[Standards] distributed MUC rooms

Peter Saint-Andre stpeter at jabber.org
Mon Jun 4 11:40:48 CDT 2007


Mridul Muralidharan wrote:
> Peter Saint-Andre wrote:
>> Last October I talked with some folks in the XMPP community about the 
>> idea of distributing MUC rooms across domains. Late this afternoon and 
>> this evening I finally got around to writing up an approach to this 
>> problem. The document I've started working on is quite tentative, but 
>> I figured I'd send it out for feedback anyway (release early, release 
>> often!).
>>
>> http://www.xmpp.org/extensions/inbox/distributedmuc.html
>>
>> I'll try to work on it more this weekend, since I'd like to present 
>> some of the ideas at a conference I'm attending next week.
>>
>> Peter
>>
> 
> A few thoughts in general.
> 
> 1) What is the scope of the distribution - is it going to be an muc 
> service spread across domains ? Or is it going to be a single logical 
> muc service (hosted on multiple machines/nodes) ? (With reference to 1.3.3)

Multiple domains.

>  From examples 5 onwards, it looks like the former case ... might get a 
> bit tricky. Why would a user join muc.example.net for a conference on 
> chat.example.com ?

The conference is (say) "topside" and the conference is the same logical 
conference whether you join on muc.example.net or chat.example.com. Or 
at least that is the idea.

> Wont this not be a potential routing issue ?
> I assumed we will be using something like dix[1] for this - where bare 
> jid is the same, just that it is distributed and fault tolerant. (or 
> integrated into the cluster/pool'ed server).

IMHO clustering or pooling is trying to solve a different problem.

> This could also become potentially confusing for clients - where user of 
> a conference is receiving messages from multiple room jids.

Maybe -- I'm not sure what you mean. If I join topside at muc.example.net 
then as far as I can see, every occupant is in that room. The s2s aspect 
of it is hidden from the user.

> 2) After creation, do we need to maintain the distinction between 
> FIRSTHOST and PEERHOST ? Merging of config can be based on 'timestamp' 
> for example (use ntp on all nodes to keep them in sync) ? This way, 
> FIRSTHOST could be down, or not participating in the conference which 
> was created on it ... and still things would continue working.
> With reference to 1.3.4

Possibly, yes. I think it's a requirement that any and all peerhosts can 
continue operating even if the firsthost is not available temporarily or 
goes down permanently. But it's not yet clear to me how the all the 
peerhosts figure out what the canonical room configuration is. In a way, 
the firsthost is like the room owner and the peerhosts are like room 
admins (across domains). Right now we don't have a good way of 
proceeding if in a non-distributed room the room owner disappears from 
the scene (but for non-distributed rooms we at least have a service-wide 
MUC admin). So it seems we almost want a way to have net-wide admins who 
can administer the network of peerhosts in some way. I have not given a 
lot of thought to these issues yet.

> 3) After example 4, can we add the peerhost as a hidden config param to 
> the room config (firsthost gets auto-added if room is distributed) ?
> This way, recovery would be easier in case of restart/etc - and peerhost 
> will know 'who all' to talk to for a room.
> Though in light of (1), I am not very sure of this - if it is a single 
> logical entity, it will talk to 'all' instances it discovers ... so wont 
> be necessary.

Yes, I think that peering is something that is set up at the service 
level. So muc.example.net knows that it peers with chat.example.com and 
conference.example.org. If a room is distributed, then the service knows 
which peers it must sync with. So I don't think we need a room-level 
param for this.

> 4) Section 3.4 - is it that the peer room which received the message 
> supposed to be multicast to other peer rooms - which will inturn 
> multicasts to their hosted participants ? 

Yes.

> Or is it that the recipients 
> room multicast directly to participants of the remote rooms ?

No.

> Would prefer the former - if latter, use xep 33 ?
> I was not sure which approach this xep is taking (I could have missed it).

Perhaps I didn't make it clear yet.

> We have been supporting distributed conferences for a while now, and 
> there are some interesting routing challenges - even though in our case 
> it is directly integrated into the server.
> It would be great to see a spec which allow remote components to also 
> become distributed and provide highly available conference service !

Do you mean in general (i.e., a generalized spec for service 
distribution)? Or just for MUC?

Peter

-- 
Peter Saint-Andre
XMPP Standards Foundation
http://www.xmpp.org/xsf/people/stpeter.shtml

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