There are some important differences here between NodeJS and Ruby. NodeJS child processes are completely independent and created with spawn. https://github.com/nodejs/node-v0.x-archive/issues/2334

CRuby forks using fork() and Copy-on-Write shares memory from parent to child.

JRuby doesn't have a GIL so you only need a single process. Same with TruffleRuby.

With CRuby, you're much better to run a bigger container with multiple processes than one process per container.

With either NodeJS or CRuby you're still better to run less containers on bigger hosts. Each host has to duplicate the host OS and container infrastructure. Each container of a real production app also duplicates a bunch of stuff despite Docker's best attempts at sharing.