new file mode 100644
--- /dev/null
+++ b/src/stream/ngx_stream_upstream_round_robin.c
@@ -0,0 +1,697 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ * Copyright (C) Nginx, Inc.
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_stream.h>
+
+
+#define ngx_stream_upstream_tries(p) ((p)->number                             \
+                                      + ((p)->next ? (p)->next->number : 0))
+
+
+static ngx_stream_upstream_rr_peer_t *ngx_stream_upstream_get_peer(
+    ngx_stream_upstream_rr_peer_data_t *rrp);
+
+#if (NGX_STREAM_SSL)
+
+static ngx_int_t ngx_stream_upstream_set_round_robin_peer_session(
+    ngx_peer_connection_t *pc, void *data);
+static void ngx_stream_upstream_save_round_robin_peer_session(
+    ngx_peer_connection_t *pc, void *data);
+
+#endif
+
+
+ngx_int_t
+ngx_stream_upstream_init_round_robin(ngx_conf_t *cf,
+    ngx_stream_upstream_srv_conf_t *us)
+{
+    ngx_url_t                        u;
+    ngx_uint_t                       i, j, n, w;
+    ngx_stream_upstream_server_t    *server;
+    ngx_stream_upstream_rr_peer_t   *peer, **peerp;
+    ngx_stream_upstream_rr_peers_t  *peers, *backup;
+
+    us->peer.init = ngx_stream_upstream_init_round_robin_peer;
+
+    if (us->servers) {
+        server = us->servers->elts;
+
+        n = 0;
+        w = 0;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            if (server[i].backup) {
+                continue;
+            }
+
+            n += server[i].naddrs;
+            w += server[i].naddrs * server[i].weight;
+        }
+
+        if (n == 0) {
+            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                          "no servers in upstream \"%V\" in %s:%ui",
+                          &us->host, us->file_name, us->line);
+            return NGX_ERROR;
+        }
+
+        peers = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peers_t));
+        if (peers == NULL) {
+            return NGX_ERROR;
+        }
+
+        peer = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peer_t) * n);
+        if (peer == NULL) {
+            return NGX_ERROR;
+        }
+
+        peers->single = (n == 1);
+        peers->number = n;
+        peers->weighted = (w != n);
+        peers->total_weight = w;
+        peers->name = &us->host;
+
+        n = 0;
+        peerp = &peers->peer;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            if (server[i].backup) {
+                continue;
+            }
+
+            for (j = 0; j < server[i].naddrs; j++) {
+                peer[n].sockaddr = server[i].addrs[j].sockaddr;
+                peer[n].socklen = server[i].addrs[j].socklen;
+                peer[n].name = server[i].addrs[j].name;
+                peer[n].weight = server[i].weight;
+                peer[n].effective_weight = server[i].weight;
+                peer[n].current_weight = 0;
+                peer[n].max_fails = server[i].max_fails;
+                peer[n].fail_timeout = server[i].fail_timeout;
+                peer[n].down = server[i].down;
+                peer[n].server = server[i].name;
+
+                *peerp = &peer[n];
+                peerp = &peer[n].next;
+                n++;
+            }
+        }
+
+        us->peer.data = peers;
+
+        /* backup servers */
+
+        n = 0;
+        w = 0;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            if (!server[i].backup) {
+                continue;
+            }
+
+            n += server[i].naddrs;
+            w += server[i].naddrs * server[i].weight;
+        }
+
+        if (n == 0) {
+            return NGX_OK;
+        }
+
+        backup = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peers_t));
+        if (backup == NULL) {
+            return NGX_ERROR;
+        }
+
+        peer = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peer_t) * n);
+        if (peer == NULL) {
