Ubuntu 16 Server cannot get wifi configured correctly to work with WPA2

To scan all Wifi networks try using the command sudo iwlist scan

wlan0    unassociated  Nickname:"rtl_wifi"
         Mode:Managed  Access Point: Not-Associated   Sensitivity:0/0
         Retry:off   RTS thr:off   Fragment thr:off
         Power Management:off
         Link Quality:0  Signal level:0  Noise level:0
         Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
         Tx excessive retries:0  Invalid misc:0   Missed beacon:0

You can connect to your WPA2 access point by putting the following in /etc/network/interfaces

auto wlan0
iface wlan0 inet dhcp
wpa-ssid <your_router>
wpa-psk <your_wpa_key>

Get the system to read and use the changes:

sudo ifdown wlan0 && sudo ifup -v wlan0