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 Posted: Sun Dec 10, 2006 7:37 pm |
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Greetings,
I'm investigating how to setup ejabberd for high availability. My
userbase will probably never exceed the capacity of a single machine, but
I need a jabber service that will have near 0 downtime (live failover, am
I dreaming here?) on a small budget.
So my current thought is to Linux Virtual Server and float a virtual IP
between two real servers (ejabberd nodes). Effectively, one cluster node
would always have all of the users on it, but that isn't a concern.
Looking through the docs I notice that mod_muc is not cluster friendly. I
definetely need MUC support, so will this be a show stopper for attempting
this setup?
Anybody have ideas / docs on the best way to approach this?
thanks!
daryl
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| Posted: Tue Dec 19, 2006 5:31 pm |
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On Sun, 10 Dec 2006, Daryl Herzmann wrote:
> Greetings,
>
> I'm investigating how to setup ejabberd for high availability. My userbase
> will probably never exceed the capacity of a single machine, but I need a
> jabber service that will have near 0 downtime (live failover, am I dreaming
> here?) on a small budget.
>
> So my current thought is to Linux Virtual Server and float a virtual IP
> between two real servers (ejabberd nodes). Effectively, one cluster node
> would always have all of the users on it, but that isn't a concern.
>
> Looking through the docs I notice that mod_muc is not cluster friendly. I
> definetely need MUC support, so will this be a show stopper for attempting
> this setup?
>
> Anybody have ideas / docs on the best way to approach this?
Hi, Anybody have comments? Am I missing something obvious?
thanks!
daryl
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| Posted: Wed Dec 20, 2006 6:19 pm |
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2006/12/19, Daryl Herzmann <akrherz@iastate.edu>:
> > Anybody have ideas / docs on the best way to approach this?
> Hi, Anybody have comments? Am I missing something obvious?
You may be missing this newspost, currently the second on ejabberd front page:
Fault-tolerant XMPP Environment Using Cisco Server Load Balancing
http://ejabberd.jabber.ru/cisco-slb
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| Posted: Wed Dec 20, 2006 8:37 pm |
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Badlop wrote:
> 2006/12/19, Daryl Herzmann <akrherz@iastate.edu>:
>> > Anybody have ideas / docs on the best way to approach this?
>> Hi, Anybody have comments? Am I missing something obvious?
> You may be missing this newspost, currently the second on ejabberd front
> page:
> Fault-tolerant XMPP Environment Using Cisco Server Load Balancing
> http://ejabberd.jabber.ru/cisco-slb
couple of comments...
First...Cisco is *EXPENSIVE*. If you're interested in a hardware
platform to do load-balancing, I can recommend F5 Networks' Big-IP
devices...we use them and they're quite nice, and considerably less
expensive than Cisco.
However, I think I can speak a little bit to Daryl's question, being
somewhat familiar with what he's doing with XMPP. First, I'm pretty
sure he doesn't need load balancing at all, though it might end up being
a nice bonus. I think the consideration is purely for High
Availability, with heavy emphasis on mod_muc.
So, let me contribute what I *think* is going to answer Daryl's
questions, with the caveat that I've never actually done any of this, so
I could get some of it wrong, but also with hopes that by posting this,
it will encourage others to jump in and correct where I'm wrong. 
The basic ejabberd server is clusterable to have multiple nodes act as
if they are a single server, so basic authentication and presence will
work as expected regardless of which node you connect to.
If you're connected to a node and it fails, then your connection will
get dropped (ie, no stateful fail-over of connections), but you could
then immediately reconnect to another node and go on about your business.
My understanding is that mod_muc is *not* a clusterable component, so if
you run mod_muc on two clustered nodes, you would end up with two
independant sets of chat-rooms. I'm presuming that two copies of
mod_muc would even start on the nodes with the same configurations...or
would it get started on one and the second one trying to start up result
in some sort of conflict with the first if they were trying to use the
same jid?
This may work for you, Daryl...
I'm guessing something like using Linux heartbeat to have a shared IP
address that will be active on one of the nodes. Having mod_muc,
configured the same, running on both nodes (again, assuming that they
won't fight over having the same jid in an otherwise clustered
situation), then, if the active server fails, everyone's connection will
get dropped, heartbeat fails over the shared IP address to the other
node, and when everyone reconnects, they rejoin the much chat-rooms on
the second node. The only thing you would lose is that the history in
the chat-room would be lost for people joining, but I think you're going
to lose that if your mod_muc gets restarted (whether as part of a full
server restart or just restarting mod_muc) anyway, so I don't think
you're any worse off for that.
So...if you ensure that *all* of the people connected to the server are
connected to only one of the nodes, do you really *need* mod_muc to be
clusterable? To take it a step farther, do you really need (other than
just for ease of management) any of ejabberd's clustering capabilities?
Perhaps not. *shrug*
--
Jeff McAdams
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor safety."
-- Benjamin Franklin
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| Posted: Sat Dec 23, 2006 12:22 am |
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Hi Jeff,
On Wed, 20 Dec 2006, Jeff McAdams wrote:
> However, I think I can speak a little bit to Daryl's question, being
> somewhat familiar with what he's doing with XMPP. First, I'm pretty
> sure he doesn't need load balancing at all, though it might end up being
> a nice bonus. I think the consideration is purely for High
> Availability, with heavy emphasis on mod_muc.
Correct. One machine can handle the load, I would really like to have
live failover not noticed by end-users.
> If you're connected to a node and it fails, then your connection will
> get dropped (ie, no stateful fail-over of connections), but you could
> then immediately reconnect to another node and go on about your
> business.
That isn't quite what I had hoped for, the reconnect step. Perhaps what I
am asking ejabberd to do is not possible.
> So...if you ensure that *all* of the people connected to the server are
> connected to only one of the nodes, do you really *need* mod_muc to be
> clusterable? To take it a step farther, do you really need (other than
> just for ease of management) any of ejabberd's clustering capabilities?
> Perhaps not. *shrug*
Agreed. Perhaps running two seperate, but identical setups with Linux
IPVS doing failover is what I need. A brief reconnect is not too much to
ask users to do
thanks!
daryl
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