Add versioned notifications for removing a member from a server group

Registered by Takashi NATSUME on 2018-02-16

(Specless Blueprint)

Add versioned notifications for removing a member from a server group in the following cases.

* Removing a member from a server group when server group quota exceeded
* Deleting a server (a notification for server group is emitted in addition to a notification for the server.)

Related bug report: https://bugs.launchpad.net/nova/+bug/1639152

Blueprint information

Status:
Not started
Approver:
melanie witt
Priority:
Low
Drafter:
Takashi NATSUME
Direction:
Needs approval
Assignee:
Takashi NATSUME
Definition:
Pending Approval
Series goal:
None
Implementation:
Not started
Milestone target:
None

Whiteboard

This softly depends on the patch transforming the servergroup.add_member notification https://review.openstack.org/#/c/541101/ . Besides that I'm OK with this. -- gibi 2018.03.02

I'm not sure that we want to send a notification for removal of a member from a server group when server group quota is exceeded. The "remove member from server group" API is not public and the exceeded quota in this case is that of a quota recheck -- when quota is checked a second time after creating the group member to handle races. I don't think we would want to expose that to an end user. -- melwitt 2018.03.13

> I don't think we would want to expose that to an end user.

The notifications go over RPC so they wouldn't be to end users, but I also don't see much point in sending a notification for that quota failure scenario either, it's not like the instance was ever actually part of the group since it failed to build. As for the other scenario (deleting a server) that is more straight-forward but I'd like to see the proposed code for that, since it would likely involve needing to lookup the group that the server is in *before* we delete it, since there is no specific method to remove a server group member when an instance is deleted, it's all implicit. -- mriedem 20180313

Sorry, end user isn't really what I meant, but consumers of notifications (admin/operator) should ideally not be exposed to the temporary existence a server group member due to a quota recheck. (Yes, technically a call to the API could detect the temporary existence of a server group member if timed precisely right, but it seems unhelpful to emit a notification about that if we can avoid it). -- melwitt 2018.03.14

This was discussed in the nova meeting today and we would like to see the proposed code for emitting a notification when a server is deleted before approving this blueprint. -- melwitt 20180315
==> PoC: https://review.openstack.org/#/c/559076/

Gerrit topic: https://review.openstack.org/#q,topic:bp/add-server-group-remove-member-notifications,n,z

Addressed by: https://review.openstack.org/559076
    WIP: Add notifications for removing a member from a server group

(?)

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