Limit webserver to one uplink when uplink balancing

Question

We have 2 uplinks. One is a fiber connection (static IP) the other is a cable modem connection (non static IP). I have uplink balancing enabled, which works great. The issue is the webserver initiates connections to outside resources. Sometimes things are not working like they should and when I turn off the cable modem connection we never have any issues. I suspect there are times where the server is initiating the connection to the outside resources from the cable modem uplink and it is getting rejected. Is there a way to have uplink balancing but force a webserver to only utilize one of the uplinks?

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timm0 · Answer

A while ago I had a similar issue. We had vendors who used a single IP address on the outside of our firewall as part of their system's security. So we had to make sure that all traffic to these vendors went through the interface to which the source IP address was assigned. 
 So I created a static route for the destination site to point to the default gateway related to the required interface's IP. If the interface IP was 10.1.1.100/24 and the ISP gateway was 10.1.1.1, I set the next hop for www.whatever.com to be 10.1.1.1. 
 May not be the most elegant or even the preferred approach, but it worked perfectly.