On Apr 3, 2009, at 4:31 PM, MSP wrote:
On Apr 3, 4:11 pm, Chris Buxton <cbux...@menandmice.com> wrote:
Using DNS, I want to do load balancing of client requests among my
available servers dynamically.
In realtime requirements, any/many servers among the configured me
be
down or overloaded.
I want to have control over distribution of load to these servers. I
want to have a common FQDN to the clients and they know only FQDN. I
would like to have 10/20 servers handling the client requests. When
ever a server goes down, all the requests (thousands) it was
handling,
should come to remaining available servers quickly (assume within
few
seconds).
I feel we can use DNS for this purpose, but doing load balance in
realtime?
I don't believe you will be successful at this with just DNS. The
problem is that you want client connections switched over in case
of a
server failure. My understanding is that web browsers will not honor
your TTL's. (This is how it was the last time I operated a production
web server cluster, back in medieval times. I don't see why things
would have changed.)
What you need is a load balancing solution at the HTTP level.
Preferably more than one, such that the devices can share an IP
together in some kind of fault-tolerant way.
Either way, if it were me, I would start my search at the F5
website.http://www.f5.com/solutions/availability/
Chris Buxton
Professional Services
Men & Mice
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Hi Chris,
I have these servers located on the same system (paraller processing
- loosely coupled). I will know the load on these servers at realtime
and for new connections, I want to do proper load balance. Basically,
I want to send least loaded server IP address in the DNS response so
that the new client connection goes to the least loaded server. And if
any server goes down, my client application will do DNS query and I
will distribute these new connections among available servers.
This sollution which I am thinking is for some telecom application and
not for web browsers.
I kown that TTL for my requirement should be ZERO, so that no cashing
happens.
Please tell why we can not use DNS sollution for this.
Because browsers cache DNS results, often ignoring TTL's. In my
(admittedly ancient) experience, browsers would cache the last x
number of DNS results they got, where x was something like 50 or 100.
And a result to be cached was equal to the first IP address in the DNS
result - all other data was discarded.
Therefore, if one server of your cluster goes down, connections don't
switch to other available servers. They just fail.
Now IE 7 and later, I have been told, behaves differently. But I
believe other browsers still behave this way.
DNS-based load balancing, in my experience, is not up to the demanding
task you have in mind.
Chris Buxton
Professional Services
Men & Mice
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