Puppet users - Sep 2011 - Passing additional dependencies into a class

I''m using an Apache 2 base class based on
http://projects.puppetlabs.com/projects/1/wiki/Debian_Apache2_Recipe_Patterns.

I''d like to pass additional dependencies to the class and/or the
definitions
it contains. For example, I''d like to allow classes using this Apache
base
class to add additional require items to Service[''apache2''].

I could pass the dependency list to the class, like so:

class apache2($require) {
	service { ''apache2'':
		require => $require,
	}
}
class { ''apache2'':
	require => [Package[''foo''],
Package[''bar'']],
}

but this requires apache2 consumers to pass the entire dependency list; the
apache2 base class can''t inject its own dependencies transparently.
I''d like
the passed dependencies to be *in addition to* any dependencies the apache2
base class demands.

Is there a sane way to do this?

john
-- 
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On Thu, Sep 22, 2011 at 09:53:46AM -0400, John Morrissey
wrote:
> I''m using an Apache 2 base class based on
>
http://projects.puppetlabs.com/projects/1/wiki/Debian_Apache2_Recipe_Patterns.
> 
> I''d like to pass additional dependencies to the class and/or the
definitions
> it contains. For example, I''d like to allow classes using this
Apache base
> class to add additional require items to
Service[''apache2''].
> 
> I could pass the dependency list to the class, like so:
> 
> class apache2($require) {
> 	service { ''apache2'':
> 		require => $require,
> 	}
> }
> class { ''apache2'':
> 	require => [Package[''foo''],
Package[''bar'']],
> }
> 
> but this requires apache2 consumers to pass the entire dependency list; the
> apache2 base class can''t inject its own dependencies
transparently. I''d like
> the passed dependencies to be *in addition to* any dependencies the apache2
> base class demands.
> 
> Is there a sane way to do this?
I *believe* this will work:

class apache2($extra_requires) {
	service { ''apache2'':
		require => [Service[''foo''], $extra_requires],
	}
}
class { ''apache2'':
	extra_requires => [Package[''foo''],
Package[''bar'']],
}

But I have not tested it.

-Robin

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On Sep 22, 12:54 pm, Robin Lee Powell <rlpow...@digitalkingdom.org>
wrote:
> On Thu, Sep 22, 2011 at 09:53:46AM -0400, John Morrissey wrote:
> > I''m using an Apache 2 base class based on
>
>http://projects.puppetlabs.com/projects/1/wiki/Debian_Apache2_Recipe_....
>
> > I''d like to pass additional dependencies to the class and/or
the definitions
> > it contains. For example, I''d like to allow classes using
this Apache base
> > class to add additional require items to
Service[''apache2''].
>
> > I could pass the dependency list to the class, like so:
>
> > class apache2($require) {
> >    service { ''apache2'':
> >            require => $require,
> >    }
> > }
> > class { ''apache2'':
> >    require => [Package[''foo''],
Package[''bar'']],
> > }
>
> > but this requires apache2 consumers to pass the entire dependency
list; the
> > apache2 base class can''t inject its own dependencies
transparently. I''d like
> > the passed dependencies to be *in addition to* any dependencies the
apache2
> > base class demands.
>
> > Is there a sane way to do this?
>
> I *believe* this will work:
>
> class apache2($extra_requires) {
>         service { ''apache2'':
>                 require => [Service[''foo''],
$extra_requires],
>         }}
>
> class { ''apache2'':
>         extra_requires => [Package[''foo''],
Package[''bar'']],
>
> }
>
> But I have not tested it.

I do not know whether that works, but I would not personally feel
comfortable assuming that it would continue to work from one version
of Puppet to another.

I think this is rather a quirky question in the first place.
Generally one wants to write classes that are fairly self-contained,
and modules that are as much as possible self-contained.  Among other
things, that implies that classes ought to know their own requirements
rather than having to be told them.

A better solution than passing dependencies into a class might be
class-level dependencies.  For example, if you have a Foo resource
that must be applied before all of the resources of class apache2,
then declare the dependency from that side via the "before"
metaparameter:

foo { "my_foo":
  # various properties...

  before => Class[''apache2'']
  # note: that class should be in a module, and
  # referred to by its fully-qualified name
}

Alternatively, if all the resources in Class[''foo_class'']
should be
applied before any of those in Class[''apache2''], then you can
describe
that to Puppet by putting

  Class[''foo_class''] -> Class[''apache2'']

somewhere outside either one.


John

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On Thu, Sep 22, 2011 at 01:11:28PM -0700, jcbollinger
wrote:
> On Sep 22, 12:54 pm, Robin Lee Powell <rlpow...@digitalkingdom.org>
> wrote:
> > On Thu, Sep 22, 2011 at 09:53:46AM -0400, John Morrissey wrote:
> > > I''m using an Apache 2 base class based on
> >
>http://projects.puppetlabs.com/projects/1/wiki/Debian_Apache2_Recipe_....
> >
> > > I''d like to pass additional dependencies to the class
and/or the
> > > definitions it contains. For example, I''d like to allow
classes using
> > > this Apache base class to add additional require items to
> > > Service[''apache2''].
[snip]
> > > but this requires apache2 consumers to pass the entire dependency
list; the
> > > apache2 base class can''t inject its own dependencies
transparently. I''d like
> > > the passed dependencies to be *in addition to* any dependencies
the apache2
> > > base class demands.
> >
> > I *believe* this will work:
> >
> > class apache2($extra_requires) {
> >         service { ''apache2'':
> >                 require => [Service[''foo''],
$extra_requires],
> >         }}
> >
> > class { ''apache2'':
> >         extra_requires => [Package[''foo''],
Package[''bar'']],
> >
> > }
> >
> > But I have not tested it.
> 
> I do not know whether that works, but I would not personally feel
> comfortable assuming that it would continue to work from one version
> of Puppet to another.
nod, the semantics that implies sketches me out a little bit.
> I think this is rather a quirky question in the first place.
> Generally one wants to write classes that are fairly self-contained,
> and modules that are as much as possible self-contained.  Among other
> things, that implies that classes ought to know their own requirements
> rather than having to be told them.
The base class is self contained, but the depending class has resources that
modify the base class'' behavior in such a way that I''d prefer
that those
resources be in place before the service resource is processed. I''m
probably
nit picking in this case, though.
> A better solution than passing dependencies into a class might be
> class-level dependencies.  For example, if you have a Foo resource
> that must be applied before all of the resources of class apache2,
> then declare the dependency from that side via the "before"
> metaparameter:
> 
> foo { "my_foo":
>   # various properties...
> 
>   before => Class[''apache2'']
>   # note: that class should be in a module, and
>   # referred to by its fully-qualified name
> }
ach, I always forget about ''before''. That''ll work
just fine. Thanks.

john
-- 
John Morrissey          _o            /\         ----  __o
jwm@horde.net        _-< \_          /  \       ----  <  \,
www.horde.net/    __(_)/_(_)________/    \_______(_) /_(_)__

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