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Minimal Apache/Rails configuration on small virtual server

As I’ve mentioned before I’m running a couple of WordPress blogs and a Rails application on Slicehost, using the smallest slice size of 256 MB RAM. Apart from Rails, this is a typical LAMP setup with Ubuntu Hardy Heron, Apache2-prefork, MySQL 5.x, PHP5. It took a little while for me to find a robust Apache and Rails configuration, though. The out of the box Apache2 config would periodically eat up all the swap space and die. So my hope here is to save others some newbie-sysadmin headaches.

Apache2. Apache2 prefork is configured to keep a certain number of processes running to respond to HTTP requests that come in. These processes are reused across a number of requests and thus tend to grow over time in their memory consumption to reach the largest amount of RAM demanded by any page served. When using mod_php, the RAM consumption is related to PHP application resources, in this case WordPress. I found that my Apache processes generally were in the 20m range for resident memory size (the RSS column in the ‘top’ display). With the out-of-box Apache2 configuration allowing as many as 15-20 processes, that meant that any large batch of concurrent requests (such as those originating from a search bot) would totally nail my machine. So the most important change I wound up making was to reduce the number of processes:

<IfModule mpm_prefork_module>
    StartServers          3
    MinSpareServers       3
    MaxSpareServers       3
    ServerLimit          10
    MaxClients           10
    MaxRequestsPerChild   1000
</IfModule>

This generally causes me to see around 5-6 processes running, with the possibility of as many as 10.

A number of folks have suggested I run nginx or lighttpd, which I’m sure would be a great idea, but I was strapped for time and in a mood to stick with things that have lots of online recipes and that I already somewhat understood.

Rails. Various approaches are available here as well. At first I was running the mod_passenger module, but I found this gave me a few 30m processes as opposed to the single 50m process I could get by running a single mongrel. So now I’m running a single mongrel and it’s working fine.

MySQL. Haven’t tuned this much yet, but I’m not seeing any problems.

WordPress. Caching is enabled on the advice of a number of people that this will decrease MySQL resource consumption.

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