--- a/src/http/ngx_http_upstream_round_robin.c
+++ b/src/http/ngx_http_upstream_round_robin.c
@@ -9,6 +9,7 @@
 #include <ngx_http.h>
 
 
+static int ngx_http_upstream_cmp_servers(const void *one, const void *two);
 static ngx_uint_t
 ngx_http_upstream_get_peer(ngx_http_upstream_rr_peers_t *peers);
 
@@ -20,15 +21,20 @@ ngx_http_upstream_init_round_robin(ngx_c
     ngx_url_t                      u;
     ngx_uint_t                     i, j, n;
     ngx_http_upstream_server_t    *server;
-    ngx_http_upstream_rr_peers_t  *peers;
+    ngx_http_upstream_rr_peers_t  *peers, *backup;
 
     us->peer.init = ngx_http_upstream_init_round_robin_peer;
 
     if (us->servers) {
-        n = 0;
         server = us->servers->elts;
 
+        n = 0;
+
         for (i = 0; i < us->servers->nelts; i++) {
+            if (server[i].backup) {
+                continue;
+            }
+
             n += server[i].naddrs;
         }
 
@@ -38,6 +44,7 @@ ngx_http_upstream_init_round_robin(ngx_c
             return NGX_ERROR;
         }
 
+        peers->single = (n == 1);
         peers->number = n;
         peers->name = &us->host;
 
@@ -45,20 +52,81 @@ ngx_http_upstream_init_round_robin(ngx_c
 
         for (i = 0; i < us->servers->nelts; i++) {
             for (j = 0; j < server[i].naddrs; j++) {
+                if (server[i].backup) {
+                    continue;
+                }
+
                 peers->peer[n].sockaddr = server[i].addrs[j].sockaddr;
                 peers->peer[n].socklen = server[i].addrs[j].socklen;
                 peers->peer[n].name = server[i].addrs[j].name;
-                peers->peer[n].weight = server[i].weight;
-                peers->peer[n].current_weight = server[i].weight;
                 peers->peer[n].max_fails = server[i].max_fails;
                 peers->peer[n].fail_timeout = server[i].fail_timeout;
                 peers->peer[n].down = server[i].down;
+                peers->peer[n].weight = server[i].down ? 0 : server[i].weight;
+                peers->peer[n].current_weight = peers->peer[n].weight;
                 n++;
             }
         }
 
         us->peer.data = peers;
 
+        ngx_sort(&peers->peer[0], (size_t) n,
+                 sizeof(ngx_http_upstream_rr_peer_t),
+                 ngx_http_upstream_cmp_servers);
+
+        /* backup servers */
+
+        n = 0;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            if (!server[i].backup) {
+                continue;
+            }
+
+            n += server[i].naddrs;
+        }
+
+        if (n == 0) {
+            return NGX_OK;
+        }
+
+        backup = ngx_pcalloc(cf->pool, sizeof(ngx_http_upstream_rr_peers_t)
+                              + sizeof(ngx_http_upstream_rr_peer_t) * (n - 1));
+        if (backup == NULL) {
+            return NGX_ERROR;
+        }
+
+        peers->single = 0;
+        backup->single = 0;
+        backup->number = n;
+        backup->name = &us->host;
+
+        n = 0;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            for (j = 0; j < server[i].naddrs; j++) {
+                if (!server[i].backup) {
+                    continue;
+                }
+
+                backup->peer[n].sockaddr = server[i].addrs[j].sockaddr;
+                backup->peer[n].socklen = server[i].addrs[j].socklen;
+                backup->peer[n].name = server[i].addrs[j].name;
+                backup->peer[n].weight = server[i].weight;
+                backup->peer[n].current_weight = server[i].weight;
+                backup->peer[n].max_fails = server[i].max_fails;
+                backup->peer[n].fail_timeout = server[i].fail_timeout;
+                backup->peer[n].down = server[i].down;
+                n++;
+            }
+        }
+
+        peers->next = backup;
+
+        ngx_sort(&backup->peer[0], (size_t) n,
+                 sizeof(ngx_http_upstream_rr_peer_t),
+                 ngx_http_upstream_cmp_servers);
+
         return NGX_OK;
     }
 
