[Puppet Users] How to refer to common variables across multiple modules?

The idea of putting the shared data in a class (or classes) is very
reasonable. You might consider, however, assigning them to classes
specific to their purpose. For example, supposing that you will eventually
want to manage your firewall via Puppet, you should consider whether it
makes more sense to put the $fw_ip variable in a class associated
specifically with that instead of in a general-purpose common class.

It is potentially problematic, however, that you feed the shared data to
your classes as class parameter defaults. It will probably work with the
ENC-based setup you describe, but it has parse-order dependencies arising
from usage of class 'common's variables by classes that themselves do
nothing to ensure that class common has yet been evaluated. In particular,
the chaining operators do not help: they set up client-side
order-of-application constraints, but do not constrain compile-time
order-of-evaluation.

I have never been a big fan of class parameterization, and I don't see what
it's actually doing for you here. Yes, it gives you a hypothetical ability
to override the shared data on a per-class basis, but do you actually need
that right now? It complicates your work, and if you don't need it now
then there's a good chance that you're not ever going to need it. I would
write the classes along these lines:

class apache {
   include 'common'
   # use $common::fw_ip, etc. explicitly, as needed
}

Or if you want to provide for easy insertion of per-class overrides in the
future, then it would be cheap and mostly harmless to do it this way:

class apache {
   include 'common'
   $fw_ip = $common::fw_ip

   # use $[apache::]fw_ip, as needed
}

There are other alternatives, such as variations on the theme of loading
the wanted data from an external store (e.g. hiera) instead of having the
ENC specify them. All in all, you seem to be thinking about the right
issues.


John

You might consider Top Scope [1] and/or Node Scope [2] variables.

[1] http://docs.puppetlabs.com/puppet/3/reference/lang_scope.html#top-scope
[2] http://docs.puppetlabs.com/puppet/3/reference/lang_scope.html#node-scope

I've found that using Hiera for this type of problem work's really well.
Hiera is integrated into Puppet 3.0+

https://github.com/puppetlabs/hiera


Drew