Server Sent Events Apache configuration

Question

I'm running a web application using server-sent events (eventsource). I've been working to properly set up the apache and PHP configuration files so that the program will accommodate all of my users and not timeout. I've already set the timeout to an appropriate amount of time in both PHP and apache, but I'm worried about the Server limit, Max Clients, and Max Requests Per Child. I need to connect around 500 users to the php file that runs the eventsource and run a PHP script every time a message is sent to the server. The eventsource file seems to take up about a 1/4 MB of ram and a negligible amount of processing power. Can someone explain what these limits do, and advise me on how best to set them?

Answer 1

Each SSE connection will use a dedicated PHP process, so counts as one of the Apache processes. (Each will also be using a socket and a local port.)

500 simultaneous clients is a lot, even more so if they all use PHP, and you are going to need a lot of memory on your server. But, if you have enough memory, set both MaxClients and ServerLimit to 500. (I'd suggest starting with 50 or 100, run some stress tests, and keep increasing those limits and repeating until you see your server starting to swap.)

For stress-testing SSE, I've found SlimerJS to be the best choice. (The WebKit in PhantomJS (as of 1.9.x) is too old to support SSE.) Selenium would do the job too. Make sure to keep clients and server on different machines, as 100+ clients will also use a lot of memory and load.