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> Is there a limit to the number of LVS nodes that can exist in a cluster?
> Some products promote that they are limited to 32, but I don't know where
> they came up with this.
Joseph mentioned that I've had LVS up and running with over one thousand
virtual servers. I had basically four class-Cs of virtual servers which were
loadbalanced through a LinuxDirector (two, actually -- I used redundant
directors) onto four real servers which each had the four different class-Cs
aliased on them. The four real servers answered queries for a number of
different services on each virtual server.
By "node" are you referring to the real servers or are you referring to the
virtual servers?
Either way -- in order for me to do all of the load balancing that I did, it
took a GREAT number of LVS rules. As far as LVS was concerned, I could have
been load balancing onto thousands of different machines rather than just
the four I was using.
I'm guessing that the limitation to which you are referring (32 nodes)
probably has something to do with the particular capacity of those products.
For example, a LocalDirector is going to have much less memory than say a
BIG/ip or an LVS. Every BIG/ip is going to be limited just because it's not
as scalable as an LVS.
Really LVS is a lot like a routing tool. If your system can handle it, LVS
is probably going to handle it. For example, you're not going to want to run
thousands and thousands of virtual server nodes using masquerading, but
that's perfectly fine to do using tunneling or direct routing.
Now back in the old days before Wensong expected anyone to need as many
virtual servers as I did, there were some small problems with ipvsadm that
simply had to do with dumping too much data into a buffer because the buffer
size wasn't being checked, but that's hardly a "limitation," that's just an
oversight. All of those problems have been sanded out.
> My first thought was that you were limited by your subnet addressing,
> but that really isn't a limit where you can document a number.
> Also; has anyone tried setting up a real server as yet another LVS
> router to more real servers? It strikes me that if this works, then
> you have no node number limits.
Reading this I'm guessing that by "node" you WERE referring to real servers.
a) I really think that LVS will handle as many nodes as you want AS LONG AS
YOU HAVE THE MEMORY TO DO SO
b) I'm sure that you could setup a chain of LVS servers like you're saying.
It wouldn't be difficult to do... The only trouble is that it would increase
latency. I don't know if it would be worth the trouble...
PLUS -- it would make managing your cluster a much bigger pain, I think.
All the best --
Ted
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