[Bug 1894843] Re: [dvr_snat] Router update deletes rfp interface from qrouter even when VM port is present on this host

[Łukasz Zemczak]

Hello ITD27M01, or anyone else affected,

Accepted neutron into groovy-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/neutron/2:17.1.0-0ubuntu2 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
groovy to verification-done-groovy. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-groovy. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: neutron (Ubuntu Groovy)
       Status: Triaged => Fix Committed

** Tags added: verification-needed verification-needed-groovy

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https://bugs.launchpad.net/bugs/1894843

Title:
  [dvr_snat] Router update deletes rfp interface from qrouter even when
  VM port is present on this host

Status in Ubuntu Cloud Archive:
  Triaged
Status in Ubuntu Cloud Archive ussuri series:
  Triaged
Status in Ubuntu Cloud Archive victoria series:
  Triaged
Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  Fix Released
Status in neutron source package in Focal:
  Triaged
Status in neutron source package in Groovy:
  Fix Committed
Status in neutron source package in Hirsute:
  Fix Released

Bug description:
  [Impact]
  When neutron schedules snat namespaces it sometimes deletes the rfp interface from qrouter namespaces which breaks external network (fip) connectivity. The fix prevents this from happening.

  [Test Case]
   * deploy Openstack (Ussuri or above) with dvr_snat enabled in compute hosts.
   * ensure min. 2 compute hosts
   * create one ext network and one private network
   * add private subnet to router and ext as gateway
   * check which compute has the snat ns (ip netns| grep snat)
   * create a vm on each compute host
   * check that qrouter ns on both computes has rfp interface
   * ip netns| grep qrouter; ip netns exec <ns> ip a s| grep rfp
   * disable and re-enable router
   * openstack router set --disable <router>;  openstack router set --enable <router>
   * check again
   * ip netns| grep qrouter; ip netns exec <ns> ip a s| grep rfp

  [Where problems could occur]
  This patch is in fact restoring expected behaviour and is not expected to
  introduce any new regressions.

  -------------------------------------------------------------------------

  Hello,

  In the case of dvr_snat l3 agents are deployed on hypervisors there
  can be race condition. The agent creates snat namespaces on each
  scheduled host and removes them at second step. At this second step
  agent removes the rfp interface from qrouter even when there is VM
  with floating IP on the host.

  When VM is deployed at the time of second step we can lost external
  access to VMs floating IP. The issue can be reproduced by hand:

  1. Create tenant network and router with external gateway
  2. Create VM with floating ip
  3. Ensure that VM on the hypervisor without snat-* namespace
  4. Set the router to disabled state (openstack router set --disable <router>)
  5. Set the router to enabled state (openstack router set --enabled <router>)
  6. The external access to VMs FIP have lost because L3 agent creates the qrouter namespace without rfp interface.

  Environment:

  1. Neutron with ML2 OVS plugin.
  2. L3 agents in dvr_snat mode on each hypervisor
  3. openstack-neutron-common-15.1.1-0.20200611111910.7d97420.el8ost.noarch

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