Fix defaultServer backend update for Ingress with defaultBackend. (#8825)

internal/ingress/controller/controller.go

@@ -1208,17 +1208,15 @@ func (n *NGINXController) createServers(data []*ingress.Ingress,
 				// use backend specified in Ingress as the default backend for all its rules
 				un = backendUpstream.Name
 
-				// special "catch all" case, Ingress with a backend but no rule
 				defLoc := servers[defServerName].Locations[0]
-				defLoc.Backend = backendUpstream.Name
-				defLoc.Service = backendUpstream.Service
-				defLoc.Ingress = ing
-
 				if defLoc.IsDefBackend && len(ing.Spec.Rules) == 0 {
 					klog.V(2).Infof("Ingress %q defines a backend but no rule. Using it to configure the catch-all server %q", ingKey, defServerName)
 
 					defLoc.IsDefBackend = false
-
+					// special "catch all" case, Ingress with a backend but no rule
+					defLoc.Backend = backendUpstream.Name
+					defLoc.Service = backendUpstream.Service
+					defLoc.Ingress = ing
 					// TODO: Redirect and rewrite can affect the catch all behavior, skip for now
 					originalRedirect := defLoc.Redirect
 					originalRewrite := defLoc.Rewrite

test/e2e/ingress/without_host.go

@@ -93,5 +93,13 @@ var _ = framework.IngressNginxDescribe("[Ingress] definition without host", func
 			WithHeader("Host", "only-backend").
 			Expect().
 			Status(http.StatusOK)
+		// Following assertion added with respect to issue https://github.com/kubernetes/ingress-nginx/issues/8823
+		// This check ensure that ingress having defaultBackend with rules should only be added as default backend
+		// for the host mentioned in rule. It should not affect the default catch-all server_name _ block.
+		f.HTTPTestClient().
+			GET("/").
+			WithHeader("Host", "only-backend-doesnotexist").
+			Expect().
+			Status(http.StatusNotFound)
 	})
 })