On Mon, Feb 14, 2011 at 6:49 AM, Nigel Kersten <ni...@puppetlabs.com> wrote:
> On Sun, Feb 13, 2011 at 9:59 PM, Dan Bode <d...@puppetlabs.com> wrote:
>
>>
>> We have only been teaching <| |> in the puppetmaster training as a way to
>> realize virtual resources. We do not teach that it is possible to override
>> attributes with this syntax as well: <| |> {} (at least in part b/c the
>> implications/non-determinism terrify me) , and do not teach that it actually
>> effects all resources.
>>
>
> Why is using collections to override attributes non-deterministic compared
> to class inheritance doing the same thing?
>
With the below example, the evaluation order of the overrides determines the
final value.
notify { 'foo':
message => 'bar',
}
Notify<| |> {
message => 'bazz'
}
Notify<| |> {
message => 'baz'
}
# try this example and swap the overrides
With class inheritance, any attempt to override the same attribute twice
fails:
class a {
notify { 'foo':
message => 'a',
}
}
class c inherits a {
Notify['foo'] {message => 'c'}
}
class b inherits a {
Notify['foo'] {message => 'b'}
}
include a,c,b
:!puppet apply /tmp/foo2.pp
Parameter 'message' is already set on Notify[foo] by
#<Puppet::Resource::Type:0xb7a430c8> at /tmp/foo2.pp:9; cannot redefine at
/tmp/foo2.pp:12 on node mypuppetmaster.localdomain
The common example from class is something like:
>>
>> class db::users {
>> user { ['alice', 'bob']:
>> ensure => present,
>> gid => 'dbadmin',
>> }
>> }
>>
>> class app::users {
>> user { ['charlie', 'bob']:
>> ensure => present,
>> gid => 'webadmin',
>> }
>> }
>>
>>
>> class app {
>> User<| gid == 'webadmin' |>
>> ...
>> }
>>
>> class db {
>> User<| gid == 'dbadmin' |>
>> ...
>> }
>>
>> so that a machine can safely be a webserver and db server without
>> conflict.
>>
>
>
> Why is this preferred over the realize() function? I consider the realize
> function much simpler to teach and understand for this class of problem.
>
The realize function requires that we have to know all of the names of the
resources that we are realizing. Consider the example where each group of
users has 10 members, the above syntax is way easier to manage than:
realize(User[1], User[2], .... User[10])
>
>
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