auto eth0
iface eth0 inet manual
    bond-master bond0
    bond-primary eth0
    bond-mode active-backup
   
auto wlan0
iface wlan0 inet manual
    wpa-ssid your_SSID
    wpa-psk xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

    # to generate proper encrypted key: wpa_passphrase your_SSID your_password

    bond-master bond0
    bond-primary eth0
    bond-mode active-backup
   
# Define master
auto bond0
iface bond0 inet dhcp
    bond-slaves none
    bond-primary eth0
    bond-mode active-backup
    bond-miimon 100