Azure Application gateway is a regional load-balancing service that distributes traffic within virtual networks across virtual machines (VMs) or zonal and zone-redundant service endpoints within a region.
Whereas Azure Front Door is a global load-balancing service that distributes traffic across regional backends, clouds, or hybrid on-premises services to the closest available backend.
If your hub and spokes are in the same region and you want to load balance traffic between them, you can go with Azure Application gateway.
Refer : https://learn.microsoft.com/en-us/azure/architecture/high-availability/ref-arch-iaas-web-and-db
If your hub and spokes are in different regions and you want to load balance traffic between them, you can go with Azure Front Door.
Refer : https://learn.microsoft.com/en-us/azure/architecture/example-scenario/signalr/#azure-front-door
If you would like to load balance or route traffic within a virtual network or internally, you can use a combination of Application gateway and Front Door OR use the latest Azure Front Door Premium tier where you can enable Private Link to connect to origins behind an internal load balancer over a private endpoint.
Refer : https://learn.microsoft.com/en-us/azure/architecture/example-scenario/multi-saas/multitenant-saas
https://learn.microsoft.com/en-us/azure/frontdoor/private-link
So, it all comes down to your requirement. You can configure any of the below:
- 1 Application gateway to load balance the traffic in the same region
- 1 Azure Front Door to load balance traffic between different regions
- 2 Application gateways and 1 Azure Front Door Classic to load balance
internal traffic in different regions
- 1 Azure Front Door Premium with private endpoint to load balance internal traffic in different
regions