Open Stack

Hi,

I'm currently working on solving Nova-Neutron issues during Live
Migration. This mail is intended to raise awareness cross project and
get things kicked off.

The issues
==========

#1 When portbinding fails, instance is migrated but stuck in error state
#2 Macvtap agent live Migration when source and target use different
physical_interface_mapping [3]. Either the migration fails (good case)
or it would place the instance on a wrong network (worst case)
#3 (more a feature):  Migration cross l2 agent not possible (e.g.
migrate from lb host to ovs host, or from ovs-hybrid to new ovsfirewall
host)


The proposal
============
All those problems could be solved with the same approach . The proposal
is, to bind a port to the source AND to the target port during
migration.

* Neutron would need to allow multiple bindings for a compute port and
externalize that via API. 
  - Neutron Spec [1]
  - Bug [4]  is a prereq to the spec.

* Nova would need to use those new APIs to check in pre_live_migration,
if the binding for target host is valid and to modify the instance
definition (e.g. domain.xml) during migration.
  - Nova Spec [2]

This would solve the issues in the following way:
#1 would abort the migration before it started, so instance is still
usable
#2 Migration is possible with all configurations 
#3 would allow such a migration


Coordination
============
Some coordination between Nova & Neutron is required. Along todays Nova
Live Migration Meeting [5] this will happen on the Nova midcycle. I put
an item on the agenda [6].


Would be great that anybody that is interested in this bugfix/feature
could comment on the specs [1] or [2] to get as much feedback as
possible before the nova midcycle in July!

Thank you!



[1] Neutron spec: https://review.openstack.org/#/c/309416
[2] Nova spec: https://review.openstack.org/301090
[3] macvtap bug: https://bugs.launchpad.net/neutron/+bug/1550400
[4] https://bugs.launchpad.net/neutron/+bug/1367391
[5]
http://eavesdrop.openstack.org/meetings/nova_live_migration/2016/nova_live_migration.2016-06-28-14.00.log.html

[6] https://etherpad.openstack.org/p/nova-newton-midcycle





andreas_s