Sample /etc/network/interfaces with static IP for proxmox VM

interfaces

# Notes:
# remove the first line (source) if interfaces.d does not exist.
# interface_name examples: eth0, ens18 etc
# chosen_ip example: 192.168.1.18 etc
# This works for VMs. For LXC, it has to be done within proxmox itself.
# On UI: node > CT > network. Enter IP there with a trailing "/24".

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface (static)
allow-hotplug <interface_name>
auto <interface_name>
iface <interface_name> inet static
    address <chosen_ip>
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 1.1.1.1 9.9.9.9 8.8.8.8