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From Pid <>
Subject Re: Clustering / High Availability edge cases?
Date Tue, 13 Sep 2011 21:42:47 GMT
On 13/09/2011 10:51, John Bass wrote:
> Hi all,
> I'm relatively new to clustering with Tomcat and I'm trying to understand
> the edge cases.  If I'd like to guarantee continuous availability, what are
> the caveats?
> As I understand it, Tomcat clustering will ensure that session information
> is persisted in the event of a failure.  That's fine, however, what about
> long running I/O operations?

Operations relating to the session, or something else?

> What if my node dies in the middle of serving an HTTP response?  

Well, the point to point connection will be severed, so an error will
likely occur in the client.  This is not an issue unique to Tomcat.

> In the event of a node failure, I'm assuming that there's
> no way to recover from that and the failure will be visible to a client
> application.

Depends what the client & node are doing at the time & whether there's
anything in between them (e.g. a proxy).

> Similarly, if a node fails during a long running calculation, I'm assuming
> that there's no way to persist that execution state.

Again, not a Tomcat specific problem.


> Are those assumptions correct?  If anyone has any other comments on further
> scenarios where clustering and session persistence will not be useful in an
> HA context, i'd love to hear them.
> thanks,
> John

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