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[sean mooney <1996094@xxxxxxxxxxxxxxxxxx>]

Public bug reported:


the current help text for the config option is as follows

heal_instance_info_cache_interval¶

    Type

        integer
    Default

        60

    Interval between instance network information cache updates.

    Number of seconds after which each compute node runs the task of
querying Neutron for all of its instances networking information, then
updates the Nova db with that information. Nova will never update it’s
cache if this option is set to 0. If we don’t update the cache, the
metadata service and nova-api endpoints will be proxying incorrect
network data about the instance. So, it is not recommended to set this
option to 0.

    Possible values:

        Any positive integer in seconds.

        Any value <=0 will disable the sync. This is not recommended.


this is not correct.

when the value is set to 0 it will disable the periodic task so nova
will not try to heal the cache but the cache will still get updated if
neutron notifies us of a change.

every time neutron emits a network-changed event for an interface nova
updates that interface in the info cache.

the reason that setting the value to 0 is not recommended has nothing to
do with what the current help text states. it's not recommended because
it is not tested today.

in large deployments with many compute agents it may be better for
scaling to disable this periodic.

for environments that use ironic or a clustered hypervisor like vmware
the default will not introduce a performance issue but it will take a
very long time to heal all the nodes if there is an issue. that this
would fix.

as a result it is likely better to diabel this longterm.

for now we should just fix the help text and add testing fo disabling
this in a ci job.

** Affects: nova
     Importance: Low
         Status: Triaged


** Tags: db network

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https://bugs.launchpad.net/bugs/1996094

Title:
  heal_instance_info_cache_interval help text is inaccurate

Status in OpenStack Compute (nova):
  Triaged

Bug description:
  
  the current help text for the config option is as follows

  heal_instance_info_cache_interval¶

      Type

          integer
      Default

          60

      Interval between instance network information cache updates.

      Number of seconds after which each compute node runs the task of
  querying Neutron for all of its instances networking information, then
  updates the Nova db with that information. Nova will never update it’s
  cache if this option is set to 0. If we don’t update the cache, the
  metadata service and nova-api endpoints will be proxying incorrect
  network data about the instance. So, it is not recommended to set this
  option to 0.

      Possible values:

          Any positive integer in seconds.

          Any value <=0 will disable the sync. This is not recommended.


  this is not correct.

  when the value is set to 0 it will disable the periodic task so nova
  will not try to heal the cache but the cache will still get updated if
  neutron notifies us of a change.

  every time neutron emits a network-changed event for an interface nova
  updates that interface in the info cache.

  the reason that setting the value to 0 is not recommended has nothing
  to do with what the current help text states. it's not recommended
  because it is not tested today.

  in large deployments with many compute agents it may be better for
  scaling to disable this periodic.

  for environments that use ironic or a clustered hypervisor like vmware
  the default will not introduce a performance issue but it will take a
  very long time to heal all the nodes if there is an issue. that this
  would fix.

  as a result it is likely better to diabel this longterm.

  for now we should just fix the help text and add testing fo disabling
  this in a ci job.

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