heroku/heroku-buildpack-python — pull request #20 by yaniv-aknin (2012-01-01 06:32:17+00:00)
Title: Create a HEROKU_RELEASE_ID file with a UUID4

I humbly think Heroku should do this by default in every buildpack; the
choice of UUID4 was borderline arbitrary, any unique ID will be fine.

Quoting http://www.12factor.net/build-release-run
"Every release should always have a unique release ID, such as a
timestamp of the release (such as 2011-04-06-20:32:17) or an
incrementing number (such as v100). Releases are an append-only ledger
and a release cannot be mutated once it is created. Any change must
create a new release."