update ipvs proxier to update realserver weights at startup

Update the IPVS proxier to have a bool `initialSync` which is set to
true when a new proxier is initialized and then set to false on all
syncs. This lets us run startup-only logic, which subsequently lets us
update the realserver only when needed and avoiding any expensive
operations.

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

pkg/proxy/ipvs/proxier.go

@@ -223,6 +223,13 @@ type Proxier struct {
 	serviceMap   proxy.ServiceMap
 	endpointsMap proxy.EndpointsMap
 	nodeLabels   map[string]string
+	// initialSync is a bool indicating if the proxier is syncing for the first time.
+	// It is set to true when a new proxier is initialized and then set to false on all
+	// future syncs.
+	// This lets us run specific logic that's required only during proxy startup.
+	// For eg: it enables us to update weights of existing destinations only on startup
+	// saving us the cost of querying and updating real servers during every sync.
+	initialSync bool
 	// endpointSlicesSynced, and servicesSynced are set to true when
 	// corresponding objects are synced after startup. This is used to avoid updating
 	// ipvs rules with some partial data after kube-proxy restart.
@@ -468,6 +475,7 @@ func NewProxier(ipt utiliptables.Interface,
 		serviceChanges:        proxy.NewServiceChangeTracker(newServiceInfo, ipFamily, recorder, nil),
 		endpointsMap:          make(proxy.EndpointsMap),
 		endpointsChanges:      proxy.NewEndpointChangeTracker(hostname, nil, ipFamily, recorder, nil),
+		initialSync:           true,
 		syncPeriod:            syncPeriod,
 		minSyncPeriod:         minSyncPeriod,
 		excludeCIDRs:          parsedExcludeCIDRs,
@@ -1010,6 +1018,12 @@ func (proxier *Proxier) syncProxyRules() {
 		return
 	}
 
+	// its safe to set initialSync to false as it acts as a flag for startup actions
+	// and the mutex is held.
+	defer func() {
+		proxier.initialSync = false
+	}()
+
 	// Keep track of how long syncs take.
 	start := time.Now()
 	defer func() {
@@ -2007,6 +2021,19 @@ func (proxier *Proxier) syncEndpoint(svcPortName proxy.ServicePortName, onlyNode
 		}
 
 		if curEndpoints.Has(ep) {
+			// if we are syncing for the first time, loop through all current destinations and
+			// reset their weight.
+			if proxier.initialSync {
+				for _, dest := range curDests {
+					if dest.Weight != newDest.Weight {
+						err = proxier.ipvs.UpdateRealServer(appliedVirtualServer, newDest)
+						if err != nil {
+							klog.ErrorS(err, "Failed to update destination", "newDest", newDest)
+							continue
+						}
+					}
+				}
+			}
 			// check if newEndpoint is in gracefulDelete list, if true, delete this ep immediately
 			uniqueRS := GetUniqueRSName(vs, newDest)
 			if !proxier.gracefuldeleteManager.InTerminationList(uniqueRS) {
@@ -2025,6 +2052,7 @@ func (proxier *Proxier) syncEndpoint(svcPortName proxy.ServicePortName, onlyNode
 			continue
 		}
 	}
+
 	// Delete old endpoints
 	for _, ep := range curEndpoints.Difference(newEndpoints).UnsortedList() {
 		// if curEndpoint is in gracefulDelete, skip