How many concurrent users can a web app built in Meteor.js handle? [closed]

UPDATE ClassCraft reports one Meteor server handling 6400 concurrent users. Read more in the Scalability section of my Why Meteor article.

See also the forum post
How Many Simultaneous Users Does the Biggest Current Meteor App Support?

Here's a benchmark not exactly about concurrent users, but rather about setting up subscriptions (arguably a more stressful test).

Arunoda has recently published the results of a test using meteor-down (a load testing tool similar to @alanning's meteor-load-test) and Cluster, a Meteor load balancing tool.

The test was run on the cheapest Digital Ocean servers (512MB RAM, $5/month), and the results were rather impressive:

For all the above scenarios, server response time is less than 8ms.

Essentially one commodity machine can handle 2500 Meteor subscriptions per minute and respond within 8 miliseconds. Horizontal scaling takes less than 5% overhead.

You can read more about the test at Meteor Cluster Performance Test: Impressive Results.

https://github.com/alanning/meteor-load-test

If you mock up the app quickly, it should be fairly straightforward to set up a test for 4000 connections over a 15 minute period. I haven't used it personally but plan to do so once I finish fleshing out my own application.

I think the honest answer is that every case is different, and there are no hard and fast rules that people can give you in terms of how your system will perform under different loads.

Your best bet is to actually build a simple prototype of your system, with one or two functions, and then look to run some performance testing using multiple concurrent users to determine what the limitations are. This should give you a good basis to then iterate on your prototype and work out if/how you can support the number of users you require.