In my application a lot of functions access other company's web API.
DNS resolve is often abnormal in the last month. I think that is not nameserver problem.
I using facebook API by curl in application shows "Could not resolve host", but sometimes work success, 3 times 1 time failed(resolve timeout or waiting more then 1 min).
It's can also show in command line "ping", "mtr", I took a small video to show this issue.
I tried to modify nameserver to 22.214.171.124, 126.96.36.199, 188.8.131.52, 184.108.40.206, or 220.127.116.11, all public nameservers.
I also try to disable the IPv6 nameserver, but the problem still exists.
First, I think that is not my country's network problem, because I tried to ping facebook, google, yahoo....alse have same problem.
Second, this has nothing to do with the operating system, because I have 7 Vultr VPS, I have Ubuntu, CentOS, Windows Server, there all have same problem.