Update application gateway routing notes

Added note about WAF request forwarding when no backend pool members are available.

Signed-off-by: MJyot <[email protected]>

Author: MJyot

articles/application-gateway/how-application-gateway-works.md

@@ -36,8 +36,7 @@ If a request is valid and not blocked by WAF, the application gateway evaluates
 
 Based on the request routing rule, the application gateway determines whether to route all requests on the listener to a specific backend pool, route requests to different backend pools based on the URL path, or redirect requests to another port or external site.
 > [!NOTE]
-> Rules are processed in the order they're listed in the portal for v1 SKU. 
-
+> Rules are processed in the order they're listed in the portal for v1 SKU.
 When the application gateway selects the backend pool, it sends the request to one of the healthy backend servers in the pool (y.y.y.y). The health of the server is determined by a health probe. If the backend pool contains multiple servers, the application gateway uses a round-robin algorithm to route the requests between healthy servers. This load balances the requests on the servers.
 
 After the application gateway determines the backend server, it opens a new TCP session with the backend server based on HTTP settings. HTTP settings specify the protocol, port, and other routing-related settings that are required to establish a new session with the backend server.
@@ -46,6 +45,9 @@ The port and protocol used in HTTP settings determine whether the traffic betwee
 
 When an application gateway sends the original request to the backend server, it honors any custom configuration made in the HTTP settings related to overriding the hostname, path, and protocol. This action maintains cookie-based session affinity, connection draining, host-name selection from the backend, and so on.
 
+> [!NOTE]
+> Application Gateway does not forward the request to WAF when no backend pool members are available
+
  > [!NOTE]
 > If the backend pool:
 > - **Is a public endpoint**, the application gateway uses its frontend public IP to reach the server. If there isn't a frontend public IP address, one is assigned for the outbound external connectivity.