optimize(lb): rebalance when weights updated

pkg/discovery/discovery.go

@@ -79,17 +79,20 @@ func DefaultDiff(cacheKey string, prev, next Result) (Change, bool) {
 		},
 	}
 
-	prevMap := make(map[string]struct{}, len(prev.Instances))
+	prevMap := make(map[string]Instance, len(prev.Instances))
 	for _, ins := range prev.Instances {
-		prevMap[ins.Address().String()] = struct{}{}
+		prevMap[ins.Address().String()] = ins
 	}
 
-	nextMap := make(map[string]struct{}, len(next.Instances))
+	nextMap := make(map[string]Instance, len(next.Instances))
 	for _, ins := range next.Instances {
 		addr := ins.Address().String()
-		nextMap[addr] = struct{}{}
-		if _, found := prevMap[addr]; !found {
+		nextMap[addr] = ins
+		// FIXME(jizhuozhi): tags should also be used to determine whether the instance has updated
+		if prevIns, found := prevMap[addr]; !found {
 			ch.Added = append(ch.Added, ins)
+		} else if prevIns.Weight() != ins.Weight() {
+			ch.Updated = append(ch.Updated, ins)
 		}
 	}
 
@@ -98,7 +101,7 @@ func DefaultDiff(cacheKey string, prev, next Result) (Change, bool) {
 			ch.Removed = append(ch.Removed, ins)
 		}
 	}
-	return ch, len(ch.Added)+len(ch.Removed) != 0
+	return ch, len(ch.Added)+len(ch.Updated)+len(ch.Removed) != 0
 }
 
 type instance struct {
@@ -120,6 +123,10 @@ func (i *instance) Tag(key string) (value string, exist bool) {
 	return
 }
 
+func (i *instance) Tags() map[string]string {
+	return i.tags
+}
+
 // NewInstance creates a Instance using the given network, address and tags
 func NewInstance(network, address string, weight int, tags map[string]string) Instance {
 	return &instance{

pkg/discovery/discovery_test.go

@@ -47,17 +47,18 @@ func TestDefaultDiff(t *testing.T) {
 			Instances: []Instance{
 				NewInstance("tcp", "1", 10, nil),
 				NewInstance("tcp", "2", 10, nil),
-				NewInstance("tcp", "3", 10, nil),
+				NewInstance("tcp", "3", 20, nil),
 				NewInstance("tcp", "5", 10, nil),
 			},
 		}}, Change{
 			Result: Result{Instances: []Instance{
 				NewInstance("tcp", "1", 10, nil),
 				NewInstance("tcp", "2", 10, nil),
-				NewInstance("tcp", "3", 10, nil),
+				NewInstance("tcp", "3", 20, nil),
 				NewInstance("tcp", "5", 10, nil),
 			}, CacheKey: "1", Cacheable: true},
 			Added:   []Instance{NewInstance("tcp", "5", 10, nil)},
+			Updated: []Instance{NewInstance("tcp", "3", 20, nil)},
 			Removed: []Instance{NewInstance("tcp", "4", 10, nil)},
 		}, true},
 	}