bosh faster prepare deployment diff

bosh-faster-prepare-diff.txt

does the unrendered template have a fingerprint?
can i build list of template's used properties? probably with ruby magic
can also warn about unused properties here as a bonus side-effect feature

inputs to final template
    template itself (fingerprint unrendered)
    job property values from manifest directly (ordered & hashed?)
    credhub variables (version ids) 

compare properties from manifest that would be used in the template
    not entirely sure how yet. unless we have digest(template + manifest var vals) stored vs digest(template)
    values are technically stored in old manifest (!) grab there
    can also detect any that have been added (and required, prevent job failure) or gone away
compare target template fingerprint with current
    if there is a change
    then defer a renrender
all variables in template that will be interpolated
    compare current version with version returned in get current from credhub
        if versions are different
        then there will be potentially a different value so defer rerender
otherwise, nothing has changed
rerender prior to sending templates

also if converge or overwrite variables update_mode is set to !nooverwrite check first to short circuit hard. don't know relationship of variable value to remainder of templates so must render all.

diff can explain further
  what releases
  what templates
  variables
  leads to updating the whole vm