I notice you guys are using Ubuntu 18.04 server, so you may have already solved this. But it took me forever to figure out how to set a static IP. It’s different than 16.04 or 14.04.
You edit a file called /etc/netplan/01-netcfg.yaml and put in whatever static IP information is right for your server.
network: version: 2 renderer: networkd ethernets: ens160: (or whatever your interface is called) dhcp4: no addresses: [192.168.1.19/24] gateway4: 192.168.1.1 nameservers: addresses: [192.168.1.1]
Then you run this command
sudo netplan apply
I hope this has been helpful!