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I am new to casperjs and planning to use it to accurately simulate anywhere from a few dozen to low hundreds of concurrent sessions accessing a private server on a private network. Unlike typical HTTP load generators (Apache bench, httperf, ...), my purpose is to be able to control each session programmatically (increase delay between requests, have 'smarts' built into each script) and have each session have distinct source IP addresses.

My current thinking is to use OpenVZ containers (openvz.org) to create each 'virtual' client running casperjs (minimal functionality I need is following elements on the UI and taking screenshots). Would love to hear of anyone who has done something similar.

The crux of my question is: what would the 'slimmest' environment for running casperjs be? I'd like to strip down the OS as much as possible to be able to scale multiple clients. Specifically:

  • any recommended low-footprint UNIX/Linux distributions for CasperJS?
  • any specific recommendations on stripping down mainstream (CentOS, Debian, ...) distributions?

Thank you all in advance. I look forward to hearing your input on this specific question or similar experiences/tools for what I'm trying to achieve...

Fernando

Fernando Montenegro
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CasperJS is headless, e.g. it doesn't need X running to function. Any bare bones Linux distribution will do you well.

any recommended low-footprint UNIX/Linux distributions for CasperJS?

Arch is very lightweight and has an easy to follow Beginners Guide. Arch's AUR has a package for CasperJS that's pretty straightforward to setup as well. Just make sure to grab the required base-devel package (pacman -S base-devel) before installing from the AUR as it's needed for the Arch Build System.

any specific recommendations on stripping down mainstream (CentOS, Debian, ...) distributions?

Not so much stripping down, but CrunchBang is based off of the latest Debian release. It may be worth taking a look at. It would be much less of a hassle to setup than Arch, and uses the same APT package manager as Debian / Ubuntu. It installs with the lightweight OpenBox window manager, but you can remove this and X all together if you'd like.

With that said, even a lightweight Linux environment won't help much with the amount of memory each CasperJS instance will use. You could probably pull off a few dozen depending on the amount of memory available, but a few hundred may not be feasible. It all depends on how much memory each website uses. Casperjs comes with some configuration options that may help reduce memory (e.g. don't load images, plugins, etc), but that may defeat the purpose of your tests.

The best advice I can give is to try it out for yourself. Write a simple script that will open the pages you are going to use and pass a callback to CasperJS's run() function to keep it alive (e.g. don't exit from Casper). It can be as simple as:

casper.start('http://example.com/site1', function () {});
casper.thenOpen('http://example.com/site2', function () {});
casper.run(function() { 
    // wait 60 seconds before exit . . . or remove to never exit
    setTimeout(function() { casper.exit(); }, 60000); 
}

Spin up multiple instances, and watch your total memory usage. You can use the cli tools top, or use this alias that totals the amount of memory usage for the current user.

alias memu="ps -u $(whoami) -o pid,rss,command | awk '{print \$0}{sum+=\$2} END {print \"Total\", sum/1024, \"MB\"}'"

From this you should be able to see roughly how much memory each instance takes, and how many you can run at once on one machine.

Jay
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