new file mode 100644
--- /dev/null
+++ b/src/http/ngx_http_upstream_round_robin.c
@@ -0,0 +1,430 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+ngx_int_t
+ngx_http_upstream_init_round_robin(ngx_conf_t *cf,
+    ngx_http_upstream_srv_conf_t *us)
+{
+    ngx_url_t                      u;
+    ngx_uint_t                     i, j, n;
+    ngx_http_upstream_server_t    *server;
+    ngx_http_upstream_rr_peers_t  *peers;
+
+    us->peer.init = ngx_http_upstream_init_round_robin_peer;
+
+    if (us->servers) {
+        n = 0;
+        server = us->servers->elts;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            n += server[i].naddrs;
+        }
+
+        peers = ngx_pcalloc(cf->pool, sizeof(ngx_http_upstream_rr_peers_t)
+                              + sizeof(ngx_http_upstream_rr_peer_t) * (n - 1));
+        if (peers == NULL) {
+            return NGX_ERROR;
+        }
+
+        peers->number = n;
+        peers->name = &us->host;
+
+        n = 0;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            for (j = 0; j < server[i].naddrs; j++) {
+                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;
+                n++;
+            }
+        }
+
+        us->peer.data = peers;
+
+        return NGX_OK;
+    }
+
+
+    /* an upstream implicitly defined by proxy_pass, etc. */
+
+    ngx_memzero(&u, sizeof(ngx_url_t));
+
+    u.host = us->host;
+    u.portn = us->port;
+
+    if (ngx_inet_resolve_host(cf, &u) != NGX_OK) {
+        if (u.err) {
+            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                          "%s in upstream host \"%V\" is not found in %s:%ui",
+                          u.err, &us->host, us->file_name.data, us->line);
+        }
+
+        return NGX_ERROR;
+    }
+
+    n = u.naddrs;
+
+    peers = ngx_pcalloc(cf->pool, sizeof(ngx_http_upstream_rr_peers_t)
+                              + sizeof(ngx_http_upstream_rr_peer_t) * (n - 1));
+    if (peers == NULL) {
+        return NGX_ERROR;
+    }
+
+    peers->number = n;
+    peers->name = &us->host;
+
+    n = 0;
+
+    for (i = 0; i < u.naddrs; i++) {
+        peers->peer[n].sockaddr = u.addrs[i].sockaddr;
+        peers->peer[n].socklen = u.addrs[i].socklen;
+        peers->peer[n].name = u.addrs[i].name;
+        peers->peer[n].weight = 1;
+        peers->peer[n].current_weight = 1;
+        peers->peer[n].max_fails = 1;
+        peers->peer[n].fail_timeout = 10;
+        n++;
+    }
+
+    us->peer.data = peers;
+
+    return NGX_OK;
+}
+
+
+ngx_int_t
+ngx_http_upstream_init_round_robin_peer(ngx_http_request_t *r,
+    ngx_http_upstream_srv_conf_t *us)
+{
+    ngx_uint_t                         n;
+    ngx_http_upstream_rr_peer_data_t  *rrp;
+
+    rrp = r->upstream->peer.data;
+
+    if (rrp == NULL) {
+        rrp = ngx_palloc(r->pool, sizeof(ngx_http_upstream_rr_peer_data_t));
+        if (rrp == NULL) {
+            return NGX_ERROR;
+        }
+
+        r->upstream->peer.data = rrp;
+    }
+
+    rrp->peers = us->peer.data;
+    rrp->current = 0;
+
+    if (rrp->peers->number <= 8 * sizeof(uintptr_t)) {
+        rrp->tried = &rrp->data;
+        rrp->data = 0;
+
+    } else {
+        n = (rrp->peers->number + (8 * sizeof(uintptr_t) - 1))
+                / (8 * sizeof(uintptr_t));
+
+        rrp->tried = ngx_pcalloc(r->pool, n * sizeof(uintptr_t));
+        if (rrp->tried == NULL) {
+            return NGX_ERROR;
+        }
+    }
+
+    r->upstream->peer.get = ngx_http_upstream_get_round_robin_peer;
+    r->upstream->peer.free = ngx_http_upstream_free_round_robin_peer;
+    r->upstream->peer.tries = rrp->peers->number;
+#if (NGX_HTTP_SSL)
+    r->upstream->peer.save_session = ngx_http_upstream_save_round_robin_peer;
+#endif
+
+    return NGX_OK;
+}
+
+
+ngx_int_t
+ngx_http_upstream_get_round_robin_peer(ngx_peer_connection_t *pc, void *data)
+{
+    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;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                   "get rr peer, try: %ui", pc->tries);
+
+    now = ngx_time();
+
+    /* ngx_lock_mutex(rrp->peers->mutex); */
+
+    if (rrp->peers->last_cached) {
+
+        /* cached connection */
+
+        c = rrp->peers->cached[rrp->peers->last_cached];
+        rrp->peers->last_cached--;
+
+        /* ngx_unlock_mutex(ppr->peers->mutex); */
+
+#if (NGX_THREADS)
+        c->read->lock = c->read->own_lock;
+        c->write->lock = c->write->own_lock;
+#endif
+
+        pc->connection = c;
+        pc->cached = 1;
+
+        return NGX_OK;
+    }
+
+    pc->cached = 0;
+    pc->connection = NULL;
+
+    if (rrp->peers->number == 1) {
+        peer = &rrp->peers->peer[0];
+
+    } else {
+
+        /* there are several peers */
+
+        if (pc->tries == rrp->peers->number) {
+
+            /* it's a first try - get a current peer */
+
+            for ( ;; ) {
+                rrp->current = rrp->peers->current;
+
+                n = rrp->current / (8 * sizeof(uintptr_t));
+                m = 1 << rrp->current % (8 * sizeof(uintptr_t));
+
+                if (!(rrp->tried[n] & m)) {
+                    peer = &rrp->peers->peer[rrp->current];
+
+                    if (!peer->down) {
