I am seeking for the best solution for WAN link failover at our organization environment where has two WAN link connections(each MPLS type WAN link and Internet link having Zscaler proxy service via GRE tunnel) as below picture.
The goal that I'm trying to achieve is use MPLS WAN link as the primary to the Internet and the Internet access is redirected to Internet link(Zscaler proxy) when the primary link goes down.
*Currently, SDWAN Edge router is receiving the default route from only MPLS WAN link, not using Internet links for service vpn.
I just guess if I add one more default route using Internet link(Zscaler proxy), but how can I make MPLS link is the primary and Zscaler GRE link is as the secondary?
what do you mean "receiving default from MPLS" ? If you mean underlay network, then the 2nd default route does not make problem.
In SD-WAN, one interface can't use next-hop over another interface.
If you mean for overlay (receiving via OMP), then you may do primary/secondary failover just with increasing administrative distance for zscaler. I hope, you tunnel interface for zscaler in service-side VPN, then you may add default route but with higher admin. distance.