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[Bug 2089225] [NEW] The description of the heal_instance_info_cache_interval option is misleading

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Balazs Gibizer <2089225@xxxxxxxxxxxxxxxxxx>
Date: Thu, 21 Nov 2024 08:24:43 -0000
Reply-to: Bug 2089225 <2089225@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx

Public bug reported:

The current doc text is:

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.

There is a list of improvement we could make in the text / implementation of the periodic to make it clearer:
* Currently setting it to 0 make the periodic run at the default interval and exit early[2]. While setting it to -1 disables the whole periodic. We should remove this complication and simply make sure that if it is set to <=0 then the periodic is not started.

* Disabling the periodic is not dangerous any more with the most used
neutron backends like the in tree ovs, ovn, sriov backends as they are
properly updating nova's view with network-changed external events[1].
So we should clarify this in the text.

[1]https://github.com/openstack/nova/blob/e8a544f0e1134a4b260720cc634ad1997f936d6d/nova/compute/manager.py#L11135-L11140
[2]https://github.com/openstack/nova/blame/e8a544f0e1134a4b260720cc634ad1997f936d6d/nova/compute/manager.py#L9909-L9924

** Affects: nova
Importance: Undecided
Status: New

** Tags: doc neutron

** Tags added: doc neutron

** Description changed:

The current doc text is:

Interval between instance network information cache updates.

Possible values:

Any positive integer in seconds.

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

There is a list of improvement we could make in the text / implementation of the periodic to make it clearer:
- * Currently setting it to 0 make the periodic run at the default interval and exit early. While setting it to -1 disables the whole periodic. We should remove this complication and simply make sure that if it is set to <=0 then the periodic is not started.
+ * Currently setting it to 0 make the periodic run at the default interval and exit early[2]. While setting it to -1 disables the whole periodic. We should remove this complication and simply make sure that if it is set to <=0 then the periodic is not started.

-
[1]https://github.com/openstack/nova/blob/e8a544f0e1134a4b260720cc634ad1997f936d6d/nova/compute/manager.py#L11135-L11140
+ [2]https://github.com/openstack/nova/blame/e8a544f0e1134a4b260720cc634ad1997f936d6d/nova/compute/manager.py#L9909-L9924

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https://bugs.launchpad.net/bugs/2089225

Title:
The description of the heal_instance_info_cache_interval option is
misleading

Status in OpenStack Compute (nova):
New

Bug description:
The current doc text is:

Interval between instance network information cache updates.

Possible values:

Any positive integer in seconds.

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

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