Is paramater ordering non-deterministic?

[Robert Rothenberg]

I've run into the following issue with parameters that are dependent on each other. Suppose I have the following class:

  class foo(
    $owner,
    $prefix  = "/opt/${owner}",
    $etc_dir = "${prefix}/etc"
   ) {

   file{"${etc_dir}":
    ensure => directory,
    owner  => $owner,
    group   => $owner,
    mode   => 0660,

    ...

 }

The order that the parameters are defined appears to be non-deterministic, so that sometimes $etc_dir is defined before $prefix. Which means that $etc is set to '/etc', and of course, this restricts the permissions on /etc, which breaks the server (including preventing any user, including root, from sudoing!).  Fortunately, this was found while testing manifests on disposable virtual machines. I shudder to think what would have happened if we didn't figure out the cause and deployed this on actual servers.

So, am I correct in assuming that the order of parameter setting is non-deterministic (and so should avoid setting them like above), or is there something else going on?

If parameter order is not deterministic, I do think it should be explicitly documented, with a warning about what can go wrong. (Apologies if I've been daft and missed an existing mention of this somewhere.)

FWIW, I added a note to http://projects.puppetlabs.com/issues/4408 about this issue.

[Henrik Lindberg]

The evaluation order of the parameters is not deterministic as I learned
when implementing validation of references in Geppetto. (BTW, Geppetto
issues warnings/errors when trying to reference potentially
uninitialized variables as in your example).

You need to move the logic computing the resulting defaults inside the
class to be able to use the $owner and $prefix values.

Regards
- henrik

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[Robert Rothenberg]

So will the setting of the values for $owner and $prefix be deterministic, when set inside a class or resource definition?

Also, what if I want to be able to override these with user settings? (That's one of the reasons that they are parameters in the first place.)

[jcbollinger]

On Apr 16, 8:22 am, Robert Rothenberg <rob...@gmail.com> wrote:
> So will the setting of the values for $owner and $prefix be deterministic,
> when set inside a class or resource definition?

Manifest code inside a class or definition is processed in lexical
order.

Note also that some programming languages behave similarly to Puppet,
in that their specifications do not require function arguments to be
evaluated in order. C, for example.

> Also, what if I want to be able to override these with user settings?
> (That's one of the reasons that they are parameters in the first place.)

This is the usual idiom:

class foo(
$owner,
$user_prefix = '',
$user_etc_dir = ''
) {
$prefix = $user_prefix ? { '' => "/opt/${owner}", default =>
$user_prefix }
$etc_dir = $user_etc_dir ? { '' => "${prefix}/etc", default =>
$user_etc_dir }

...
}


John

[Nan Liu]

On Mon, Apr 16, 2012 at 6:22 AM, Robert Rothenberg <rob...@gmail.com> wrote:
> So will the setting of the values for $owner and $prefix be deterministic,
> when set inside a class or resource definition?

Yes. The issue with parameters in class declaration is described in
further details here:
http://projects.puppetlabs.com/issues/9848

> Also, what if I want to be able to override these with user settings?
> (That's one of the reasons that they are parameters in the first place.)

John's example works with the edge case where you actually want to set
a variable to '', you'll see our documentation list 'UNSET' as the
default for this reason:
http://docs.puppetlabs.com/guides/parameterized_classes.html

Thanks,

Nan