proxy: shuffle endpoints

Shuffle endpoitns to avoid being "stuck" to a single cluster member.

Documentation/proxy.md

@@ -4,6 +4,8 @@ etcd can now run as a transparent proxy. Running etcd as a proxy allows for easi
 
 etcd currently supports two proxy modes: `readwrite` and `readonly`. The default mode is `readwrite`, which forwards both read and write requests to the etcd cluster. A `readonly` etcd proxy only forwards read requests to the etcd cluster, and returns `HTTP 501` to all write requests. 
 
+etcd will shuffle the list of cluster members periodically to avoid sending all connections to a single member.
+
 ### Using an etcd proxy
 To start etcd in proxy mode, you need to provide three flags: `proxy`, `listen-client-urls`, and `initial-cluster` (or `discovery`). 
 

proxy/director.go

@@ -16,6 +16,7 @@ package proxy
 
 import (
 	"log"
+	"math/rand"
 	"net/url"
 	"sync"
 	"time"
@@ -65,6 +66,13 @@ func (d *director) refresh() {
 		}
 		endpoints = append(endpoints, newEndpoint(*uu))
 	}
+
+	// shuffle array to avoid connections being "stuck" to a single endpoint
+	for i := range endpoints {
+		j := rand.Intn(i + 1)
+		endpoints[i], endpoints[j] = endpoints[j], endpoints[i]
+	}
+
 	d.ep = endpoints
 }