You get a call in the middle of the night. "Our website isn't working," your boss yells. In seconds, you are wide awake and trying to remember "what exactly did we change yesterday?"—this is a very natural reaction for every system administrator on this planet.
Have you ever been in such a situation? This is a stress test for each young sysadmin, and we hope you have had this earlier in your career rather than later because it is a teaching experience. Fortunately, websites usually malfunction when they are mostly loaded and this happens during the late morning or early evening hours—if you are lucky to live in roughly the same time zone as your target audience. For example, this is a traffic graph for a big website in Russia, which is a country very centered around its two capitals, and those cities are both in UTC+03 time zone as of 2016:
As you can see, the real traffic comes in the morning, has a peak in the evening, and falls sharply as people...