On 27/11/12 10:53, Alon Bar-Lev wrote:
> 
> 
> ----- Original Message -----
>> From: "Livnat Peer" <lp...@redhat.com>
>> To: "Adam Litke" <a...@us.ibm.com>
>> Cc: "Alon Bar-Lev" <abar...@redhat.com>, "VDSM Project Development" 
>> <vdsm-devel@lists.fedorahosted.org>
>> Sent: Tuesday, November 27, 2012 10:42:00 AM
>> Subject: Re: [vdsm] Future of Vdsm network configuration - Thread mid-summary
>>
>> On 26/11/12 16:59, Adam Litke wrote:
>>> On Mon, Nov 26, 2012 at 02:57:19PM +0200, Livnat Peer wrote:
>>>> On 26/11/12 03:15, Shu Ming wrote:
>>>>> Livnat,
>>>>>
>>>>> Thanks for your summary.  I got comments below.
>>>>>
>>>>> 2012-11-25 18:53, Livnat Peer:
>>>>>> Hi All,
>>>>>> We have been discussing $subject for a while and I'd like to
>>>>>> summarized
>>>>>> what we agreed and disagreed on thus far.
>>>>>>
>>>>>> The way I see it there are two related discussions:
>>>>>>
>>>>>>
>>>>>> 1. Getting VDSM networking stack to be distribution agnostic.
>>>>>> - We are all in agreement that VDSM API should be generic enough
>>>>>> to
>>>>>> incorporate multiple implementation. (discussed on this thread:
>>>>>> Alon's
>>>>>> suggestion, Mark's patch for adding support for netcf etc.)
>>>>>>
>>>>>> - We would like to maintain at least one implementation as the
>>>>>> working/up-to-date implementation for our users, this
>>>>>> implementation
>>>>>> should be distribution agnostic (as we all acknowledge this is
>>>>>> an
>>>>>> important goal for VDSM).
>>>>>> I also think that with the agreement of this community we can
>>>>>> choose to
>>>>>> change our focus, from time to time, from one implementation to
>>>>>> another
>>>>>> as we see fit (today it can be OVS+netcf and in a few months
>>>>>> we'll use
>>>>>> the quantum based implementation if we agree it is better)
>>>>>>
>>>>>> 2. The second discussion is about persisting the network
>>>>>> configuration
>>>>>> on the host vs. dynamically retrieving it from a centralized
>>>>>> location
>>>>>> like the engine. Danken raised a concern that even if going with
>>>>>> the
>>>>>> dynamic approach the host should persist the management network
>>>>>> configuration.
>>>>>
>>>>> About dynamical retrieving from a centralized location,  when
>>>>> will the
>>>>> retrieving start? Just in the very early stage of host booting
>>>>> before
>>>>> network functions?  Or after the host startup and in the normal
>>>>> running
>>>>> state of the host?  Before retrieving the configuration,  how
>>>>> does the
>>>>> host network connecting to the engine? I think we need a basic
>>>>> well
>>>>> known network between hosts and the engine first.  Then after the
>>>>> retrieving, hosts should reconfigure the network for later
>>>>> management.
>>>>> However, the timing to retrieve and reconfigure are challenging.
>>>>>
>>>>
>>>> We did not discuss the dynamic approach in details on the list so
>>>> far
>>>> and I think this is a good opportunity to start this discussion...
>>>>
>>>> From what was discussed previously I can say that the need for a
>>>> well
>>>> known network was raised by danken, it was referred to as the
>>>> management
>>>> network, this network would be used for pulling the full host
>>>> network
>>>> configuration from the centralized location, at this point the
>>>> engine.
>>>>
>>>> About the timing for retrieving the configuration, there are
>>>> several
>>>> approaches. One of them was described by Alon, and I think he'll
>>>> join
>>>> this discussion and maybe put it in his own words, but the idea
>>>> was to
>>>> 'keep' the network synchronized at all times. When the host have
>>>> communication channel to the engine and the engine detects there
>>>> is a
>>>> mismatch in the host configuration, the engine initiates 'apply
>>>> network
>>>> configuration' action on the host.
>>>>
>>>> Using this approach we'll have a single path of code to maintain
>>>> and
>>>> that would reduce code complexity and bugs - That's quoting Alon
>>>> Bar Lev
>>>> (Alon I hope I did not twisted your words/idea).
>>>>
>>>> On the other hand the above approach makes local tweaks on the
>>>> host
>>>> (done manually by the administrator) much harder.
>>>
>>> I worry a lot about the above if we take the dynamic approach.  It
>>> seems we'd
>>> need to introduce before/after 'apply network configuration' hooks
>>> where the
>>> admin could add custom config commands that aren't yet modeled by
>>> engine.
>>>
>>
>> yes, and I'm not sure the administrators would like the fact that we
>> are
>> 'forcing' them to write everything in a script and getting familiar
>> with
>> VDSM hooking mechanism (which in some cases require the use of custom
>> properties on the engine level) instead of running a simple command
>> line.
> 
> In which case will we force? Please be more specific.
> If we can pass most of the iproute2, brctl, bond parameters via key/value 
> pairs via the API, what in your view that is common or even seldom should be 
> used?
> This hook mechanism is only as fallback, provided to calm people down.
> 

I understand, I'm saying it can irritate the administrators that needs
to use it, it does not help that we are calmed down ;)

Just to make it clear I'm not against the stateless approach, I'm trying
to understand it better and make sure we are all aware of the drawbacks
this approach has. Complicating local tweaks to the admin is one of them.

