[strmpnk]

I can also mirror this general guideline. I've run 250+ node erlang clusters just fine in the past. There were some caveats to how some built-in OTP libraries behaved but they were easy to replace or workaround in the past.

That was many years ago as well. The distributed erlang story has improved with more recent releases (better performance on remote monitors for example) which might push the number a little higher than 300 if you are careful. Keep in mind the default style of clustering is fully connected so there is some danger in managing that many network connections (quadratically scaling for each node added) during network partitions which can be a problem if you're not tuning things like TCP's TIME_WAIT for local networking conditions.

Even better, these days there are great libraries like partisan (https://github.com/lasp-lang/partisan) which can scale to much larger cluster sizes and can be dropped in for most distributed erlang uses cases w/o much effort.