+
+                        if (peer->max_fails == 0
+                            || peer->fails < peer->max_fails)
+                        {
+                            break;
+                        }
+
+                        if (now - peer->accessed > peer->fail_timeout) {
+                            peer->fails = 0;
+                            break;
+                        }
+
+                    } else {
+                        rrp->tried[n] |= m;
+                    }
+
+                    pc->tries--;
+                }
+
+                rrp->peers->current++;
+
+                if (rrp->peers->current >= rrp->peers->number) {
+                    rrp->peers->current = 0;
+                }
+
+                if (pc->tries) {
+                    continue;
+                }
+
+                goto failed;
+            }
+
+            peer->current_weight--;
+
+            if (peer->current_weight == 0) {
+                peer->current_weight = peer->weight;
+
+                rrp->peers->current++;
+
+                if (rrp->peers->current >= rrp->peers->number) {
+                    rrp->peers->current = 0;
+                }
+            }
+
+        } else {
+            for ( ;; ) {
+                n = rrp->current / (8 * sizeof(uintptr_t));
+                m = 1 << rrp->current % (8 * sizeof(uintptr_t));
+
+                if (!(rrp->tried[n] & m)) {
+
+                    peer = &rrp->peers->peer[rrp->current];
+
+                    if (!peer->down) {
+
+                        if (peer->max_fails == 0
+                            || peer->fails < peer->max_fails)
+                        {
+                            break;
+                        }
+
+                        if (now - peer->accessed > peer->fail_timeout) {
+                            peer->fails = 0;
+                            break;
+                        }
+
+                    } else {
+                        rrp->tried[n] |= m;
+                    }
+
+                    pc->tries--;
+                }
+
+                rrp->current++;
+
+                if (rrp->current >= rrp->peers->number) {
+                    rrp->current = 0;
+                }
+
+                if (pc->tries) {
+                    continue;
+                }
+
+                goto failed;
+            }
+
+            peer->current_weight--;
+
+            if (peer->current_weight == 0) {
+                peer->current_weight = peer->weight;
+
+                if (rrp->current == rrp->peers->current) {
+                    rrp->peers->current++;
+
+                    if (rrp->peers->current >= rrp->peers->number) {
+                        rrp->peers->current = 0;
+                    }
+                }
+            }
+        }
+
+        rrp->tried[n] |= m;
+    }
+
+    pc->sockaddr = peer->sockaddr;
+    pc->socklen = peer->socklen;
+    pc->name = &peer->name;
+#if (NGX_SSL)
+    pc->ssl_session = peer->ssl_session;
+#endif
+
+    /* ngx_unlock_mutex(rrp->peers->mutex); */
+
+    return NGX_OK;
+
+failed:
+
+    /* all peers failed, mark them as live for quick recovery */
+
+    for (i = 0; i < rrp->peers->number; i++) {
+        rrp->peers->peer[i].fails = 0;
+    }
+
+    /* ngx_unlock_mutex(rrp->peers->mutex); */
+
+    pc->name = rrp->peers->name;
+
+    return NGX_BUSY;
+}
+
+
+void
+ngx_http_upstream_free_round_robin_peer(ngx_peer_connection_t *pc, void *data,
+    ngx_uint_t state)
+{
+    ngx_http_upstream_rr_peer_data_t  *rrp = data;
+
+    time_t                       now;
+    ngx_http_upstream_rr_peer_t  *peer;
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                   "free rr peer %ui %ui", pc->tries, state);
+
+    if (state == 0 && pc->tries == 0) {
+        return;
+    }
+
+    /* TODO: NGX_PEER_KEEPALIVE */
+
+    if (rrp->peers->number == 1) {
+        pc->tries = 0;
+        return;
+    }
+
+    if (state & NGX_PEER_FAILED) {
+        now = ngx_time();
+
+        peer = &rrp->peers->peer[rrp->current];
+
+        /* ngx_lock_mutex(rrp->peers->mutex); */
+
+        peer->fails++;
+        peer->accessed = now;
+
+        if (peer->current_weight > 1) {
+            peer->current_weight /= 2;
+        }
+
+        /* ngx_unlock_mutex(rrp->peers->mutex); */
+    }
+
+    rrp->current++;
+
+    if (rrp->current >= rrp->peers->number) {
+        rrp->current = 0;
+    }
+
+    if (pc->tries) {
+        pc->tries--;
+    }
+
+    /* ngx_unlock_mutex(rrp->peers->mutex); */
+}
+
+
+#if (NGX_HTTP_SSL)
+
+void
+ngx_http_upstream_save_round_robin_peer(ngx_peer_connection_t *pc, void *data)
+{
+    ngx_http_upstream_rr_peer_data_t  *rrp = data;
+
+    ngx_ssl_session_t            *ssl_session;
+    ngx_http_upstream_rr_peer_t  *peer;
+
+    ssl_session = ngx_ssl_get_session(pc->connection);
+
+    if (ssl_session == NULL) {
+        return;
+    }
+
+    peer = &rrp->peers->peer[rrp->current];
+
+    /* ngx_lock_mutex(rrp->peers->mutex); */
+    peer->ssl_session = ssl_session;
+    /* ngx_unlock_mutex(rrp->peers->mutex); */
+
+    if (pc->ssl_session) {
+        /* TODO: may block */
+        ngx_ssl_free_session(pc->ssl_session);
+    }
+}
+
+#endif