[Zope3-dev] Some thoughts on Zope 3, Zope 3 applications, and Zope 3 instances

[Dieter Maurer]

Jim Fulton wrote at 2007-1-3 17:12 -0500:
> ....
>There will be an instance recipe that can generate instances that use  
>applications.  In a (Unix) production deployment, these instances  
>will have their files spread around more or less according to http:// 
>www.pathname.com/fhs/.  There won't be an instance directory.  For  
>development, instances will probably still be directories, but will  
>be much smaller and shallower than those produced by the existing  
>mkzopeinstance.  They will probably have a zope.conf files and  
>control scripts and their directories will also contain log and  
>zdaemon socket files.

Configuration files, too, share many common parts across instances.

Of course, you may say that these parts belong in fact to the
application and not the instances. However, I am unsure whether
e.g. the size of (general) caches or the available servers
(HTTP, FTP, ...) should be considered application specific.

We avoid this duplication in "ZConfig" configuration files
by two "ZConfig" extensions (submitted to the collector a long time
ago): a "%redefine" directive (to override common defaults by
instance specific definitions) and a "$(function arg1, arg2, ...)"
function call interpolation. We use the "env" function to access
definitions in the process environment.

These two extensions allow us to put common configuration files
under version control and reuse them across instances.
If necessary, an instance can use "%redefine" or define envvars
to override values in the common configuration file as necessary.



-- 
Dieter