[openstack-dev] [nova][neutron] How would nova microversion get-me-a-network in the API?

Sean Dague sean at dague.net
Mon Feb 22 20:27:14 UTC 2016

On 02/22/2016 02:50 PM, Andrew Laski wrote:
> On Mon, Feb 22, 2016, at 02:42 PM, Matt Riedemann wrote:
>> On 2/22/2016 5:56 AM, Sean Dague wrote:
>>> On 02/19/2016 12:49 PM, John Garbutt wrote:
>>> <snip>
>>>> Consider a user that uses these four clouds:
>>>> * nova-network flat DHCP
>>>> * nova-network VLAN manager
>>>> * neutron with a single provider network setup
>>>> * neutron where user needs to create their own network
>>>> For the first three, the user specifies no network, and they just get
>>>> a single NIC with some semi-sensible IP address, likely with a gateway
>>>> to the internet.
>>>> For the last one, the user ends up with a network with zero NICs. If
>>>> they then go and configure a network in neutron (and they can now use
>>>> the new easy one shot give-me-a-network CLI), they start to get VMs
>>>> just like they would have with nova-network VLAN manager.
>>>> We all agree the status quo is broken. For me, this is a bug in the
>>>> API where we need to fix the consistency. Because its a change in the
>>>> behaviour, it needs to be gated by a micro version.
>>>> Now, if we step back and created this again, I would agree that
>>>> --nic=auto is a good idea, so its explicit. However, all our users are
>>>> used to automatic being the default, all be it a very patchy default.
>>>> So I think the best evolution here is to fix the inconsistency by
>>>> making a VM with no network being the explicit option (--no-nic or
>>>> something?), and failing the build if we are unable to get a nic using
>>>> an "automatic guess" route. So now the default is more consistent, and
>>>> those that what a VM with no NIC have a way to get their special case
>>>> sorted.
>>>> I think this means I like "option 2" in the summary mail on the ops list.
>>> Thinking through this over the weekend.
>>>  From the API I think I agree with Laski now. An API shouldn't doesn't
>>> typically need default behavior, it's ok to make folks be explicit. So
>>> making nic a required parameter is fine.
>>> "nic": "auto"
>>> "nic": "none"
>>> "nic": "$name"
>>> nic is now jsonschema enforced, 400 if not provided.
>>> that being said... I think the behavior of CLI tools should default to
>>> nic auto being implied. The user experience there is different. You use
>>> cli tools for one off boots of things, so should be as easy as possible.
>>> I think this is one of the places where the UX needs of the API and the
>>> CLI are definitely different.
>>> 	-Sean
>> Is nic only required when using neutron? Or as part of the microversion 
>> are we also going to enforce this for nova-network, because if so, that 
>> seems like a step backward. But if we don't enforce that check for both 
>> neutron and nova-network, then we have differences in the API again.
> I think it makes sense to require it in both cases and keep users
> blissfully unaware of which networking service is in use.


This should make the experience between both far more consistent. It
means making n-net API applications do a bit more work then now, but
it's explicit.

It also means the CLI experience should continue to be the same, because
--nic=auto is implied.


Sean Dague

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