Hi,

I had conversations last week with a number of you about this topic, and
just wanted to strike while the iron was hot to get it on the Be
planning cycle (if any work needs doing).

When someone is deciding to use ODL for OpenStack Neutron, my
expectation would be that they're not starting from scratch - in all
probability, either they are currently using nova-network or they're
using the defail OVS ML2 plug-in.

Migrating from nova-network to Neutron is already a hairy topic, but
migrating an existing cloud from OVS to ODL easily would make it easier
to adopt ODL. My understanding before last week was that you didn't have
a choice - to migrate to ODL from OVSDB required deleting and
reinitialising the ovsdb database on all of the Nova compute nodes, as
documented here:
https://wiki.opendaylight.org/view/OpenStack_and_OpenDaylight

But in conversation last week, the following procedure was suggested. My
question is, can we document and test this, and verify that it works?

Migration procesure:

0. Install and start ODL
1. Stop neutron-service (doesn't affect dataplane for existing instances)
2. On each OVS instance: stop and disable neutron-openvswitch-agent
3. Update Neutron config to use ODL mechanism
4. On each OVS instance: set-manager to ODL

It'll be important for Neutron to be connected to ODL before setting ODL
as the manager for the vswitch, as once you do a set-manager, ODL will
write flows to the switches. The contention is, since the compute
instances are still connected to OVS, the set-manager will also kick off
ovsdb events which will lead to everything converging on a consistent
state - ODL will wipe any old flows from the switches, and will rewire
instances to the appropriate network IDs, and set all the flows, vlan
tags, etc as they should be.

Will this work? I'm going to try it out when I get home (in a few days),
but I wanted to get something written down & argued about ASAP.

Thanks,
Dave.

--
Dave Neary - NFV/SDN Community Strategy
Open Source and Standards, Red Hat - http://community.redhat.com
Ph: +1-978-399-2182 / Cell: +1-978-799-3338