It is vital during the execution phase to monitor all aspects of the website. This includes measuring and monitoring the CPU usage and performance aspects of the various components of the website, i.e. not just the webserver, but the database and other parts aswell (such as firewalls, load balancing tools etc.)

For example, one e-tailer, whose site fell over (apparently due to a high load), when analysing the performance bottlenecks on their site discovered that the webserver had in fact only been operating at 50% of capacity. Further investigation revealed that the credit card authorisation engine was the cause of failure - it was not responding quick enough for the website, which then fellover when it was waiting for too many responses from the authorisation engine. They resolved this issue by changing the authorisation engine, and amending the website coding so that if there were any issues with authorisation responses in future, the site would not crash.

Similarly, another e-commerce site found that the performance issues that they were experiencing were due to database performance issues, while the webserver CPU usage was only at 25%, the backend db server CPU usage was 86%. Their solution was to upgrade the db server.

Therefore, it is necessary to use (install if necessary) performance monitoring tools to check each aspect of the website architecture during the execution phase.