diff --git a/registry/registry.go b/registry/registry.go
index 7046bafce..6e35ff7b9 100644
--- a/registry/registry.go
+++ b/registry/registry.go
@@ -1,6 +1,9 @@
 package registry
 
-import "context"
+import (
+	"context"
+	"sort"
+)
 
 // Registrar is service registrar.
 type Registrar interface {
@@ -45,3 +48,43 @@ type ServiceInstance struct {
 	//   grpc://127.0.0.1:9000?isSecure=false
 	Endpoints []string `json:"endpoints"`
 }
+
+// Equal returns whether i and o are equivalent.
+func (i *ServiceInstance) Equal(o interface{}) bool {
+	if i == nil && o == nil {
+		return true
+	}
+
+	if i == nil || o == nil {
+		return false
+	}
+
+	t, ok := o.(*ServiceInstance)
+	if !ok {
+		return false
+	}
+
+	if len(i.Endpoints) != len(t.Endpoints) {
+		return false
+	}
+
+	sort.Strings(i.Endpoints)
+	sort.Strings(t.Endpoints)
+	for j := 0; j < len(i.Endpoints); j++ {
+		if i.Endpoints[j] != t.Endpoints[j] {
+			return false
+		}
+	}
+
+	if len(i.Metadata) != len(t.Metadata) {
+		return false
+	}
+
+	for k, v := range i.Metadata {
+		if v != t.Metadata[k] {
+			return false
+		}
+	}
+
+	return i.ID == t.ID && i.Name == t.Name && i.Version == t.Version
+}