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From: Damien Katz <damien@apache.org>
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Subject: Re: Peer to peer replication
Date: Sat, 7 Mar 2009 08:31:38 -0500
References: <56a83cd00903070158yb0eac89xaa433c6f120ee667@mail.gmail.com>
 <6B20EBBA-8AB4-4D1A-93A2-90A1FAFBCEEC@apache.org>
 <56a83cd00903070221h407c4478oa32a053741d149fb@mail.gmail.com>
 <682AC08E-95FF-4847-9373-CF9268AE0323@apache.org>


On Mar 7, 2009, at 5:41 AM, Jan Lehnardt wrote:

>
> 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 :)

1+

Peers who cannot connect to one another can replicate to a publicly  
accessible server to achieve the same thing. Also, with a publicly  
available server, the peers can sync without being online at the same  
time.

-Damien

>
> 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
> --
>