ovirt-quantum integration

Wed Nov 28 11:34:23 UTC 2012

On 27/11/12 16:34, Gary Kotton wrote:
> On 11/27/2012 04:06 PM, Mike Kolesnik wrote:
>> Thanks for the reply,
>> Please see comments inline
>>

Hi Garry,
Thanks for your input, see my comments inline.

Livnat

>> ----- Original Message -----
>>> On 11/27/2012 03:01 PM, Livnat Peer wrote:
>>>> Hi All,
>>>> Mike Kolesnik and me have been working on a proposal for
>>>> integrating
>>>> quantum into oVirt in the past few weeks.
>>>> We decided to focus our efforts on integrating with quantum
>>>> services, we
>>>> started with IP address management service.
>>>>
>>>> here is a link to our proposal:
>>>> http://wiki.ovirt.org/wiki/Quantum_IPAM_Integration
>>>>
>>>> As usual comments are welcome,
>>> Please see my comments below:
>>>
>>> i. The quantum diagram is incorrect. It is the same message queue
>>> that
>>> passes the notifications. This is done by a message broker. In RH we
>>> are
>>> supporting qpid and in the community upstream rabbitmq is used.
>> I will fix the diagram accordingly
> 
> Thanks
>>
>>> ii. The DHCP agent is plugable. That is there may be more than one
>>> implementation. At the moment only dnsmasq is support. There was a
>>> company working on ISC upstream but they have stopped due to problem
>>> they encountered.
>>> iii. Layer 3 driver. This is incorrect. The layer 2 agent does the
>>> network connectivity. The layer 3 agent provides floating IP support.
>>> This is something that you may want to consider to. It is related to
>>> IPAM

>From what we gathered from code the DHCP Agent is communicating with (an
implementation of the) LinuxInterfaceDriver, which is not the same as
the layer 2 agent used in the plugin.

For example, looking in Linux bridge, the plugin has
Linux_bridge_quantum agent that is part of the Linux bridge plugin, and
it has (what we called Layer 3 driver) a BridgeInterfaceDriver that is
used within the DHCP Agent.

Maybe we used a misleading terminology but 'layer 2 agent' is also
misleading, IMO, as it is already used in the plugin context and this is
not the same component.

We'll update the doc to call it 'layer 2 driver'.

>>> iv. I am not really sure I understand you picture with server B and
>>> get/create network. This is not really what happens. If you want I
>>> can
>>> explain.
>> We saw that the DHCP Agent is trying to create the network interface
>> if it doesn't exist (in DeviceManager.setup which is called as part of
>> "enable_dhcp_helper").
>>
>> If you want to elaborate on this, please do.
> 
> The DHCP agent will create a device that is used by the dnsmasq process.
> The creation is done according to a driver that is used for the
> underlying l2 implementation. It does not have anything to do the the
> layer 3 agent. 

Again the same terminology misunderstanding.

> It creates a network device and assigns it an IP address.
> The layer 2 agent (if there is one) will attach this device to the
> underlying virtual network.

It seems to be our understanding and what we have described in the wiki
page, do you see something wrong there?

> Prior to doing anything the DHCP agent will create a quantum port on the
> subnet. This is how it receives its own IP address.
> 
>>
>>> v. What do you mean by the "port is then part of the Quantum DB". Not
>>> all plugins maintain a database.
>> True but if it's not saved somewhere then how does the Agent know
>> which IP to assign to which MAC?
> 
> The DHCP agent is notified by the Quantum service of a new port
> allocation. It is passed the port details - the mac address and the IP
> address. The plugin may not use a database that one can access. All of
> the interface to the data is done via the Quantum API. For example the NVP.
> 
>>
>>> vi. I think that you are missing useful information about the subnets
>>> and gateways. This is also a critical part of the IPAM. When a VM
>>> sends
>>> a DHCP request it not only gets and IP but it can also receive host
>>> route information. This is very important.
>> can you please elaborate on this?
> 
> When you reboot your computer at work you get access to the internet.
> This is done via DHCP. You get an IP address and all of the relevant
> routes configured. The port data has the 'host_routes' which is also
> used by the dnsmasq. There can be more than one route which is
> configured. The subnet contains the gateway IP.
> 

We assumed that when creating the subnet in Quantum it would update the
DHCP Agent with all the information oVirt will provide as part of the
subnet details (dns_nameservers, host_routes, gateway_ip  etc).
Isn't this the case?

>>
>>> vii. The DHCP agent dynamics are incorrect (l3 agent, write port
>>> definitions etc.). One of the pain points is that the process is for
>>> each quantum network. This is a scale issue and is being discussed
>>> upstream.
>> This is what we saw that happens in the code, if we are wrong please
>> explain what is the right behaviour of the DHCP Agent.
> 
> For each network that has one or more subnets with DHCP support a
> dnsmasq process is created. Please see http://fpaste.org/IHbA/. Here I
> have two networks.

That's exactly what we have described in the wiki. dnsmasq per network.
In the integration with oVirt we planned that the ovirt layer2 driver
will not return interface_name where there is no need for the dnsmasq
locally on the host.
This requires a patch to Quantum that in case the driver returns empty
device name the dnsmasq won't be started.
We'll send a patch for that soon.
I added that to the wiki as well.

> 
>>
>>> viii. Quantum does not require homogeneous  hardware. This is
>>> incorrect.
>>> There is something called a provider network that addresses this.
>> Can you please elaborate?
> 
> When you create a network you can indicate which NIC connects to the
> outside world. If you look at
> http://wiki.openstack.org/ConfigureOpenvswitch then you will see the
> bridge mappings. This information is passed via the API.

Our understanding is that Quantum IPAM design assumes the DHCP Agent has
local access to *ALL* the networks created in quantum.
Per Network it spawns a local dnsmasq and connect it to the network
(which should be accessible from within the host on which the DHCP Agent
is running on).

This assumption is problematic in the oVirt context and this is the
issue we were trying to overcome in the proposed integration.

>>
>>> ix. I do not udnerstand the race when the VM starts. There is none.
>>> When
>>> a VM starts it will send a DHCP request. If it does not receive one
>>> it
>>> will send another after a timeout. Can you please explain the race?
>> This is exactly it, the VM might start requesting DHCP lease before it
>> was updated in the DHCP server, for us it's a race.
> 
> This works. This is how DHCP is engineered. Can you please explain the
> problem? If you send a DHCP request and do not get a reply then you send
> one again. The timeout between requests is incremental.
> 
> I am not sure that we are on the same page when it comes to a race
> condition. I'd like you to clarify.
>>
>>> You do not need to consume Quantum to provide IPAM. You can just run
>>> the
>>> dnsmasq and make sure that its interface is connected to the virtual
>>> network. This will provide you with the functionality that you are
>>> looking for. If you want I go can over the dirty details. It will be
>>> far
>>> less time than consuming Quantum and you can achieve the same goal.
>>> You
>>> just need to be aware when the dnsmasq is running to sent the
>>> updates.
>>>
>>> IPAM is one of the many features that Quantum has to offer. It will
>>> certain
>>> help oVirt.
>>>
>>> Thanks
>>> Gary
> 
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