You have an Azure Application Gateway configured for a single site at https://www.contoso.com. The gateway has one backend pool with two backend servers and a single routing rule. Each backend server also hosts another site that listens on port 8080. You must ensure that if port 8080 on one backend server becomes unavailable, all traffic for https://www.contoso.com is sent to the remaining healthy backend server. What should you configure?

To ensure traffic is redirected when a backend server's port 8080 becomes unavailable, you must configure a health probe. Application Gateway uses health probes to monitor the health of backend instances. By creating a custom health probe that specifically checks port 8080 on your backend servers, the Application Gateway can detect when a server is unhealthy on that port and automatically route traffic away from it to the healthy server. Adding a new routing rule or changing the listener port would not address the health monitoring requirement. Adding a second listener is also not necessary for this specific problem, as the existing listener is already configured for the site.