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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: multi-tenant web app
Date Wed, 17 Apr 2013 17:54:16 GMT
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Jamie,

On 4/17/13 1:28 PM, Jamie wrote:
> Dear Tomcat Users
> 
> Forgive me for saying this (and unless I am still misinformed
> after scouring the Internet for a solution), the Tomcat app server
> seems wholly inadequate for the demands of modern multi-tenant
> SAAS applications. Multi-tenant SAAS apps are supposed to be light
> weight and have the ability to scale. Sure, you can implement
> multi-tenant features inside the web app, but it makes sense that
> the functionality should be provided as part of the app server. The
> current business of deploying separate WARs is not
> practical/efficient for multi tenant use. We should be able to
> simply flag a context as multi instance. The instances should under
> the same classloader in a very light weight fashion.
> 
> Is there any chance the Tomcat dev team would look into adding
> this?

This can already be done with the common or shared classloaders (which
were removed by default because nobody could make head or tail of how
to use them properly). They can be trivially re-enabled using
conf/catalina.properties.

Note however that there are a whole slew of potential severe problems
with simply playing ClassLoader games:

1. You likely can't have a different version of library X for one
single tenant (you can put it into WEB-INF/lib but it might not be
visible from the right place and/or might conflict badly with the
shared library)

2. Any shared data in the libraries themselves can allow information
to leak from one tenant to another.

So, your webapp itself does have to have some measure of multi-tenancy
awareness. Multi-tenancy isn't just something you can slip-in at the
infrastructure-level.

- -chris
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