Re: [Puppet Users] prep for 2.8: default values and overrides

Justin Lambert
2011-08-04T04:03:58Z

Thanks for these - this is very helpful.

On Tue, Aug 2, 2011 at 1:26 AM, vagn scott <vagnscott@gmail.com> wrote:

> **
> prep for 2.8: default values and overrides
>
> I was very happy, some months ago,
> when I worked out how to separate
> configuration from code in puppet.
>
> The scheme even allowed for specialization.
>
> The style was something like this:
>
> cat 04_default.pp
> #! /usr/bin/puppet apply
>
> node default {
>
>         class myfoo1 inherits foo::default {
>                 $foo_param1 = "something else"          # call 1
> specialization
>                 $foo_param3 = "dull and dreary"         # change
the
> default
>                 foo { "call 1": }
>         }
>         include myfoo1
>
>         class myfoo2 inherits foo::default {
>                 $foo_param2 = "anything else"           # call 2
> specialization
>                 $foo_param3 = "dull and dreary"         # change
the
> default again!
>                 foo { "call 2": }
>         }
>         include myfoo2
>
>
> }
>
> class foo::default {
>         $foo_param1 = "something"
>         $foo_param2 = "anything"
>         $foo_param3 = "dull"
>         $foo_param4 = "duller"
> }
>
> define foo() {
>         notice("foo_param1 = ${foo_param1}")
>         notice("foo_param2 = ${foo_param2}")
>         notice("foo_param3 = ${foo_param3}")
>         notice("foo_param4 = ${foo_param4}")
> }
>
> and the output with 2.6.2:
>
>  ./04_default.pp
> notice: Scope(Foo[call 1]): foo_param1 = something else
> notice: Scope(Foo[call 1]): foo_param2 = anything
> notice: Scope(Foo[call 1]): foo_param3 = dull and dreary
> notice: Scope(Foo[call 1]): foo_param4 = duller
> notice: Scope(Foo[call 2]): foo_param1 = something
> notice: Scope(Foo[call 2]): foo_param2 = anything else
> notice: Scope(Foo[call 2]): foo_param3 = dull and dreary
> notice: Scope(Foo[call 2]): foo_param4 = duller
>
>
> But, with 2.7.2rc2  it doesn''t work.
>
>  ./04_default.pp
> Could not parse for environment production: Classes, definitions,
>         and nodes may only appear at toplevel or inside other classes
>         at /u0/home/vagn/puppet-nika/patterns/04_default.pp:5 on node
>         nika.agawamtech.com
>
> Even if I moved the classes out of the node the
> scheme would still fail in 2.8 and later because it
> relies on dynamic scoping.
>
> The following works in both 2.6.2 and 2.7.2.
> It is both a shorter and a cleaner
> expression of the idea.
>
> cat 05_default.pp
> #! /usr/bin/puppet apply
>
> node default {
>
>         class { "foo::default": foo_param3 => "dull and
dreary", }
>         foo { "call 1": foo_param1 => "something
else", }
>         foo { "call 2": foo_param2 => "anything
else", }
>
> }
>
> class foo::default (
>         $foo_param3 = "dull",
>         $foo_param4 = "duller"
> ) {
>         # conditionals and composites would go here ...
> }
>
> define foo(
>         $foo_param1 = "something",
>         $foo_param2 = "anything"
> ) {
>         notice("foo_param1 = ${foo_param1}")
>         notice("foo_param2 = ${foo_param2}")
>         notice("foo_param3 = ${foo::default::foo_param3}")
>         notice("foo_param4 = ${foo::default::foo_param4}")
> }
>
> Note that foo::default MUST be instantiated for there to be
> any values for foo() to reference.  Even if no overrides
> are provided you have to explicitly put
>
>         class { "foo::default": } # required
>
> somewhere in your manifests.
>
> Three observations
>     - most of the work is done in the argument lists
>     - arguments can have defaults
>     - we only have to express the specializations
>
> As always, comments and corrections welcome.
>
> --
> vagn
>
>
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