performance - how does one identify why a website is slow? -

I was asked this question once in an interview:

"Suppose you One website where the server is at some remote location One day, some users are calling you at the call / email saying that the site is abominable, why would you identify the site slow? Besides, when you own a website Also checks the browser as a user), the site behaves properly. "

I L can think of one thing I (which went shot down):

• Server Czech log analysis of incoming traffic is probably a DoS attack or exceptionally high traffic. The interviewer told me that the server does not have normal traffic and no DoS.

  I was lost in a way because I never thought of this problem. I have almost no idea how a server / website is working, so if someone can highlight some of the methods then it would be good.

  While googling around, I can find that this article is very technical to me now, but I'm breaking it slowly and understanding it.

  Since you already said that when you check the site the speed is fine, its meaning There is nothing wrong in the server (for at least the pages you have checked) and it can serve the pages at a good pace, at this point you should know that you and your site report The user who is slow is slow, what is the difference. This can be several different things:

  • Is the user using a slow network connection (for example mobile)?
  • Is the user hosted by other websites in the same webhostster? If so, it can indicate a network problem. Usually it can also indicate a processing problem on the webserver, but in that case the site will be slow for you too.
  • If no one answers in the above answer, you can assume that the server and the server themselves are OK. This means that there should be a problem with the user device. Find out which browser / OS uses and try to repeat the problem. If it uses any antivirus or software that can cause problems then it fails to detect it.