[openstack-dev] [Nova][Neutron] Status of the nova-network to Neutron migration work

Sean Dague sean at dague.net
Fri Mar 27 17:17:34 UTC 2015

On 03/27/2015 11:48 AM, Assaf Muller wrote:
> ----- Original Message -----
>> On 03/27/2015 05:22 AM, Thierry Carrez wrote:
>> <snip>
>>> Part of it is corner (or simplified) use cases not being optimally
>>> served by Neutron, and I think Neutron could more aggressively address
>>> those. But the other part is ignorance and convenience: that Neutron
>>> thing is a scary beast, last time I looked into it I couldn't make sense
>>> of it, and nova-network just works for me.
>>> That is why during the Ops Summit we discussed coming up with a
>>> migration guide that would explain the various ways you can use Neutron
>>> to cover nova-network use cases, demystify a few dark areas, and outline
>>> the step-by-step manual process you can go through to migrate from one
>>> to the other.
>>> We found a dev/ops volunteer for writing that migration guide but he was
>>> unfortunately not allowed to spend time on this. I heard we have new
>>> volunteers, but I'll let them announce what their plans are, rather than
>>> put words in their mouth.
>>> This migration guide can happen even if we follow the nova-net spinout
>>> plan (for the few who want to migrate to Neutron), so this is a
>>> complementary solution rather than an alternative. Personally I doubt
>>> there would suddenly be enough people interested in nova-net development
>>> to successfully spin it out and maintain it. I also agree with Russell
>>> that long-term fragmentation at this layer of the stack is generally not
>>> desirable.
>> I think if you boil everything down, you end up with 3 really important
>> differences.
>> 1) neutron is a fleet of services (it's very micro service) and every
>> service requires multiple and different config files. Just configuring
>> the fleet is a beast if it not devstack (and even if it is)
>> 2) neutron assumes a primary interesting thing to you is tenant secured
>> self service networks. This is actually explicitly not interesting to a
>> lot of deploys for policy, security, political reasons/restrictions.
>> 3) neutron open source backend defaults to OVS (largely because #2). OVS
>> is it's own complicated engine that you need to learn to debug. While
>> Linux bridge has challenges, it's also something that anyone who's
>> worked with Linux & Virtualization for the last 10 years has some
>> experience with.
>> (also, the devstack setup code for neutron is a rats nest, as it was
>> mostly not paid attention to. This means it's been 0 help in explaining
>> anything to people trying to do neutron. For better or worse devstack is
>> our executable manual for a lot of these things)
>> so.... that being said, I think we need to talk about "minimum viable
>> neutron" as a model and figure out how far away that is from n-net. This
>> week at the QA Sprint, Dean, Sean Collins, and I have spent some time
>> hashing it out, hopefully with something to show the end of the week.
>> This will be the new devstack code for neutron (the old lib/neutron is
>> moved to lib/neutron-legacy).
>> Default setup will be provider networks (which means no tenant
>> isolation). For that you should only need neutron-api, -dhcp, and -l2.
>> So #1 is made a bunch better. #2 not a thing at all. And for #3 we'd
>> like to revert back to linux bridge for the base case (though first code
>> will probably be OVS because that's the happy path today).
> Looking at the latest user survey, OVS looks to be 3 times as popular as
> Linux bridge for production deployments. Having LB as the default seems
> like an odd choice. You also wouldn't want to change the default before
> LB is tested at the gate.

Sure, actually testing defaults is presumed here. I didn't think it
needed to be called out separately.


Sean Dague

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