Super easy and have not had an issue with it in over 10 years of using it. There is an example here on how to do it with docker image. https://mailsnag.com/blog/optimized-ruby-dockerfile/.
OOC, why isn't this part a ruby default? Isn't it always better to be more memory efficient. (I'm trying to understand what the trade offs are, if any)
EDIT: well, exactly 6 minutes later, I'm done. I followed these instructions: https://elements.heroku.com/buildpacks/gaffneyc/heroku-build...
The app seems to work like usual, I'll just have to wait and see what happens to memory use.
I will reply here in 12 hours with a screen shot showing the results (before/after memory use), whatever they may be.
Also, for reference, here's the metrics for the past 24 hours (LOTS of memory problems): https://imgur.com/a/M8IHd5z
It looks like memory usage did indeed go down, and critical errors fell by about 84%.