Puppet

The puppet parser has number of issues regarding order-of evaluation:

• It does not always ensure that included classes are evaluated before qualified variables referring to them are evaluated. (LanguageTutorial)
• It may evaluate classes before the scope in which they are defined is evaluated.
• the defined() function is “unfortunately dependent on the parse order of the configuration when testing whether a resource is defined.” (FunctionReference)

As far as I understand it, the intent is that puppet is a declarative language, in which order of evaluation should not matter, and it would be nice to have these issues cleared up. Conversely, if puppet continues to be “somewhat order dependant”, stronger mechanisms to provide control over order-of-execution or at least make order-of-execution more predictable are necessary. I believe the former is preferable.

The following example demonstrates the first two of these problems (tested on both 0.24.5 and HEAD):

######################################
# define some classes

class apache {
        apache_setup { "config" : }
}

define apache_setup (
        $chroot = true,
        $ssl = false
) {
        # sanity checking, platform-specific defaults
        $_chroot = $chroot
        $_ssl = $ssl

        class apache_config {
                $ssl = $_ssl
                $chroot = $_chroot
                # more variables here
        }
        include apache_config
        # actuall apache setup goes here
}

class trac {
        case $apache_config::chroot {
        true: {
                notice("chroot = true")
                # do something
        }
        default: {
                # do something else
                notice("chroot = ${apache_config::chroot}")
        }
        }
}


######################################
# Now use what we've set up

class apache_ssl inherits apache {
        # override the defaults
        Apache_setup["config"] {
                ssl => true,
                chroot => false
        }
}

include apache_ssl
#include apache_config
include trac

If this example is executed as-is, we recieve the error, it has clearly been included in apache_setup. (issue 1 above)

Class apache_config has not been evaluated so its variables cannot be referenced at /tmp/foo:26 on node 000AE43B1909

If we uncomment the ‘include apache_config’ directive at the bottom of the example to ensure that puppet sees the class as being included, puppet evaluates apache_config before the apache class and apache_setup define; the scope in which apache_config is defined is not evaluated, and the variables it depends on are evaluated as empty strings. (issue 2 above)

notice: Scope(Class[trac]): chroot =