define apache2::module($ensure = present) {
  case $ensure {
    present: {
      exec { "Enable Apache module $name":
        command => "/usr/sbin/a2enmod $name",
       }
     }
     absent: {
       exec { "Disable Apache module $name":
         command => "/usr/sbin/a2dismod $name",
       }
     }
     default: {
       fail "Invalid 'ensure' value '$ensure' for apache2::module"
     }
   }
}

# Fails with:
# err: //Apache2::Module[php5]/Exec[Enable Apache module php5]/returns: change from notrun to 0 failed:
apache2::module { "php5": }

# Works:
# notice: //Exec[global scope: Enable Apache module php5]/returns: executed successfully
exec { "global scope: Enable Apache module php5":
  command => "/usr/sbin/a2enmod php5",
}