Georg Henzler created JCRVLT-254:
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             Summary: Support content filtering with environment variables  
                 Key: JCRVLT-254
                 URL: https://issues.apache.org/jira/browse/JCRVLT-254
             Project: Jackrabbit FileVault
          Issue Type: Bug
            Reporter: Georg Henzler


There are two use cases, where it would nice to have an option to "dynamically" 
adjust content upon installation time:
1. Replication Agents (or in a pure open source world: any content node 
properties that hold URI-references to external systems that might differ on 
environments or more generically, any content node properties that shall hold 
different values on different environments, e.g. on/off switches)
2. OSGi configurations: URLs to other systems (e.g. Stage->Stage/Prod->Prod 
Mappings)  Externaliser config etc., everything that we commonly do with run 
modes today

Today we solve this by
1. creating a package per environment, custom tools or manual configuration 
(worst case)
2. runmodes

When talking about cattle and not pets (having an at implementation time 
unknown magnitude of servers), the problem is that today's solution becomes 
fairly complex. 

The idea would be to allow system environment based rewrites of properties 
during package installation time (iff a package property is set to allow for 
this). This would be used sparsely/wisely to automatically set certain 
configuration options that cannot be known at implementation time (most OSGi 
configs would remain fixed according to runmodes that are roles, but for some 
this approach could be used). 

As a POC I created an install hook that does the same thing:
https://github.com/ghenzler/apply-system-env-install-hook
However the problem with this approach is that I cannot avoid saving a property 
twice - although the original values with variable placeholders will only be 
saved/active in the repo for ms, it will still trigger events (e.g. activating 
an OSGi config twice in a row, first with an incorrect value). I'm not aware of 
a way to use the INSTALL phase to modify the content in the package (I can read 
it, but not modify it I believe). This is way I would like to see this as a 
"first level citizen" in vault itself.






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