First of all, a big shout out to les hommes et femmes at, who today have taught me an important lesson.

At about 9:30 today, they posted a list of 50 things to do with your Raspberry Pi, which included the Raspberry Tank. At about 9:40, my web server melted. This is the disk I/O graph:

Sparrowhawk Disk I/O Graph

Somewhere around five Apache instances per second were being spawned, all of which seemed to be waiting for each others’ I/O operations, and combined together managed to slow everything else to a crawl. It took twenty minutes to successfully ssh into the server and stop Apache. In that whole time, I think about five visitors might have actually have seen a properly-formed web page.

From that point, it was a dainty command-line dance to get enough of WordPress up and running that I could set up a page caching plugin, but not so much of it that visitors could actually request pages themselves.

At around 1pm, I finally managed to get back up and running again – and the floodgates opened.

Sparrowhawk IPv4 I/O Graph

So, today I learned two important lessons about running your own web server:

  1. If you are going to do something cool with a Raspberry Pi and post about it on your blog, CACHE THE PAGES.

  2. It’s a great idea for your web server to send out e-mail alerts when it is dying. It’s a less great idea to host your e-mail system on the same machine.

Thanks, crazy French blog.