AG ingress ignores changes to default backend

[shirolimit]

Describe the bug Application gateway ignores k8s events related to defaultBackend pods/endpoints. As a result, it doesn't update the backend pool target address on pod recreation.

To Reproduce

1. Enable Azure ingress in the cluster
2. Apply the following yaml:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: my-nginx
     labels:
       app.kubernetes.io/name: "my-nginx"
   spec:
     replicas: 1
     selector:
       matchLabels:
         app.kubernetes.io/name: "my-nginx"
     template:
       metadata:
         labels:
           app.kubernetes.io/name: "my-nginx"
       spec:
         containers:
           - name: nginx
             image: nginx:1.20
             ports:
               - containerPort: 80
                 name: http
   ---
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: default-nginx
     labels:
       app.kubernetes.io/name: "default-nginx"
   spec:
     replicas: 1
     selector:
       matchLabels:
         app.kubernetes.io/name: "default-nginx"
     template:
       metadata:
         labels:
           app.kubernetes.io/name: "default-nginx"
       spec:
         containers:
           - name: nginx
             image: nginx:1.21
             ports:
               - containerPort: 80
                 name: http
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: default-service
   spec:
     ports:
       - name: http
         protocol: TCP
         port: 80
         targetPort: http
     selector:
       app.kubernetes.io/name: "default-nginx"
     type: ClusterIP
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
   spec:
     ports:
       - name: http
         protocol: TCP
         port: 8080
         targetPort: http
     selector:
       app.kubernetes.io/name: "my-nginx"
     type: ClusterIP
   ---
   apiVersion: networking.k8s.io/v1
   kind: Ingress
   metadata:
     name: test-ingress
     annotations:
       kubernetes.io/ingress.class: azure/application-gateway
       appgw.ingress.kubernetes.io/backend-path-prefix: "/"
   spec:
     defaultBackend:
       service:
         name: default-service
         port:
           number: 80
     rules:
       - http:
           paths:
             - path: /test-my-ingress/*
               pathType: Prefix
               backend:
                 service:
                   name: my-service
                   port:
                     number: 8080
   
   

3. Check that both services work
4. Restart default-nginx: kubectl rollout restart deployment/default-nginx
5. Wait 30 seconds
6. Make sure that default backend is not accessible and AG returns 502/504

Ingress Controller details

• describe

How to fix

Add

for _, ingress := range c.ListHTTPIngresses() {
	defaultBackend := ingress.Spec.DefaultBackend
	if defaultBackend != nil && (defaultBackend.Service.Name == service.Name) {
		return true
	}

	// ...
}

to https://github.com/Azure/application-gateway-kubernetes-ingress/blob/master/pkg/k8scontext/context.go#L850-L866

At the moment it only cares about rules.