Puppet users - Feb 2011 - reusing variables "best practices"

Hi All,

I''m in the process of creating Puppet modules for my load balanced
environment.  I have multiple Apache nodes behind a load balancer and each
Apache virtual host has its own internal IP.  I''ve created an Apache
module
that does this by creating an Apache vhost template and define my own
variables that are substituted by variables I''ve defined in my nodes
configuration. E.g.

apache1 node.pp:
$ip_www = 10.0.0.1
$ip_www2  10.0.0.1

apache2 node.pp:
$ip_www = 10.0.0.1
$ip_www2  10.0.0.1

apache vhost template:
<VirtualHost <%= ip_www %>:80>

The next step is to configure Piranha using Puppet.  The module creates a
template using the IP''s defined in my node configuration.  In order to
use
the IP''s I''ve defined in the nodes config file for the piranha
configuration
I''d need to rename the variables to something like:

$apache1_ip_www = 10.0.0.2
$apache1_ip_www2  10.0.0.2

As you can see if change the variable names to reflect the node name then
the Apache vhost template will not be generated correctly.

My question is what is the "best practise" when doing something like
this?
I was thinking of creating a new file for each apache node and write an
"if"
statement to include the appropriate file.  Another option would be to put a
case statement in the Apache module that if, for example, the nodes name is
apache2 then set $ip_www as $apache1_ip_www.
The part that I''m "concerned about" is how to redefine
variables to make
them compatible with both modules and perhaps future modules.  I hope this
all makes sense.

Thanks,
Gareth

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> The next step is to configure Piranha using Puppet.  The module creates
> a template using the IP''s defined in my node configuration.  In
order to
> use the IP''s I''ve defined in the nodes config file for
the piranha
> configuration I''d need to rename the variables to something like:
> 
> $apache1_ip_www = 10.0.0.2
> $apache1_ip_www2  10.0.0.2
> 
> As you can see if change the variable names to reflect the node name
> then the Apache vhost template will not be generated correctly. 
> 
> My question is what is the "best practise" when doing something
like
> this?  I was thinking of creating a new file for each apache node and
> write an "if" statement to include the appropriate file.  Another
option
> would be to put a case statement in the Apache module that if, for
> example, the nodes name is apache2 then set $ip_www as $apache1_ip_www.
> The part that I''m "concerned about" is how to redefine
variables to make
> them compatible with both modules and perhaps future modules.  I hope
> this all makes sense.
Not really ;-)

Do I read this correctly? You have two templates that are not generally
related, but rely on the same basic facts (i.e., a per-node IP-address
dedicated to Apache instances)?

What I''d do is (very near the definition of your "new"
template)

$apache1_ip_www = $ip_www
$apache1_ip_www2 = $ip_www2

By the way, have you checked whether the $ipaddress fact produces the
correct address for you? Because it would be several orders of magnitude
cleaner, more readable and more maintainable than inventing your custom
variables. You may even want to add a custom fact instead, if 10.0.0.2
is in fact not the primary address of your node.

HTH,
Felix

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