azure gateway as priority traffic manager

Question

We have a set-up an azure gateway of tier WAF V2 (so it would be zone-redundant). It has a backend pool containing 2 WebApps -AppServices (supposedly a Primary and a Secondary).

The idea behind it was to use the gateway similarly to priority traffic manager: Routing usually to the primary WebApp, and only routing to the secondary WebApp in case the first one goes down.

The Problem is that the only way I found to do that is to order the rules associated with the listeners of the backend pool (because I believe azure prioritizes them according to the order they are listed). But given that both Apps are in the same backend pool, Im unsure of how to do that.

So now the gateway randomly routes to either the first or second WebApp.

Any advice or suggestions would be much appreciated,

Thank you

Note: Also we have tried setting a traffic manager in between the gateway and the WebApps, but the gateway keeps connecting to the primary WebApp even when its down and its probe becomes of health status unknown.

Answer 1

Application Gateway is a layer 7 load balancer, which means it works with web traffic only (HTTP/HTTPS/WebSocket). It supports capabilities such as SSL termination, cookie-based session affinity, and round robin for load balancing traffic. This indicated that the application gateway frontend randomly distribute the incoming traffics to the endpoint if both endpoints are healthy. So you could see the gateway randomly routes to either the first or second WebApp. See the application gateway FAQ. The app gateway does not work like priority-based traffic manager which always requests to the primary web app unless the primary web app is unhealthy.

About the health status unknown, the most common reason is that access to the backend is being blocked by an NSG or custom DNS. Ref: Troubleshooting bad gateway errors in Application Gateway