Varnish controller updates service instance addresses when necessary.

That is, when the addresses are not stored in the controller's
internal data structures.

pkg/varnish/varnish.go

@@ -654,6 +654,17 @@ func (vc *Controller) updateBeGauges() {
 	beEndpsGauge.Set(float64(nBeEndps))
 }
 
+func (vc *Controller) setInstAddrs(svc *varnishSvc, addrs []vcl.Address) {
+	for i, addr := range addrs {
+		svc.instances[i] = &varnishInst{
+			ns:     addr.PodNamespace,
+			name:   addr.PodName,
+			addr:   addr.Address(),
+			admMtx: &sync.Mutex{},
+		}
+	}
+}
+
 // Update a Varnish Service to implement an configuration.
 //
 //	svcKey: namespace/name key for the Service
@@ -680,21 +691,17 @@ func (vc *Controller) Update(
 		}
 	}
 	svc, exists := vc.svcs[svcKey]
-	if !exists {
+	if !exists || svc == nil {
 		svc = &varnishSvc{
 			instances: make([]*varnishInst, len(addrs)),
 		}
-		for i, addr := range addrs {
-			svc.instances[i] = &varnishInst{
-				ns:     addr.PodNamespace,
-				name:   addr.PodName,
-				addr:   addr.Address(),
-				admMtx: &sync.Mutex{},
-			}
-		}
+		vc.setInstAddrs(svc, addrs)
 		vc.svcs[svcKey] = svc
 		svcsGauge.Inc()
 		vc.log.Infof("Added Varnish service definition %s", svcKey)
+	} else if len(svc.instances) == 0 {
+		svc.instances = make([]*varnishInst, len(addrs))
+		vc.setInstAddrs(svc, addrs)
 	}
 	svc.cfgLoaded = false
 	if svc.spec == nil {