> Ramani wrote:
> > Has anyone here tried load balancing/fault tolerance with servlets. More
> > specifically, in a JRUN environment ? The servlet based application will
> > be creating HttpSessions. So the issue would be how the sessions could
> > be tracked on all the instances of the servlet engine
David Mossakowski (dmoss@instinet) replied:
> JRUN has no near-future plans to add load balancing across its engines. Check
> Foundry Networks, F5 and Cisco for solutions.
>
> I would too like to know of a servlet application working with load balancing
> (across geographic locations too).
Hm, well, it occurs to me that there are some dodges you could
use to get this in effect. The question would be, are they be worth
the trouble (i.e. would the overhead of sharing cancel out the gain of
load balancing)? Essentially it would involve setting up some sort of
external HttpSession server and having the servlets use that instead
of the HttpSession stuff built into the jrun server.
The external HttpSession server wouldn't be running in the same
JVM, so the servlet would have to have maybe an RMI connection open to
it. Would the overhead wf the RMI connection outweigh the
load-balancing gains?
And is it sufficient to have a single, shared HttpSession server
(maybe even just a third webserver with Jrun), or would you have to
build some sort of distributed HttpSession server? If not, you could
do something clever where the JRUN HttpSession mechanism uses some
sort of key that includes a server-specificID (to avoid identical
session IDs being issued by separate servers), and add an HttpSession
factory that checks the local HttpSession first, and if not available,
polls the other Jrun servers, but the work involved starts to add
up...
If the answer to either of the above two questions is yes, then
it starts to look like it's worth getting an EJB environment or other
servlet engine that provides the load balancing.
Steven J. Owens
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