Monitoring Drupal sites
Once your site launches, you may be spending less time checking on it than while you were building it. It may be helpful to use a monitoring service to let you know if your site experiences downtime, so you can promptly check it out and try to resolve the source of the problem. While it’s inconvenient that the options available all require external services and/or software, it also makes sense: some kinds of issues (particularly at the server level) could take down the monitoring system along with the Drupal site if the two share infrastructure.
Nagios is a widely-used open source monitoring application, and there is a Drupal module that integrates with it. (Note: you don’t have to use the Drupal module; you can configure Nagios itself to just check the front page of your site, though you might also want to set it up to check the search results page for a search term that you know will have results, to make sure that dynamic pages are loading.) It needs to be installed somewhere, ideally on a separate server (and in a separate hosting environment) than the sites you’re monitoring. UC Berkeley’s Research IT group uses Nagios to monitor its websites.