add relay proxy

pkg/chain/node.go

@@ -76,12 +76,12 @@ func (g *NodeGroup) Next() *Node {
 		return nil
 	}
 
-	selector := g.selector
-	if selector == nil {
-		return g.nodes[0]
+	s := g.selector
+	if s == nil {
+		s = DefaultSelector
 	}
 
-	return selector.Select(g.nodes...)
+	return s.Select(g.nodes...)
 }
 
 type FailMarker struct {

pkg/chain/selector.go

@@ -14,6 +14,10 @@ const (
 	DefaultFailTimeout = 30 * time.Second
 )
 
+var (
+	DefaultSelector = NewSelector(RoundRobinStrategy())
+)
+
 type Selector interface {
 	Select(nodes ...*Node) *Node
 }