Open Stack

Neutron land,

Problem:
Neutron currently only allows a single network segment per host. This
becomes a problem when networking teams want to limit the number of IPs it
supports on a segment. This means that at times the number of IPs available to
the host is the limiting factor for the number of instances we can deploy on a
host. Ref: https://bugs.launchpad.net/neutron/+bug/1764738

Ongoing Work:
We are excited in our work add "multi-segment support for routed networks".
We currently have a proof of concept here https://review.openstack.org/#/c/623115
that for routed networks effectively:
* Removes validation preventing multiple segments.
* Injects segment_id into fixed IP records.
* Uses the segment_id when creating a bridge (rather than network_id).
In effect, it gives each segment its own bridge.

It works pretty well for new networks and deployments. For existing
routed networks, however, it breaks networking. Please use *caution* if you
decide to try it.

TODOs:
Things TODO before this before it is fully baked:
* Need to add code to handle ensuring bridges are also updated/deleted using
  the segment_id (rather than network_id).
* Need to add something (a feature flag?) that prevents this from breaking
  routed networks when a cloud admin updates to master and is configured for
  routed networks.
* Need to create checker and upgrade migration code that will convert existing
  bridges from network_id based to segment_id based (ideally live or with
  little network traffic downtime). Once converted, the feature flag could
  enable the feature and start using the new code.

Need:
1. How does one go about adding a migration tool? Maybe some examples?
2. Will nova need to be notified/upgraded to have bridge related files updated?
3. Is there a way to migrate without (or minimal) downtime?
4. How to repeatably test this migration code? Grenade?

Looking for any ideas that can keep this moving :)

Thanks a ton,

David Bingham (wwriverrat on irc)
Kris Lindgren (klindgren on irc)
Cloud Engineers at GoDaddy