How to measure RTT to webserver clients?

Question

System administration

Hello
I would like to know what is the average rtt to clients coming to my webserver, to evaluate the efficiency of cdn.
Is there any way to find out how long it takes for clients to receive my packets? It seems that $tcpinfo_rtt ( nginx.org/ru/docs/http/ngx_http_core_module.html#v...
) could help with this , but the numbers that it gives are very different from reality (150ms against real 2-3 for example). How does it actually work and can this value be trusted? Is there any other way to get this number?

Answer 1

150 ms is an adequate time, especially if you divide it by 2. Personally, I have not seen a single network that works like this. I have 2-8 ms ping to wi-fi router. Those. 1 hop. So welcome to the real world, where RTT can be seconds, because it all depends on the transmission medium. For example, if you are transferring data through a low-speed connection, then it can lag quite a lot. An excellent example of this is GPRS in conditions of unstable reception.

Answer 2

In general, I had an old centos with route cache, I took a number from it with rtt and drew it.
The picture is more than sad - rtt is less than 100ms only for 30% of visitors and almost does not change during the day.
i.imgur.com/iElWinP.png