In case you do not have a static IPv4 address assigned to your WAN interface, you can use a free Dynamic DNS service to use a domain name that is always resolving to your current dynamic IP address. This article can be applied to USG FLEX & Nebula Security Gateway
Navigate to the Site-wide -> Configure -> Firewall -> Firewall settings
- Please navigate on the left-hand side to Security Gateway > Configure > Interface Addressing
- This is an example of how to set up the free Dynu DDNS:
In case your WAN1 interface is failing, you can set up WAN2 as the backup interface to take over the DDNS role.