This is my obsession :)
Foundry Networks and F5 both say they do 'sticky' sessions too. Check with them to
learn more on this. Also I the Global Director (as opposed to Local Director which is
too small) is really the way to go for an Internet app but it's a pain to set up and
administer.
dave.
Ari Senator wrote:
> Here is a scenario of an application that uses HttpSession and caches
> application data on that session which may encounter a serious
> problem due to the potential loss of the data on that HttpSession when using it
>with load balancing.
> A possible scenario is as following:
> 2 web servers A,B and a load balancer (local director ) C that balances requests
> made from browsers to the appropriate web server according to the load on each box.
> Say each web server capacity is 50 users and there are 50 users logged to server A.
>Due to some time-out (browser/transport layer) a user stops interacting with A and
>instead a subsequent user is assigned to A . When the original user that timed-out due
> to the transport layer tries to proceed his session (with possibly valid
>HttpSession) he is assigned to server B since A is in full capacity (50) .
> The user that may be in the middle of a transaction - expects to be able to proceed
>with the data that was cached on the HttpSession, yet, the user was assigned by the
>load balancer to a second web server (B) and therefore the HttpSession information is
>lost.
>
> Note: maintaining cached application information on the Httpsession enables saving
>many calls to the database to re-retrieve that data and therefore saves a substantial
>amount of time.
>
> The question: is there a way to force a load balancer to maintain a browser's
>session that started with a web server (as long as it didn't time-out due to the
>server session time-out ) to persist with that web server ?
> This persistence can expire when the user's HttpSession expires. (and the load
>balancer needs to know it so it can assign another user instead for that web server ).
>
> If this isn't possible how ,then , do applications that use session management
>overcome a load balancing "intervention" that may invalidate a session that a browser
> maintains with a web server ? if the user/broswer is re-routed to a different web
>server ?
> This must be a typical scenario in an application that uses session mgmt. and load
>balancing ...
>
> Thanks
> Ari
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Instinet Corporation
"I don't sit idly by, I'm planning a big surprise"
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