Avoid Downtime: What's the point of going through the effort to create a website if it's offline? If a website falls down in a forest, it does make a sound. Unreliable websites hurt your brand.
Keeping Web Hosts Honest
Some web hosts advertise "five nines" availability, meaning your server will remain available 99.999% of the time, which allows for five minutes of downtime per year. Do you have any method of verifying these claims?
Website speed is a major factor in usability. Comparison shopping site Shopzilla reduced latency by five seconds and witnessed a 12% increase in revenue. Google and other search engines now include website speed as a factor in rankings. Many web server monitors include logging and can report on your site's performance over time.
Why You Need External Web Server Monitoring
Many companies use internal tools like Nagios to monitor the status of their public websites. These are a good start, but you need to mimic your customers' experience from a location completely outside your corporate network. Here are a few reasons why.
If you misconfigure external DNS, any server may encounter a problem. However, your internal users and tools would not observe the problem because internal DNS records are often managed separately from external records. If you encounter an unexplained outage, try running an nslookup from an external server that's not on your company's network. You can also use http://www.dnstools.com/. Make sure the external DNS returns the correct IP address for the server.
Custom Network Routes
Companies often set up custom network routes or VPNs to provide special access to the server for developers and content editors. These custom routes will distort the internal experience. Perhaps they direct traffic to one machine within a load balanced environment. Internal tools that use custom network routing will not observe the same results as external users.