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From "Costin Manolache" <cos...@gmail.com>
Subject Re: Osgifing Tomcat
Date Fri, 25 Apr 2008 18:37:19 GMT
On Fri, Apr 25, 2008 at 12:49 AM, David Jencks <david_jencks@yahoo.com> wrote:
>
>  On Apr 24, 2008, at 11:11 PM, Henri Gomez wrote:
>
>
> >
> > > I've heard various claims of this nature from osgi zealots, but when
> > > talking to apparent experts the only things resembling this they seemed
> to
> > > know about were grad student experiments that did not have production
> use as
> > > even a far-in-the-future goal.  Do you know of any actual examples of
> this
> > > kind of behavior that actually work under load?
> > >
> >
> > We'll see how OSGI works underload with Glassfish v3.
> >
>
>  Are they planning to support "gapless" redeployment of web apps using only
> osgi features, with no other servlet container support?  If so is can you
> point to an explanation of how they plan to do this?

There are many problems to solve for 'gapless' redeployment, but I
think the biggest is
sessions and statics. The classloader ( OSGI or not ) can keep
multiple versions of
the application loaded - but you need the mapper to know where to send
each request.
In theory it could be done even with the current tomcat, by including
the version in the cookie and changing the mapper to use it.

But I think the main question is if it's worth it - there is a lot of
complexity and many things that can go wrong. Very few advanced users
will be able to use this - in particular if they have production
environments and some release testing is required ( i.e. it would be
quite hard to automate and test what will happen in gapless case). The
alternative - having multiple machines/VMs running different versions
behind a load balancer - is quite safe and I suspect the 'advanced
users' who may need gapless would be better off using the old way.
I mean - if you run your app out of a single VM, probably you won't
need gapless, and if you already have load balancing/failover/multiple
servers - you have a better/safer solution.

Costin

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