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(I know I'm late in responding; I'm a couple of months behind in reading
the mailing-list, and still have 2000 unread. I have read this entire
thread, though.)
On 2012-01-19 18:18, Nigel Kersten wrote:
> I'm looking for strong opinions on whether we should or shouldn't deprecate
> the defined() function for Telly, the next major Puppet release this year.
>
> jcbollinger put it quite well in another thread:
>
> "Use of the "defined" function introduces a parse-order dependency, and the
> additional work you need to do to ensure that that dependency is always
> fulfilled overcomes any simplicity advantage that might otherwise exist."
- -1 until there is some other, usable, way of realizing the good things
you can achieve with defined().
My use case for defined() is in definitions that wants to make sure
a package it needs is installed, and where that package varies between
instances of the definitions. For example, I have a definition named
nrpe::check, which configures a Nagios NRPE check. It wants to make
sure the appropriate nagios-plugins-PLUGIN is installed, so it does
(simplified, and just retaining the code dealing with the package):
define nrpe::check($plugin='', $checker='', $args=[], $prefixcmd=[])
{
$pluginpkg = $plugin ? {
'' => "nagios-plugins-${name}",
0 => '',
default => $plugin,
}
if $pluginpkg != '' and ! defined(Package[$pluginpkg]) {
package {
$pluginpkg: ensure => installed,
}
}
}
A user would do things like:
nrpe::check { 'load': args => [ '-w20,10,8', '-c30,18,10' ]; }
and the "nagios-plugins-load" package will automatically be installed.
This becomes interresting when you have:
nrpe::check { 'test_foo': args => ['foo'], plugin =>
'nagios-plugins-ourtest'; }
and
nrpe::check { 'test_bar': args => ['bar'], plugin =>
'nagios-plugins-ourtest'; }
both using the same plugin, but with different parameters, in different
parts of the manifest for the node. The cincher here is that there are
several dozens of Nagios plugin packages available (EPEL has 63, many
organizations probably have several of their own, and so on).
It would be possible to instead have the nrpe::check definition do
include "nagios_plugin_package::${plugin}"
and force the user to define a class for each plugin they use (and I
could of course "pre-seed" by writing 63 of those myself in my nrpe
module). But it becomes much easier on the users of the nrpe module
if they don't need to do so.
This use of defined() is safe, since there is really only a single
declaration of each Package['nagios-plugins-PLUGIN'] resource.
I'm not fond of defined(), as it is easy to get wrong, but it is also
quite useful in some cases. It would be a shame to deprecate a useful
feature before there is a workable way to achieve the same end results
in place.
/Bellman
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