5. Load Balancing and the Utter Confusion Surrounding It
We discussed the differences between load balancing and high availability in Chapter 4, "High Availability. HA! No Downtime?!," so we will pursue that topic by seeking a better understanding of load balancing.
First, let's reflect on the term load balancing. Although it is obvious what it meansto balance a loadit is often misunderstood to mean balance the system load. System load is defined as the average length of the run queue (processes in a runnable state waiting for the system processor) over the last 1 minute, 5 minutes, and 15 minutes; typically updated on 5-second intervals.
When you type uptime on your Unix or Linux system, you should see something like what I see on one of our production web servers:
9:38pm up 292 days, 23:35, 0 users, load average: 0.94, 0.75, 0.70
The numbers seen at the end are the 1-, 5-, and 15-minute load averages, respectively. So, what is wrong with thinking of load balancing as an attempt to even the load average of the machines in a cluster? In short, everything.