linux

In Jauary we migrated a Drupal site that routinely has 40k+ hits per day. We moved the site from servers in the Pacific Northwest to a datacenter in Virginia. As if that wasn't enough, we moved the servers from Apache to Nginx, as well. But what makes this remarkable to me is that we managed to pull this off without so much as a minute of downtime. This blog explains how we did it (and it uses lots of pretty diagrams, too!).

Tuning Nginx ("engine-X") seems to be something of a black art. Today, I looked closely at the tcp_nopush, sendfile, and keepalive_requests settings for pages rendered from PHP as a FastCGI, and memcached content. We discovered that with a little careful tuning, we could shave off as much as 200-400 msec per request.

I have been working on several speed improvements on the Condition Centers at Spine-Health.com. Initially, these pages were taking upwards of 3.5 seconds just to render the HTML. Through a series of optimizations that I will document in another article, we have the conditions page rendering in around 100 msec now.

Before we get going, let me mention a few details of our system:

• We are running CentOS 5.3 (roughly equivalent to RHEL 5.3)
• We are running Nginx 0.6, which is behind the current stable, but is the latest in the Fedora EPEL repositories that we use.
• Since these settings make use of low-level kernel facilities (like TCP_UNCORK), other platforms may differ.

Nagios is a network monitoring tool. I use it to track web servers, mail servers, and whatever else I have running on the LAN and on the Internet.

One common configuration issue is getting the Service Commands menu to work correctly. By default, it is visible in the UI, but disabled on the server backend. And on Debian, not all of the steps to enable it are particularly evident from the docs. Often, one will recieve the cryptic error Could not stat() command file pointing to /var/lib/nagios3/rw/nagios.cmd. This can be fixed without too much fuss.
Nagios Service Commands

Today I needed to run a simple script against thousands of identically named files nested in a huge directory structure. What I needed was a quick way to recurse through all of the directories, ignore all of the files I didn't care about, but run a specified command on any files with a particular name.

While this sounds like the sort of thing that will require a couple dozen lines of shell scripting, it can actually be accomplished on a single line with the command find. find has been around for decades, and can be found on almost any UNIX-like file system. It is a simple to used for searching for files within the UNIX directory hierarchy. Honestly, there's not much more to it. Like all good UNIX tools, it does one thing well.