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From Aur Gal <>
Subject RE: Session management and scaleability
Date Thu, 19 Oct 2000 16:12:36 GMT
thanks, sorry for sending it twice.

-----Original Message-----
From: Colin Sampaleanu []
Sent: Thursday, October 19, 2000 10:58 AM
To: ''
Subject: RE: Session management and scaleability

Some servlet engines such as Resin's, WebLogic's, WebSphere's, ATG Dynamo's,
and if I remember Orion's, among others, include support for distributed
sessions. The best scaling mechanism I have seen is something such as what
Dynamo or WebLogic uses, which is to come in through the 'web server to
servlet engine connector' (which typically has to be there anyways), and
have that connecter always redirect the same session back to the same
servlet server. That servlet server then backs up session data in-memory to
only _one_ secondary servlet engine, which would take over in the case of a
failure of the first, and become the primary, with a new secondary (the
connecter would detected the failure and switch over automatically). This
scales really well since session data only has to be backed up to one other
machine, in memory. Other schemes such as what WebSphere 3.0 and older
versions of WebLogic used are to back up sessions to the filesystem or via
JDBC to a database. This works, and allows any of the servlet engines to
access session data, but is much slower.

In any case, this is all transparent to a load balancer, which is unaware of
what is going on. The load balancer hands off incoming requests to any one
of the web servers, and the connector on the web server then either hands
off requests to a random (or least used, whatever) servlet engine if the
session is new or being back up to the filesystem or JDBC), or to the
original servlet engine that handled the session creation, if the
primary/secondary scheme is being used.

> -----Original Message-----
> From: Aur Gal []
> Sent: October 19, 2000 10:55 AM
> To: ''
> Subject: Session management and scaleability
> Since struts defaults to using sessions and since it makes 
> developement much
> easier and faster. Is there any way that this type of session 
> management
> could be upscaled to a load balancer? for examle, is there any way to
> specify that all sessions should be stored and retrieved from 
> a particular
> server (database server, file server, etc..)? 
> thanks,
> Aur Gal
> Dove Solutions
> 515-469-5877 x126

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