Hi Len,
the normal servlet spec conform purpose is to handle administration
down, app version migration or
handle real crashes without lost your user session/context! This
means not that tomcat replication cluster can't handle your "request
stateless" szenario. It works
with speziell application, but to build those application is a very
hard job. You can test it with pooled replication mode, but it's high
risk to have inconsistence at normal runtime. You must have good
synchronization points to handle multiple request at same session at
lots of threads and processes. Please, check how your browser client
interact exactly with your application. At my experience the sticky
session constraint help to have a better and controlled server env :-)
Peter
Am 03.11.2007 um 16:16 schrieb Len Popp:
But isn't the purpose of session replication to allow different
servers to handle the session? If not, what's it for?
--
Len
On 11/3/07, Peter Rossbach <[EMAIL PROTECTED]> wrote:
Hi,
It is not only ineffizient and a risk, Read 7.7.2 at the spec:
SRV.7.7.2 Distributed Environments
Within an application marked as distributable, all requests that are
part of a session
must be handled by one Java Virtual Machine1 ("JVM") at a time. The
container
must be able to handle all objects placed into instances of the
HttpSession class
using the setAttribute or putValue methods appropriately.
....
regards
Peter
Am 02.11.2007 um 22:37 schrieb Len Popp:
You can indeed use session replication without sticky sessions, and
the session data will be copied to all the Tomcat servers.
However it
may be inefficient. You probably have to use synchronous replication
to ensure the session data is consistent across the cluster, which
adds latency to the requests. And there could be a lot of extra
network traffic in the cluster if it's busy (which it is, otherwise
you wouldn't be doing load balancing).
(I haven't used session replication in a high-load situation. Maybe
someone else can tell us how well it works.)
--
Len
On 11/2/07, Stephen Wick <[EMAIL PROTECTED]> wrote:
The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make
sure
that your loadbalancer is configured for sticky session mode."
However,
I don't see the term "Sticky" sessions anywhere in the Servlet
2.3 or
2.4 specifications.
Are sticky sessions really required for clustering to function
properly
in Tomcat 5.5? I thought that session replication would eliminate
any
need to direct a client session to one node in a cluster.
If not, can we adjust the documentation to indicate that Sticky
sessions
are optional, for the appropriate reason (I'm guessing the
advent of
session replication in tomcat.)
I am asking this question because I am having trouble with Sticky
sessions in my load balancer, and I need to know whether or not I
should
pursue fixing this feature. If tomcat doesn't really require
sticky
sessions, then I can leave my load balancer alone. If tomcat does
need
the feature to function properly, then I need to go to some
additional
expense to resolve the issue with my load balancing appliance.
Thank you for your time and expertise.
Stephen Wick
Interactive Developer
Nicholson Kovac, Inc.
References
http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
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