class invocation conflicts

[Peter Berghold]

So here I am I have a base profile for my Ubuntu (Debian family) machines that invokes the class 

class{'apt':

    ... some paramters

}

I then invoke the class 

class{'postgresql': } 

and now Puppet is screaming that the class 'apt' cannot be invoked twice.   This seems to be a flaw in Puppet manifests to me.  How to fix?

--

Peter L. Berghold                       Salty....@gmail.com

http://devops.berghold.net

[Henrik Lindberg]

On 2019-05-20 18:57, Peter Berghold wrote:
> So here I am I have a base profile for my Ubuntu (Debian family)
> machines that invokes the class
>
> class{'apt':
>     ... some paramters
> }
>
> I then invoke the class
>
> class{'postgresql': }
>
> and now Puppet is screaming that the class 'apt' cannot be invoked
> twice.   This seems to be a flaw in Puppet manifests to me.  How to fix?
>
>

The best practice is to not use the resource like `class { name: ... }`
syntax to declare a class and instead use `include name` and letting all
parameter values come from hiera via automatic parameter lookup.

That way, you can include the class as many times as you like - as the
parameters are the same every time. Unfortunately, the compiler cannot
do the same when classes are declared with parameters even if all places
this is done use the exact same values.

While it is possible to have a single `class { name: ... }` declaration
with subsequent `include name` declarations, the opposite does not work.

Hope this helps.
- henrik

> --
>
> Peter L. Berghold Salty....@gmail.com <mailto:Salty....@gmail.com>
>
> http://devops.berghold.net
>
>
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[Peter Berghold]

Using include instead of class makes sense to me and was my instinctive thought.

Why on earth, then, do all the (or most) of the Puppet Forge modules use the 

class{'myclass':

    param1 => 'thing'

} 

patterns in their examples.  I had begun to believe that was the preferred pattern. 

I will mend my ways. 

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--

[Rob Nelson]

Most likely because that’s an easy way to show the parameters a class supports. Some modules use hiera data to show that, though it is a bit more complicated to explain and understand, especially for novices.

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Rob Nelson