> I recently read a white paper about apache load balancing and fault
> tolerance, but I still have some questions about it.
>
> It says apache using DNS round robin to assign the actual IP to the server,
> how does this work?
yes.
> Does all the DNS server today support this?
yes
> Let's see I have two machines, A and B, with same name assigned by DNS. A
> client connection comes in, due to round robin, machine A gets pick up.
> Then subsequent call should always talk with A, shouldn't it? Now if A
> fails, what will happen to the client? Will it be connected to B? How?
that is why round robin dns doesn't work very well. ;-(
what you should have is a single machine with multiple jserv servlet engines
(ie: the java portion) on the back end. if one of the servlet engines goes
down, mod_jserv will figure that our and stop sending requests to it.
web client -----> apache -----> mod_jserv -----> servlet engine 2
|
|
v
servlet engine 1
if you need more redundancy on the front end machine, there are tricks that
you can do with multiple apache's proxying the information to other servers
as well as router tricks (check out www.packeteer.com...we have one on loan
here at clear ink and their boxes rock!).
for serious redundancy, you can also have another machine that is not
plugged in that can replace the "apache" portion of the diagram above by
simply changing some wires.
there are also quite a few other schemes out there...
-jon
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