openstack team mailing list archive

[Dan Wendlandt <dan@xxxxxxxxxx>]

tl;dr  both Quantum and nova-network will be core and fully supported
in Folsom.

Hi folks,

Thierry, Vish and I have been spending some talking about OpenStack
networking in Folsom, and in particular the availability of
nova-network now that Quantum is a core project.  We wanted to share
our current thinking with the community to avoid confusion.

With a project like OpenStack, there's a fundamental trade-off between
the rate of introducing new capabilities and the desire for stability
and backward compatibility.  We agreed that OpenStack is a point in
its growth cycle where the cost of disruptive changes is high.  As a
result, we've decided that even with Quantum being core in Folsom, we
will also continue to support nova-network as it currently exists in
Folsom.  There is, of couse, overhead to this approach, but we think
it is worth it.

With this in mind, a key question becomes: how do we "direct" users to
the networking option that is right for them.  We have the following
guidelines:

1) For users who require only very basic networking (e.g.,
nova-network Flat, FlatDHCP) there's little difference between Quantum
and nova-network is such basic use cases, so using nova's built-in
networking for these basic use cases makes sense.

2) There are many use cases (e.g., tenant API for defined topologies
and addresses) and advanced network technologies (e.g., tunneling
rather than VLANs) that Quantum enables that are simply not possible
with nova-network, so if these advanced capabilities are important to
someone deploying OpenStack, they clearly need to use Quantum.

3) There are a few things that are possible in nova-network, but not
in Quantum.  Multi-host is the most significant one, but there are
bound to be other gaps, some of which we will uncover only when people
try their particular use case with Quantum.  For these, users will
have to use nova-network, with the gaps being covered in Quantum
during Grizzly.

As a result, we plan to structure the docs so that you can do a basic
functionality Nova setup with flat networking without requiring
Quantum.  For anything beyond that, we will have an "advanced
networking" section, which describes the different advanced use of
OpenStack networking with Quantum, and also highlight reasons that a
user may still want to use nova-networking over Quantum.

Moving beyond Folsom, we expect to fully freeze the addition of new
functionality to nova-network, and likely deprecate at least some
portions of the existing nova-network functionality.  Likely this will
leave the basic flat and flat + dhcp nova networking intact, but
reduce complexity in the nova codebase by removing more advanced
networking scenarios that can also be achieved via Quantum.  This
means that even those using nova-network in Folsom should still be
evaluating Quantum if they networking needs beyond flat networking,
such that this feedback can be incorporated into the Grizzly
deliverable of Quantum.

Thanks,

Dan


-- 
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Dan Wendlandt
Nicira, Inc: www.nicira.com
twitter: danwendlandt
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