I saw this thread and have a similar issue with my app. I’ve found the issue isn’t how many concurrent connections can one small Meteor container handle (BTW it’s a lot - like 400+ before I stopped testing), what you’ll run into before that is how many simultaneous logins (bursts of users) the server can handle before it slows to a crawl. And the answer is not much… like less than fifty for a small container.
Concurrent users just clicking around your app aren’t intensive on the server. Users downloading your app payload for the first time, all at the same time is highly intensive on your server.
I wrote a very detailed thread about it here - hope it helps: