How many users can an Amazon EC2 instance serve?

Question

The use will be to serve dynamic content from data on S3. You can make up any definition of "normal" you think is normal.

What about small, medium, and large instances?

Ok. People want some data to work with, so here:

The webservice is about 100kb at start, and uses AJAX, so it doesnt have to reload the whole page much, if at all. When it loads the page, it will send between 20 - 30 requests to the database (S3) to get small chunks of text (like comments). The average user will stay on the page for 10 min, translating to about 100kb at offset, and about 400kb more through requests. Assume that hit volume is the same at night and day.

Answer 1

Depends on with what and how you're serving the content, not to mention how often those users will be accessing it, the size and type of the content, etc. There's essentially not one bit of information you've provided that allows us to answer your question in any sort of meaningful way.

Answer 2

One can argue that properly designed, it doesn't matter how many users an instance can support. Ideally, when your instance is saturated, you fire up a new instance to manage the traffic.

Obviously, this grossly complicates the deployment and design.

But beyond that, an EC2 instance a low end Linux box, effectively (depending on which model you choose).

Let's rephrase the question, how many users do you want to support?

Answer 3

As others have said, this might require testing under your exact conditions. Fortunately, if you're willing to go as far as setting up a test version of your server setup, you can spawn instances that simulate users. Create a bunch of these test instances, and run Apache's ab benchmarking tool on them, directing them at your test site. If the instances are within the same availability zone as your test site, you won't be charged for bandwidth, just by the hour for the running instances. Run a test for under an hour, shutting down the test instances afterward, and it will cost you very little to organize this stress test.

As one data point, running the Apache ab tool locally on my small instance, which is serving up a database-heavy Drupal site, it reported the ability of the server to handle 45-60 requests per second. I'm assuming that ab is a reasonable tool for benchmarking, and I might be wrong there, but this is what I'm seeing.

As a suggestion, not knowing too much about your particular case, I'd move your database to an Elastic Block Store (EBS) volume. S3 is not really intended to host databases, and the latency it has might kill your performance. EBS volumes can easily be snapshotted to S3 for backup, if that's what you're worried about.