Scaling of ctdb & DNS round robin and scaling of pdc

[ronnie sahlberg]

Use LVS for loadbalancing.
Then clients are guaranteed that all sessions will go to the same node.

It will avoid a lot of the nastiness and failure modes you have in
RRDNS.  Maybe we should
update the wiki to recommend using LVS instead ?


On Sat, Oct 27, 2012 at 1:56 AM, Martin Schwenke <martin at meltin.net> wrote:
> On Thu, 25 Oct 2012 10:28:55 +0200, Johannes Amorosa | Celluloid VFX
> <johannesa at celluloid-vfx.com> wrote:
>
> I haven't seen anyone answer this question directly so I'll make a best
> guess and people can correct me...  :-)
>
>> 1. In the ctdb wiki http://wiki.samba.org/index.php/CTDB_Setup it is
>> recommended to use dns round robin for loadbalancing.
>> I'm quite new to this - how does samba handle a "session". We need
>> massive I/O for our setup and considering ctdb to avoid our
>> smb bottleneck. When is the client getting a "different" IP- Address?
>> Everytime a file is read or stored - our every morning when
>> you log into your workstation. If this is the case then loadbalancing
>> would be quite random.
>
> The closest answer is that a client will get a different IP address
> when logging into a workstation.  I say "closest" because it doesn't
> occur on a per-file basis but I have seen some situations where clients
> have connections to multiple nodes.  Samba experts might be able to
> explain this more clearly.
>
> Yes, round-robin DNS based load balancing is quite a weak form of load
> balancing because it doesn't take into account the actual load on the
> nodes.  However, if you have a lot of clients then it can average
> out so it looks like some of the clever forms of load balancing.  :-)
>
>> The scaling figures in one of the PDFs are impressive - are these
>> "artifical" benchmark tests or real life scaling?
>
> You would probably have to tell us which PDF!  Some of the documents
> are pretty old so we would have to find someone who remembers, but
> performance has improved over the years rather than degrading.  CTDB is
> used to effectively cluster Samba in many places...
>
> peace & happiness,
> martin