How it Works Today

When a local instance is created, a new tree is created which is a copy of the global instance, and all of the CGIs and modules are symbolically linked to the global instance. This way, the global instance can be updated, and the local instance will get the changes, unless the local instance has modifications. A local instance is modified by breaking the symbolic link, i.e. copying the file to the local instance. This way local modifications can be made, with the tradeoff that global updates won't be seen. The CGIs use the local modules by modifying @INC to look in the local 'lib' diretory first.

Thus, all the CGIs and modules in all the instances use a module, which will be found in the local instance's include directory, but the module itself may or may not be a link to the global instance.

The example CGI would look like this:

#!perl
BEGIN { unshift @INC, "$ENV{LOCAL_INSTANCE}/lib"; }
use Some::Module;
# ...
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The Problem Using mod_perl

When we try to run this under mod_perl, the system breaks down. The first time a particular apache child gets called, it's compiled, and uses the module appropriate for the instance. But the next time it gets called, for possibly some other instance, it's still using the module that was compiled the first time. We need to the CGI to uise the module that is appropriate for the instance that it was caled for.

Solutions We Are Considering

• Run a separate Apache daemon for each instance, on a different port. One Apache will act as a Reverse Proxy and dispatch requests to the appropraite instance based on Location. Doesn't require changing the code, but doesn't seem like the right way to do it, and introduces more of a sysadmin problem.
• Use one Apache, and give all the modules an instance-based namespace when the instance is created. This means changing the modules' package statement to something like:

  package LOCAL_INSTANCE::Some::Module;
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  and changing the CGIs to use LOCAL_INSTANCE::Some::Module; as well as any statements that would have been something like my $obj = Some::Module->new etc. Also doesn't seem like the right way to do it, and requires major structural changes.

How You Can Help

Has anyone run into this sort of problem before, and come up with a workable solution?