while reviewing a change I noticed a comment from @Joe pointing out that lookups for the cluster hiera value need to pass the global $::cluster variable as a default. The use of a global value instead of a hiera default seemed odd to me and the fact that both the global value and the hiera key are named the same seemed a bit confusing.
Looking at the code it seems that we could get rid of the global cluster variable if we simply add a default to labs.yaml and comon.yaml, although i suspect I'm missing some historical context :). Or possibly this was needed before the hiera search order was changed