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From: Jan Lehnardt <jan@apache.org>
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Subject: Re: Peer to peer replication
Date: Sat, 7 Mar 2009 11:41:55 +0100
References: <56a83cd00903070158yb0eac89xaa433c6f120ee667@mail.gmail.com>
 <6B20EBBA-8AB4-4D1A-93A2-90A1FAFBCEEC@apache.org>
 <56a83cd00903070221h407c4478oa32a053741d149fb@mail.gmail.com>


On 7 Mar 2009, at 11:21, David Van Couvering wrote:
>> - What protocol is used for replication across nodes?  I'm assuming  
>> it's
>>> HTTP but just checking.  In a peer-to-peer system, this sounds  
>>> like it
>>> means
>>> that each participant has to open up their HTTP port for  
>>> replication to
>>> work.  Is that correct?
>>
>> Yes.
>
> Hm.  I am concerned that your Average Joe does not like the idea of  
> opening
> up their HTTP port, and probably doesn't know how to.  Folks used to  
> hacking
> with BitTorrent maybe, but that's not the target user I was really
> considering.
>
> I was thinking of maybe piggybacking replication messages on a  
> protocol that
> already supports push over the Internet and works for most users -  
> like
> XMPP.
>
> But I'm not an expert in network protocols/security, and before I  
> jump into
> that, I am wondering if there are simpler solutions so that it's  
> Very Easy
> for Mr. Average Joe or Jill to install a CouchDB app where peer-to- 
> peer
> replication Just Works.

This an open issue, you're right. I don't think the protocol matters  
as much.
The "common trick" is to setup an intermediate server machine that all  
peers
can push to and pull from (replication is both, push and pull). I  
don't think
XMPP magically opens ports for users :)

That said, there are a couple ways around this problem and the best is  
to
combine them all which I believe is what Skype does which in my  
experience
works quite well in this regard.

[And then I start writing about the technique and when I was looking for
references, I found these, so I just give you the links and spare you my
ramblings :)]

http://www.h-online.com/security/How-Skype-Co-get-round-firewalls--/features/82481
http://sebsauvage.net/punching/

Searching for "firewall punching" gives you some more resources.

Cheers
Jan
--