How to properly scale nodejs app on heroku using clusters

I noticed a warning in heroku logs lately saying that seemed new to me

web.1: Detected 512 MB available memory, 512 MB limit per process (WEB_MEMORY)

web.1: Recommending WEB_CONCURRENCY=1

I did some research and found this cluster article, which is the "default" way to use clusters in nodejs, but it totally contradicts with a newly updated article that contains this new WEB_CONCURRENCY environment variable and with a different size suggestion for each dyno (which is much smaller, btw)