Why do virtual machines slow down on a powerful server?

Question

virtual box

There is a server with stuffing: Intel E3-1270v2, 512GB SSD, 32GB, Windows 7 64bit, 1Gbit. This server has VirtualBox installed, and it has a bunch of identical windows 7 32bit machines. A simple script (python + selenium) runs on each virtual machine, which connects to the same site through a proxy (testing). Now to the point: with 5 running virtual machines, the load on the processor is 10-20%, RAM is occupied by 12 GB out of 32, the network is 3-5 Mbps, and when 6 or more machines are launched, strong lags begin, it feels like there is not enough bandwidth network capabilities, although this is clearly not the case, and there are enough proxies, so it's clearly not about them. Tell me, please, in which direction to dig?

Answer 1

Check the network with iperf. Can't it be that the backend is slowing down?

Answer 2

Why do virtual machines slow down on a powerful server?

Why guess? Measure the load on the server and it will immediately become clear.

with 5 running virtual machines, the load on the processor is 10-20%, RAM is occupied by 12 GB out of 32, the network is 3-5 Mbps, and when 6 or more machines are launched, strong lags begin

Well, there is another disc.

A simple script (python + selenium) runs on each virtual machine, which connects to the same site through a proxy (testing)

And what prevents you from running a hundred of these scripts on one virtual machine? Somehow to fence the whole virtual machine for the sake of one script is too much.

Answer 3

Real Jedi have been using headless browsers for a long time.
Read and stop generating virtual machines for every sneeze.