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[OpenStack Infra <1764481@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/560703
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=fab032b426e1fa89dc473c61cbf15377fe4aaff3
Submitter: Zuul
Branch:    master

commit fab032b426e1fa89dc473c61cbf15377fe4aaff3
Author: Brian Haley <bhaley@xxxxxxxxxx>
Date:   Wed Apr 11 21:22:23 2018 -0400

    Retry dhcp_release on failures
    
    Sometimes calls to dhcp_release(6) do not result in removal
    of a lease from the leases file, for example, when the release
    packet is not received by dnsmasq.  Trying more than once is
    recommended in this case.
    
    Instead of blindly trying some number of times, we monitor
    the lease file contents, and retry the dhcp_release(6) call
    when an entry still remains.  This is possible since
    dhcp_release(6) is being run from the DHCP server itself.
    We try three times and wait 0.3 seconds between tries.
    
    We also now check for any stale leases in the leases file
    that are unknown to neutron, also trying to remove them.
    
    Change-Id: Ic1864f7efbc94db1369ac7f3e2879fda86f95a11
    Closes-bug: #1764481


** Changed in: neutron
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1764481

Title:
  Sometimes dhcp_releasepackets don't reach dnsmasq

Status in neutron:
  Fix Released

Bug description:
  We have seen issues downstream where calling dhcp_release didn't cause
  the lease to be removed from the leases files used by dnsmasq.  There
  are a couple of scenarios where this could happen:

  1. The packet is simply lost, as it is UDP, even though it's being looped-back
  2. dnsmasq is reloading, so there is noone to receive it when it arrives

  For that reason we should make this more robust.  A couple of possible
  solutions are:

  1. Send the release more than once in succession.  It's probably OK to just send some small number of packets for each lease we want to release, it would easily increase the odds that one makes it through.
  2. Check the leases file to make sure dnsmasq processed the release, and re-send for those addresses that were missed.  This method is slightly more complicated, but it should also increase the odds, and should do it with fewer packets being generated.

  Each option has some overhead, but since the option is not releasing
  the lease, it's worth it.

  I have proposed option #2 already at
  https://review.openstack.org/#/c/560703/ but wanted to make sure to
  get feedback on other proposals that might also solve the issue.

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