Puppet users - May 2013 - optional defined type and dependencies

Hi everybody,

I''m a new puppet user, and I have a question about defined types and 
relationships.

I want a defined type to be part of a module.
It manages optional configuration files, so the user can decide to declare 
it one or more times or not to declare it at all.
In the case the defined type is declared, I want the contained resources to 
be in relationship with other resources in my main module class; in 
particular, I want the resources in the defined type to be managed *after* 
package and *before* service.

Two ways come to mind:
1) embed the necessary require/before (and/or subscribe/notify) inside the 
the defined type''s resources:

# == Define: software::mydefinedtype
define software::mydefinedtype {
  file { "/path/to/${name}":
    [...]
    require => Package[''software''],
    before  => Service[''software''],
  }
}

2) rely on dependency chains and a resource collector in the main module 
class (and of course on the containment properties of defined types):

# == Class: software
class software {
  [...]
  Package[''software''] -> Software::Mydefinedtype <|
|> ->
Service[''software'']
}

What is, in your opinion, the best method?
I''ve tried both, and both apparently work with no issues.

One doubt about method 2:
at http://docs.puppetlabs.com/puppet/3/reference/lang_relationships.html, I 
can read:
"If one of the resources in a relationship is never declared, compilation 
will fail with one of the following errors [...]"
I suppose that this doesn''t apply in case of resources chained through 
resource collectors, does it? I''m asking because, even without
declarations
of instances of the defined type, I got no such errors.

Thanks a lot for your help!

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On Wednesday, May 29, 2013 10:29:22 AM UTC-5, Fabio Sangiovanni
wrote:
>
> Hi everybody,
>
> I''m a new puppet user, and I have a question about defined types
and
> relationships.
>
> I want a defined type to be part of a module.
> It manages optional configuration files, so the user can decide to declare 
> it one or more times or not to declare it at all.
> In the case the defined type is declared, I want the contained resources 
> to be in relationship with other resources in my main module class; in 
> particular, I want the resources in the defined type to be managed *after* 
> package and *before* service.
>
> Two ways come to mind:
> 1) embed the necessary require/before (and/or subscribe/notify) inside the 
> the defined type''s resources:
>
> # == Define: software::mydefinedtype
> define software::mydefinedtype {
>   file { "/path/to/${name}":
>     [...]
>     require => Package[''software''],
>     before  => Service[''software''],
>   }
> }
>
> 2) rely on dependency chains and a resource collector in the main module 
> class (and of course on the containment properties of defined types):
>
> # == Class: software
> class software {
>   [...]
>   Package[''software''] -> Software::Mydefinedtype <|
|> ->
> Service[''software'']
> }
>
> What is, in your opinion, the best method?
> I''ve tried both, and both apparently work with no issues.
>

For this particular pattern of requirements, I strongly prefer method 1.  
It keeps everything associated directly with the defined type together in 
one place.  I would suggest one tweak, however: the defined type should 
explicitly ''include'' class ''software'' if it
refers to resources declared by
that class.  For example:

define software::mydefinedtype {
  include ''software''
  file { "/path/to/${name}":
    [...]
    require => Package[''software''],
    before  => Service[''software''],
  }
}

Note also that if you prefer the chain operators to the metaparameters, you 
can use the former in your defined type:

define software::mydefinedtype {
  include ''software''
  file { "/path/to/${name}":
    [...]
  }
    Package[''software''] ->
File["/path/to/${name}"] -> Service[''software'']
}
 
Indeed, I think you can even write it like this:

define software::mydefinedtype {
  include ''software''
  Package[''software''] -> 
  file { "/path/to/${name}":
    [...]
  } ->
  Service[''software'']
}


> One doubt about method 2:
> at http://docs.puppetlabs.com/puppet/3/reference/lang_relationships.html, 
> I can read:
> "If one of the resources in a relationship is never declared,
compilation
> will fail with one of the following errors [...]"
> I suppose that this doesn''t apply in case of resources chained
through
> resource collectors, does it? I''m asking because, even without
declarations
> of instances of the defined type, I got no such errors.
>
>
Personally, I am uncomfortable with relying on undocumented behavior.  It 
may change without warning from one version of the software to another.  
Even if that does not bother you, in this particular case you should also 
verify that the transitively implied relationship between 
Package[''software''] and Service[''software'']
is still present when no
instances of Software::Mydefinedtype are declared.  You can make puppet 
generate a relationship graph to check.


John

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Hi, thanks for your answer.

On Thursday, May 30, 2013 3:13:45 PM UTC+2, jcbollinger
wrote:
>
>
> For this particular pattern of requirements, I strongly prefer method 1.  
> It keeps everything associated directly with the defined type together in 
> one place.  I would suggest one tweak, however: the defined type should 
> explicitly ''include'' class ''software''
if it refers to resources declared by
> that class.  For example:
>
> define software::mydefinedtype {
>   include ''software''
>   file { "/path/to/${name}":
>     [...]
>     require => Package[''software''],
>     before  => Service[''software''],
>   }
> }
>
Yes, that''s what I actually did in the end. And I''ve also used
the include,
as you suggested (I didn''t post my whole code in the first post, just
the
relevant part).

Note also that if you prefer the chain operators to the metaparameters, you
> can use the former in your defined type:
>
> define software::mydefinedtype {
>   include ''software''
>   file { "/path/to/${name}":
>     [...]
>   }
>     Package[''software''] ->
File["/path/to/${name}"] -> Service[''software'']
> }
>  
> Indeed, I think you can even write it like this:
>
> define software::mydefinedtype {
>   include ''software''
>   Package[''software''] -> 
>   file { "/path/to/${name}":
>     [...]
>   } ->
>   Service[''software'']
> }
>
>  
Clever! Thanks :) 
 
>
>> One doubt about method 2:
>> at
http://docs.puppetlabs.com/puppet/3/reference/lang_relationships.html,
>> I can read:
>> "If one of the resources in a relationship is never declared,
compilation
>> will fail with one of the following errors [...]"
>> I suppose that this doesn''t apply in case of resources chained
through
>> resource collectors, does it? I''m asking because, even without
declarations
>> of instances of the defined type, I got no such errors.
>>
>>
>
> Personally, I am uncomfortable with relying on undocumented behavior.  It 
> may change without warning from one version of the software to another.  
> Even if that does not bother you, in this particular case you should also 
> verify that the transitively implied relationship between 
> Package[''software''] and
Service[''software''] is still present when no
> instances of Software::Mydefinedtype are declared.  You can make puppet 
> generate a relationship graph to check.
>
I avoided the issue too, I''ll try to generate the graphs as soon as I
have
some spare time. 
>
> John
>
 
Thanks again,

Fabio

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There''s a third way, too. In the defined type''s definition:

define software::mydefinedtype {
  include software
  Package[''software''] -> Software::Mydefinedtype[$title]
  ...
  ...etc.
}

That creates a relationship between the package and every resource in each 
instance of the defined type. Every instance you declare will create its 
own relationships.

This approach has the concision of the second example you were considering, 
but works more like the first example.

Also:

>
> One doubt about method 2:
> at http://docs.puppetlabs.com/puppet/3/reference/lang_relationships.html, 
> I can read:
> "If one of the resources in a relationship is never declared,
compilation
> will fail with one of the following errors [...]"
> I suppose that this doesn''t apply in case of resources chained
through
> resource collectors, does it? I''m asking because, even without
declarations
> of instances of the defined type, I got no such errors.
>
Yeah, with a collector that doesn''t catch anything, a chaining
statement
won''t create any relationships, and shouldn''t blow up.

N 

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