You might need to think about the necessary aspects of your solution
first. Some of those might be:
- Necessity of High Availability, more precisely, amount of availability
needed (planned and unplanned downtimes, allowed planned downtimes, when
and how long and how much in before declared)
- Are services stateful or stateless, so can you actually use round
robin, or do users need to be rerouted to their origin node when doing
followup requests? Will you need session replication to enhance
availability, or would relogin be OK in case of node failure?
- Do you prefer management of load balancing by the network people, or
the server people or application. Which of those groups accept that they
have to build up some knowledge about the details of the mechanisms
involved?
- How many objects will need to be managed: 10 Tomcat instances, or 10
Tomcat nodes with 4 instances each with 5 very different webas per
instance ...
- Is SSL involved? Which layer should terminate SSL?
More questions than answers, but the questions are intended to give you
an idea, that there are not only simple technical issues when deciding
about this kind of global application architecture.
If you don't need HA, then you could start with a single lb, maybe with
a standby second one. If you need HA you'll need a pair and a network
layer construct, that ensures transparent failover.
Usually you also have stateful sessions, so you need to think about
stickyness. Often sessions are not very expensive for the customers, sou
you can start without replication.
Network appliances or Apache/mod_jk: This mostly depends on:
- which people (organisation, skills) should do the daily administration
concerning the balancing
- how are you going to implement HA
In case you consider mod_jk: there is also Apache 2.2 with
mod_proxy_balancer/mod_proxy_ajp. These modules will be fine for an easy
quickstart. In case you are planning to do more complex topologies,
timeouts etc., you might want to directly start with mod_jk (Disclaimer:
I'm writing code for mod_jk).
Regards,
Rainer
Asensio, Rodrigo wrote:
Hi, I'm planing to do load balancing on my 3 apache tomcat server.
Actually they are windows 2003, 5.5.23, ibm jdk 1.5.
I'm planing to put a linux in the front who balances the load for the 3
servers. I read about the issue and there are several solutions. This is
a small farm, maybe up to 10 servers in the very very future, will no
grow up more than that. Now, what do you recomend ? use a Apache mod_jk
in the front ? use the load balancer with a round robin rule ?
regards
R
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