It's mostly RAM allocated per client. E.g. Postgres is very much limited by this fact in supporting massive numbers of clients. Hence pgbouncer and other kinds of connection pooling which allow a Postgres server to serve many more clients than it has RAM to allow connecting.
If your Node app spends vety little RAM per client, it can indeed service a great many of them.
A PHP script that does little more than checking credentials and invoking sendfile() could be adequate for the case of serving small files described in the article.
If your Node app spends vety little RAM per client, it can indeed service a great many of them.
A PHP script that does little more than checking credentials and invoking sendfile() could be adequate for the case of serving small files described in the article.