Michael Morgan

Quite recently I decided to downgrade one of my EC2 instances from a small instance to a micro instance. On this I have about 20 sites running, the majority of which are WordPress with a few other basic web apps and some static HTML sites.

After reading around the general impression I got was that this was a bad idea. Considering the traffic these sites get (several thousand uniques and tens of thousands of visits, daily) I was a bit concerned whether or not a micro EC2 instance could handle this load.

So far, so good. I’ve been keeping a close eye on CPU usage levels as well as memory usage and although it is quite high it is handling it just fine. CPU usage quite regularly spikes to above 50% for short periods of time but the sites always remain responsive and quite snappy. Whilst monitoring the CPU I have seen usage go sky high at peak times at which point the main feature of a micro instance kicks in and you get a performance boost to handle the load.

After a few seconds though CPU steal kicks in taking around 97% of the CPU away. This means for a short period of time the sites become quite slow (less than half a minute I’d say). Considering this happens only once or twice a day (if that) I’m really not worried about it.

Micro instances are much cheaper than small instances and since I’m running non critical sites it really doesn’t matter if the sites slow down a bit for one or two minutes each day. So, if you’re looking to get started on EC2 ask yourself, do you really need a small, medium or large instance? I’m not saying you should put everything onto a micro instance, but I do suggest that you experiment a little first and test the limits. You may be surprised to find that the smaller instances can handle what you need just fine.