I was planning to use a simple http redirect from the primary site, to the
nearest local site, using info in the request header. At each site I have
several servers, some running tomcat, some running apache and tomcat. I have
several issues I need to address:
- The JSP's are fairly intensive and experience shows that I need
- I would like to be able to avoid redirecting to a site that has no
webserver, even if the machine is available.
- Authenticated User sessions should be sticky WRT to servlet engine
- Users like a single address for access to the site.
- The servers are 'cheap' hardware that can fail
- I have servers in multiple datacentres within a MAN. The Links are
high speed, but multicast access is restricted
- If I lose a whole location ( e.g. LDN ) I want to fall over to
another location seamlessly
- Some requests make sense to be executed in specific regional
centers for access to local data
Today I use mod_jk for loadbalancing the work and keeping sessions together.
I assign a weighting for load at startup time, and use a statistical
round-robin algorithm to 'spread' the requests. Server and site failure are
dealt with manually.
I am trying to workout if spending time in learning how to use mod_backhand
etc will offer me a good return on investment, and seek a jump start into
the process through the good people on this mailing list
Thanks for the encouragement
From: Theo Schlossnagle [mailto:email@example.com]
Sent: Thursday, April 25, 2002 3:56 PM
Subject: Re: [m_b_users] Newbie question: Loadbalancing Apache and
Weir, John wrote: >I am a bit confused:-( sorry for being dumb.
>With Apache and Tomcat, I use mod_jk to loadbalance jsp requests across
>multiple servlet engines. This works well. If I replace mod_jk, with
>mod_backhand, would it be better to loadbalance requests across multiple
>Apaches, with each Apache associated with a single tomcat servlet engine,
>and as Yair suggests use an alternative strategy to route requests
>Anyone got experience of this? If so, I'd really appreciate a look at a
>sample config file and any tips that you may have.
>Thanks in advance
Asking questions about how to best accomplish your goals is seldom dumb
and often many people benefit from observing the conversation on these
mailing lists. However, I didn't really get a good feeling for your goals.
Do you need to load-balancing globally? Is it really likely at all that
one geographic location could get so overloaded that you would want to
push someone to another geographic location? If so, you will want to
use some sort of resource monitoring on the clusters to make these
decisions and redirect people based on that information. mod_backhand
can do this.
If, on the other hand, you simply want people in the americas to go to
your SJC datacenter, Eurpoe to go to your LDN datacenter and the far
east to go to your TKY datacenter, then you aren't looking for load
balancing. You are looking for a service resolution protocol. DNS
works, but wasn't designed for this. There are a few papers and even
fewer implementations that can give you the result you are looking for
-- but they exist. Yair referenced a paper already.
UltraDNS (www.ultradns.net) can help you out with this. They have an
implementation of a global DNS system that can return different IPs
based on the location of the requestor. (effectively finding the closest
I think you need to sit down and clearly define the business
requirements of the system. If it is a large system, it stand to
reason, there will be some money in it... You should probably hire a
consultant to review your goals and your proposed implementation. It is
good to use someone who has done this before as a sounding board. Saves
time. Saves money.
OmniTI Computer Consulting, Inc. -- http://www.omniti.com/
Phone: +1 301 776 6376 Fax: +1 410 880 4879
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