Editing hosts.allow with augeas

allow.pp

define hosts::allow($process, $ensure=present) {
  if $ensure == 'present' {
    augeas { "Add ${name} to ${process} hosts.allow":
      context => '/files/etc/hosts.allow',
      changes => "set *[process='${process}']/client[last()+1] ${name}",
      onlyif  => "match *[process='${process}']/client[.='${name}'] size == 0",
    }
  } else {
    # exercise for the reader
  }
}

site.pp

hosts::allow { ['10.128.100.12', '10.128.100.14']:
  process => 'nrpe',
}