Accessibility is the most critical measure of your Web site's performance. If customers can't access your site, they can't shop; and if they can't shop, they can't buy. More important, your business could gain a bad reputation among your customers, which translates into negative word of mouth and even worse, if you're highly visible, negative press. So no matter what else you monitor, you want to monitor downtime continuously.
Understand How Downtime Is Measured Measuring whether your site is "up" or "down" seems like it would be pretty easy: Either it's available or it's not. However, effective monitoring for downtime is a bit more complicated. For example, if you can't view your site from a particular PC, how do you know your browser is not causing the problem? Since a variety of factors can all produce the same disastrous end result - downtime - you'll want to monitor accessibility from several different angles.
Troubleshoot Downtime Issues Whether you detect downtime on your own or are alerted to it with the help of a monitoring service, you must take immediate action to correct the problem. You'll be better prepared to do so if you understand the possible causes of your site crash. Going through the process of troubleshooting downtime can be frustrating and sometimes costly, but look on the bright side: After going through this process once, you'll be better able to cope with - and ideally prevent - such crises in the future.