Add resolution and examples for analzyer. (#5729)

content/en/docs/reference/config/analysis/ist0109/index.md

@@ -3,10 +3,92 @@ title: ConflictingMeshGatewayVirtualServiceHosts
 layout: analysis-message
 ---
 
-This message occurs when Istio detects an overlap between virtual service
-resources. For example, you have multiple virtual services defined to use the
-same hostname and gateway, where the gateway is set to `mesh` or no gateway
-specified.
+This message occurs when Istio detects an overlap between
+[virtual service](/docs/reference/config/networking/virtual-service)
+resources that conflict with one another. For example, multiple virtual
+services defined to use the same hostname and attached to a mesh gateway
+will generate an error message. Note that Istio supports merging of virtual
+services that are attached to the ingress gateways.
 
-To resolve this problem, check your Istio configuration, remove the conflicting
-values and try again.
+## Resolution
+
+To resolve this issue, you can take one of the following actions:
+
+* Merge the conflicting virtual services into a single resource.
+* Make the hostnames unique across virtual services attached to a mesh gateway.
+* Scope the resource to a specific namespace by setting the `exportTo` field.
+
+## Examples
+
+The `productpage` virtual service in namespace `team1` conflicts with the
+`custom` virtual service in `team2` namespace because both of the following
+are true:
+
+* They are attached to the default "mesh" gateway as no custom gateway is
+specified.
+* They both define the same host `productpage.default.svc.cluster.local`.
+
+{{< text yaml >}}
+apiVersion: networking.istio.io/v1alpha3
+kind: VirtualService
+metadata:
+  name: productpage
+  namespace: team-1
+spec:
+  hosts:
+  - productpage.default.svc.cluster.local
+  http:
+  - route:
+    - destination:
+        host: productpage
+---
+apiVersion: networking.istio.io/v1alpha3
+kind: VirtualService
+metadata:
+  name: custom
+  namespace: team-2
+spec:
+  hosts:
+  - productpage.default.svc.cluster.local
+  http:
+  - route:
+    - destination:
+        host: productpage.team-2.svc.cluster.local
+---
+{{< /text >}}
+
+You can resolve this issue by setting the `exportTo` field to `.` so
+that each virtual service is scoped only to its own namespace:
+
+{{< text yaml >}}
+apiVersion: networking.istio.io/v1alpha3
+kind: VirtualService
+metadata:
+  name: productpage
+  namespace: team-1
+spec:
+  exportTo:
+  - "."
+  hosts:
+  - productpage.default.svc.cluster.local
+  http:
+  - route:
+    - destination:
+        host: productpage
+---
+apiVersion: networking.istio.io/v1alpha3
+kind: VirtualService
+metadata:
+  name: custom
+  namespace: team-2
+spec:
+  exportTo:
+  - "."
+  hosts:
+  - productpage.default.svc.cluster.local
+  http:
+  - route:
+    - destination:
+        host: productpage.team-2.svc.cluster.local
+---
+{{< /text >}}