At our Drupal development company, we know how many benefits this CMS have. However, even Drupal-based sites are not free from errors, which could occur for a host of reasons like hardware troubles. When that happens, you should always know what to do.
First of all try to prevent errors. One way to do it is to use caching, which helps save your hardware resources. You can also increase the memory limit, which is done in the php.ini file. How much you change the limit depends on your server capabilities and on the scale of the site. And finally, consider backing up your server.
When the disaster has struck after all, there are several ways to get to the root of evil. Note down all the crucial information about the failure: when it occurred, which server suffered, when the situation got back to the norm, etc. You can also set up remote log-sharing and instruct your server to send data to the logging tool.
Then, try to reproduce the failure by using a replica of the live environment where the problem originated and executing scripted tests there. And, certainly, start experimenting with possible solutions. You may have fixed the error even without a full understanding of what caused it.
Drupal web development produces great sites. Although performance failures do occur, by knowing what to do in case of trouble, you can quickly get things right again.