Public bug reported:

Description:    Ubuntu 16.04.3 LTS
Release:        16.04
Linux 4.4.0-96-generic on AMD64
Neutron 2:10.0.4-0ubuntu2~cloud0 from Cloud Archive xenial-updates/ocata
OpenVSwitch 2.6.1-0ubuntu5.2~cloud0 from Cloud Archive xenial-upates/ocata

In an environment with three bare-metal Neutron deployments, hosting
upward of 300 routers, with approximately the same number of instances,
typically one router per instance, packet loss on instances accessed via
floating IPs, including complete connectivity loss, is experienced. The
problem is exacerbated by enabling L3HA, likely due to the increase in
router namespaces to be scheduled and managed, and the additional
scheduling work of bringing up keepalived and monitoring the keepalived
VIP.

Reducing the number of routers and rescheduling routers on new hosts,
causing the routers to undergo a full recreation of namespace, iptables
rules, and replugging of interfaces into OVS will correct packet loss or
connectivity loss on impacted routers.

On Neutron hosts in this environment, we have used systemtap to trace
calls to kfree_skb which reveals the majority of dropped packets occur
in the openvswitch module, notably on the br-int bridge. Inspecting the
state of OVS shows many qtap interfaces which are no longer present on
the Neutron host which are still plugged in to OVS.

Diagnostic outputs in following comments.

** Affects: neutron
     Importance: Undecided
         Status: New

** Affects: openvswitch (Ubuntu)
     Importance: Undecided
         Status: New

** Also affects: neutron
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1749425

Title:
  Neutron integrated with OpenVSwitch drops packets and fails to
  plug/unplug interfaces from OVS on router interfaces at scale

Status in neutron:
  New
Status in openvswitch package in Ubuntu:
  New

Bug description:
  Description:    Ubuntu 16.04.3 LTS
  Release:        16.04
  Linux 4.4.0-96-generic on AMD64
  Neutron 2:10.0.4-0ubuntu2~cloud0 from Cloud Archive xenial-updates/ocata
  OpenVSwitch 2.6.1-0ubuntu5.2~cloud0 from Cloud Archive xenial-upates/ocata

  In an environment with three bare-metal Neutron deployments, hosting
  upward of 300 routers, with approximately the same number of
  instances, typically one router per instance, packet loss on instances
  accessed via floating IPs, including complete connectivity loss, is
  experienced. The problem is exacerbated by enabling L3HA, likely due
  to the increase in router namespaces to be scheduled and managed, and
  the additional scheduling work of bringing up keepalived and
  monitoring the keepalived VIP.

  Reducing the number of routers and rescheduling routers on new hosts,
  causing the routers to undergo a full recreation of namespace,
  iptables rules, and replugging of interfaces into OVS will correct
  packet loss or connectivity loss on impacted routers.

  On Neutron hosts in this environment, we have used systemtap to trace
  calls to kfree_skb which reveals the majority of dropped packets occur
  in the openvswitch module, notably on the br-int bridge. Inspecting
  the state of OVS shows many qtap interfaces which are no longer
  present on the Neutron host which are still plugged in to OVS.

  Diagnostic outputs in following comments.

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