We started to use the built-in firewall function in our Proxmox cluster, and sometimes VM-s started to timeout for time to time, but we found no problem then. It happened again, and finally found the root of our problem.
The following line started to appear in the syslog (both VM, and core machine):
nf_conntrack: table full, dropping packetContinue reading “Proxmox VM’s have slow response times and timeouts”