@@ -95,6 +163,7 @@ ngx_http_upstream_init_round_robin(ngx_c
         return NGX_ERROR;
     }
 
+    peers->single = (n == 1);
     peers->number = n;
     peers->name = &us->host;
 
@@ -113,10 +182,24 @@ ngx_http_upstream_init_round_robin(ngx_c
 
     us->peer.data = peers;
 
+    /* implicitly defined upstream has no backup servers */
+
     return NGX_OK;
 }
 
 
+static int
+ngx_http_upstream_cmp_servers(const void *one, const void *two)
+{
+    ngx_http_upstream_rr_peer_t  *first, *second;
+
+    first = (ngx_http_upstream_rr_peer_t *) one;
+    second = (ngx_http_upstream_rr_peer_t *) two;
+
+    return (first->weight < second->weight);
+}
+
+
 ngx_int_t
 ngx_http_upstream_init_round_robin_peer(ngx_http_request_t *r,
     ngx_http_upstream_srv_conf_t *us)
@@ -171,11 +254,13 @@ ngx_http_upstream_get_round_robin_peer(n
 {
     ngx_http_upstream_rr_peer_data_t  *rrp = data;
 
-    time_t                        now;
-    uintptr_t                     m;
-    ngx_uint_t                    i, n;
-    ngx_connection_t             *c;
-    ngx_http_upstream_rr_peer_t  *peer;
+    time_t                         now;
+    uintptr_t                      m;
+    ngx_int_t                      rc;
+    ngx_uint_t                     i, n;
+    ngx_connection_t              *c;
+    ngx_http_upstream_rr_peer_t   *peer;
+    ngx_http_upstream_rr_peers_t  *peers;
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                    "get rr peer, try: %ui", pc->tries);
@@ -207,7 +292,7 @@ ngx_http_upstream_get_round_robin_peer(n
     pc->cached = 0;
     pc->connection = NULL;
 
-    if (rrp->peers->number == 1) {
+    if (rrp->peers->single) {
         peer = &rrp->peers->peer[0];
 
     } else {
@@ -319,19 +404,53 @@ ngx_http_upstream_get_round_robin_peer(n
 
     /* ngx_unlock_mutex(rrp->peers->mutex); */
 
+    if (pc->tries == 1 && rrp->peers->next) {
+        pc->tries += rrp->peers->next->number;
+
+        n = rrp->peers->next->number / (8 * sizeof(uintptr_t)) + 1;
+        for (i = 0; i < n; i++) {
+             rrp->tried[i] = 0;
+        }
+    }
+
     return NGX_OK;
 
 failed:
 
+    peers = rrp->peers;
+
+    if (peers->next) {
+
+        /* ngx_unlock_mutex(peers->mutex); */
+
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, pc->log, 0, "backup servers");
+
+        rrp->peers = peers->next;
+        pc->tries = rrp->peers->number;
+
+        n = rrp->peers->number / (8 * sizeof(uintptr_t)) + 1;
+        for (i = 0; i < n; i++) {
+             rrp->tried[i] = 0;
+        }
+
+        rc = ngx_http_upstream_get_round_robin_peer(pc, rrp);
+
+        if (rc != NGX_BUSY) {
+            return rc;
+        }
+
+        /* ngx_lock_mutex(peers->mutex); */
+    }
+
     /* all peers failed, mark them as live for quick recovery */
 
-    for (i = 0; i < rrp->peers->number; i++) {
-        rrp->peers->peer[i].fails = 0;
+    for (i = 0; i < peers->number; i++) {
+        peers->peer[i].fails = 0;
     }
 
-    /* ngx_unlock_mutex(rrp->peers->mutex); */
+    /* ngx_unlock_mutex(peers->mutex); */
 
-    pc->name = rrp->peers->name;
+    pc->name = peers->name;
 
     return NGX_BUSY;
 }
@@ -410,7 +529,7 @@ ngx_http_upstream_free_round_robin_peer(
 
     /* TODO: NGX_PEER_KEEPALIVE */
 
-    if (rrp->peers->number == 1) {
+    if (rrp->peers->single) {
         pc->tries = 0;
         return;
     }