How many cpu and memory for Rancher Server to support manage 300 client servers

How many cpu and memory for Rancher Server to support manage 300 client servers.

I deployed a 4cpus, 8G memory Rancher server, and add ten hosts once at a time.
It worked fine when total number of hosts in environment less than 100.
If the total number of hosts is large than 100, Rancher server’s cpu usage will come up to 90% when add 5 more host, and it is very slow. Sometimes Rancher Server will Crash.

What’s the reason for this problem?
Thanks.

Rancher v1.6.14
Cattle v0.183.37
UI v1.6.37
Rancher CLI v0.6.7
Rancher Compose v0.12.5

4cpus 8G memory rancher server can’t manage 300 hosts? Who can tell me?