Port Forwarding for Web Server

Hello Everyone!!

Greetings for the day!!

I have logged in this forum from quite long time but I didn't use it much. I am back here after long time with one query.

Network Setup:

1. We have one Fortigate deployed as gateway level and there are 2 WAN links terminated on it from different ISPs.

2. Public IP from ISP1 is 1.1.1.1 and Public IP from ISP2 is 2.2.2.2 (I am using these IPs as reference only).

3. We have one web server hosted in LAN side of Fortigate whose private IP is 10.10.10.10 and domain xyz.com (For example) has been registered with public IP 1.1.1.1 for this web server. We have also done port forwarding (1.1.1.1 mapped to 10.10.10.10 for port 80) on Fortigate to allow incoming web traffic.

Requirement:

1. As of now when we do nslookup for xyz.com it resolves IP 1.1.1.1.

2. But when ISP1 goes down, it should be automatically resolve with IP 2.2.2.2.

3. I am not sure whether this can be achieved by adding IP 2.2.2.2 in A-record of DNS of Domain Registrar as backup along with IP 1.1.1.1.

4. As of now when ISP1 goes down, we have to access our web server through 2.2.2.2 only. We have already done port forwarding for 2.2.2.2 IP.

Can anyone suggest how I can keep my website UP with ISP2 IP when ISP1 gateway is DOWN? Once ISP1 is UP again, website should be accessible again with ISP1 IP only.

I don't have too much idea of domain registration part and DNS records; still trying to learn by searching on Internet..

Thanks a lot in advance..

Regards,
Vivek Abhani