check etcd servers by a random order

Kubernetes-commit: ea627f987507de38dfc46ab2d9c924690eba5ee9

pkg/storage/etcd3/preflight/checks.go

@@ -18,6 +18,7 @@ package preflight
 
 import (
 	"fmt"
+	"math/rand"
 	"net"
 	"net/url"
 	"time"
@@ -59,9 +60,11 @@ func parseServerURI(serverURI string) (*url.URL, error) {
 // CheckEtcdServers will attempt to reach all etcd servers once. If any
 // can be reached, return true.
 func (con EtcdConnection) CheckEtcdServers() (done bool, err error) {
-	// Attempt to reach every Etcd server in order
-	for _, serverURI := range con.ServerList {
-		host, err := parseServerURI(serverURI)
+	// Attempt to reach every Etcd server randomly.
+	serverNumber := len(con.ServerList)
+	serverPerms := rand.Perm(serverNumber)
+	for _, index := range serverPerms {
+		host, err := parseServerURI(con.ServerList[index])
 		if err != nil {
 			return false, err
 		}