Hmm. That is odd. There have been some strange issues with ram requirements reported lately. You might just try again a few times. Some reports say that it’s failing intermittently.
Edit: sorry. 127 is ram. 128 is unknown.
You’re doing a standard install from scratch running discourse-setup? (you say so in OP)
Are you behind some kind of firewall that might keep the server from accessing github and other repositories?