I'll reply on your original mail with the questions I have on your proposal.

>>
>>>> Any other approaches ?
>>>
>>> Static configuration has the advantage of allowing a host to bring
>>> itself back
>>> online independent of the engine.  This is also useful for anyone
>>> who may want
>>> to deploy a vdsm node in standalone mode.
>>>
>>> I think it would be possible to easily support a quasi-static
>>> configuration mode
>>> simply by extending the design of the dynamic approach slightly.
>>>  In dynamic
>>> mode, the network configuration is passed down as a well-defined
>>> data structure.
>>> When a particular configuration has been committed, vdsm could
>>> write a copy of
>>> that configuration data structure to
>>> /var/run/vdsm/network-config.json.  During
>>> a subsequent boot, if the engine cannot be contacted after
>>> activating the
>>> management network, the cached configuration can be applied using
>>> the same code
>>> as for dynamic mode.  We'd have to flesh out the circumstances
>>> under which this
>>> would happen.
>>
>> I like this approach a lot but we need to consider that network
>> configuration is an accumulated state, for example -
>>
>> 1. The engine sends a setup-network command with the full host
>> network
>> configuration
>> 2. The user configures new network on the host, the engine sends a
>> new
>> setup-network request to VDSM which includes only the delta requested
>> by
>> the user (adding the required network)
>> 3. VDSM adds the new network
> 
> THIS IS COMPLEX!!!!!!!
> Almost AI.
> As you need to complete the network setting with what you know.
> 

I think we should clear this first -
We have a running hypervisor with running VMs on it, we would like to
configure an additional network on the host.
You don't want to apply the network-configuration from scratch and mess
with the running VMs networks or the storage network or anything else
that is running and was not change by the administrator ==> you need to
calculate the delta of the changes to perform as less intrusive
operation as possible.


>> and this can go on and on, for dealing with this issue:
>>
>> We can either hold network-config.json per setup-network command and
>> then for recovering the network configuration state we need to
>> execute
>> chain of set-up networks commands.
>>
>> Or we can move the logic of calculating the delta from engine to VDSM
>> and on each setup network have the engine pass the full
>> configuration.
>> The problem with that approach is that the analysis logic of the
>> delta
>> has to be done on the engine anyway to give a quick feedback to the
>> user
>> on the validity of his action.
>> Maintaining this logic/code twice is not something we want (it's bad
>> enough to do it once....)
> 
> I don't understand how the two algorithm are the same...
> UI is much more/less verbose at different aspects, while taking the full 
> configuration and convert to actual setting is a completely different 
> sequence.
> What the feedback of the user? as far as I understand the user is only 
> interested in the end-result... building his own network and expect it to be 
> applied.
>  
>> A third option is to extend the current API of setup network to
>> include
>> the full configuration in addition to the delta that is sent today.
>> The
>> full configuration would be used for creating network-config.json and
>> for that alone, VDSM would change network configuration according to
>> the
>> delta sent as it does today.
> 
> Always pass full configuration, why deal with two cases?
> 
>> The problem with that approach is that I'm sure someone on the list
>> would say it is a contamination to the API, and we should 'never'
>> pass
>> 'duplicate' information. Personally I find this option the easiest
>> one
>> to deal with the above issue.
>>
> 
> Livnat, I don't see any argument of persistence vs non persistence as the 
> above is common to any approach taken.
> 
> Only this "manual configuration" argument keeps poping, which as I wrote is 
> irrelevant in large scale and we do want to go into large scale.
> 
> Alon
> 
>>
>> Livnat
>>
>>>
>>>>
>>>> I'd like to add a more general question to the discussion what are
>>>> the
>>>> advantages of taking the dynamic approach?
>>>> So far I collected two reasons:
>>>>
>>>> -It is a 'cleaner' design, removes complexity on VDSM code, easier
>>>> to
>>>> maintain going forward, and less bug prone (I agree with that one,
>>>> as
>>>> long as we keep the retrieving configuration mechanism/algorithm
>>>> simple).
>>>>
>>>> -It adheres to the idea of having a stateless hypervisor - some
>>>> more
>>>> input on this point would be appreciated
>>>>
>>>> Any other advantages?
>>>>
>>>> discussing the benefits of having the persisted
>>>
>>> As I mentioned above, the main benefit I see of having some sort of
>>> persistent
>>> configuration is:
>>>
>>> - To allow the host to operate independently of the engine in
>>> either a failure
>>>   scenario or in a standalone configuration.
>>>
>>
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>>

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