Style Guide 11.9

init.pp

# = motd class
#
# A Hierarchy of Class Param Value => Node Param Value => Module Default Value
#
# WITHOUT _real and UNSET ugliness!  Hooray!
# ... but WITH inherits!  Boo..?
#
# The class param value part of the hierarchy happens here since this is a parameterized class.
# The node param value and module default part of the hierarchy happens in params class
# we're inheriting from.
#
class motd (
  $banner_content = $::motd::params::banner_content,
  $banner_source  = $::motd::params::banner_source,
) inherits motd::params {
  file { '/etc/motd':
    owner   => 0,
    group   => 0,
    mode    => 0644,
    content => $banner_content,
    source  => $banner_source,
  }
}

params.pp

class motd::params {
  # The Node param value and Module default part of the hierarchy happens here
  # The undef key is the module default value and
  # the default key is the node param value.  Neither of these are used if the class parameter value
  # is specified.
  $banner_content = $::motd_banner_content ?
    undef   => 'THUG LIFE (Whatever the heck that means...  This is the module default value.)',
    default => $::motd_banner_content,
  }
  $banner_source = $::motd_banner_source ?
    undef => undef,
    default => $::motd_banner_source,
  }
  # We should probably make sure the user doesn't specify both...  But we don't because we're lazy.
}

site.pp

# Use cases

# Simple case (puppet apply -e 'include motd')
include motd

# Simple case with customization
# puppet apply -e 'class { motd: banner_content => "Puppet: $puppetversion" }'

# Puppet Enterprise Console
node default {
  $motd_banner_content = "This variable could have been set in the GUI"
  # The GUI could have included the class for us as well!
  include motd
}

# Use our own file _without_ Puppet Enterprise
node default {
  class { motd:
    banner_source => "puppet:///sitefiles/motd.erb",
    banner_content => undef,
  }
}

# Use our own file WITH Puppet Enterprise Console
# Both the class and the variables can be set using the GUI
node default {
  $motd_banner_content => undef
  $motd_banner_source => "puppet:///sitefiles/motd.erb"
  include motd
}

# EOF

There's one bug where you still have no way to differentiate between $motd_banner_content as a node parameter being explicitly set to undef or being implicitly not set.

I think we could work around this in motd::params by just always setting $banner_content to undef is $banner_source is defined by the user somewhere.