+            return NGX_ERROR;
+        }
+
+        peers->single = 0;
+        backup->single = 0;
+        backup->number = n;
+        backup->weighted = (w != n);
+        backup->total_weight = w;
+        backup->name = &us->host;
+
+        n = 0;
+        peerp = &backup->peer;
+
+        for (i = 0; i < us->servers->nelts; i++) {
+            if (!server[i].backup) {
+                continue;
+            }
+
+            for (j = 0; j < server[i].naddrs; j++) {
+                peer[n].sockaddr = server[i].addrs[j].sockaddr;
+                peer[n].socklen = server[i].addrs[j].socklen;
+                peer[n].name = server[i].addrs[j].name;
+                peer[n].weight = server[i].weight;
+                peer[n].effective_weight = server[i].weight;
+                peer[n].current_weight = 0;
+                peer[n].max_fails = server[i].max_fails;
+                peer[n].fail_timeout = server[i].fail_timeout;
+                peer[n].down = server[i].down;
+                peer[n].server = server[i].name;
+
+                *peerp = &peer[n];
+                peerp = &peer[n].next;
+                n++;
+            }
+        }
+
+        peers->next = backup;
+
+        return NGX_OK;
+    }
+
+
+    /* an upstream implicitly defined by proxy_pass, etc. */
+
+    if (us->port == 0) {
+        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                      "no port in upstream \"%V\" in %s:%ui",
+                      &us->host, us->file_name, us->line);
+        return NGX_ERROR;
+    }
+
+    ngx_memzero(&u, sizeof(ngx_url_t));
+
+    u.host = us->host;
+    u.port = us->port;
+
+    if (ngx_inet_resolve_host(cf->pool, &u) != NGX_OK) {
+        if (u.err) {
+            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                          "%s in upstream \"%V\" in %s:%ui",
+                          u.err, &us->host, us->file_name, us->line);
+        }
+
+        return NGX_ERROR;
+    }
+
+    n = u.naddrs;
+
+    peers = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peers_t));
+    if (peers == NULL) {
+        return NGX_ERROR;
+    }
+
+    peer = ngx_pcalloc(cf->pool, sizeof(ngx_stream_upstream_rr_peer_t) * n);
+    if (peer == NULL) {
+        return NGX_ERROR;
+    }
+
+    peers->single = (n == 1);
+    peers->number = n;
+    peers->weighted = 0;
+    peers->total_weight = n;
+    peers->name = &us->host;
+
+    peerp = &peers->peer;
+
+    for (i = 0; i < u.naddrs; i++) {
+        peer[i].sockaddr = u.addrs[i].sockaddr;
+        peer[i].socklen = u.addrs[i].socklen;
+        peer[i].name = u.addrs[i].name;
+        peer[i].weight = 1;
+        peer[i].effective_weight = 1;
+        peer[i].current_weight = 0;
+        peer[i].max_fails = 1;
+        peer[i].fail_timeout = 10;
+        *peerp = &peer[i];
+        peerp = &peer[i].next;
+    }
+
+    us->peer.data = peers;
+
+    /* implicitly defined upstream has no backup servers */
+
+    return NGX_OK;
+}
+
+
+ngx_int_t
+ngx_stream_upstream_init_round_robin_peer(ngx_stream_session_t *s,
+    ngx_stream_upstream_srv_conf_t *us)
+{
+    ngx_uint_t                           n;
+    ngx_stream_upstream_rr_peer_data_t  *rrp;
+
+    rrp = s->upstream->peer.data;
+
+    if (rrp == NULL) {
+        rrp = ngx_palloc(s->connection->pool,
+                         sizeof(ngx_stream_upstream_rr_peer_data_t));
+        if (rrp == NULL) {
+            return NGX_ERROR;
+        }
+
+        s->upstream->peer.data = rrp;
+    }
+
+    rrp->peers = us->peer.data;
+    rrp->current = NULL;
+
+    n = rrp->peers->number;
+
+    if (rrp->peers->next && rrp->peers->next->number > n) {
+        n = rrp->peers->next->number;
+    }
+
+    if (n <= 8 * sizeof(uintptr_t)) {
+        rrp->tried = &rrp->data;
+        rrp->data = 0;
+
+    } else {
+        n = (n + (8 * sizeof(uintptr_t) - 1)) / (8 * sizeof(uintptr_t));
+
+        rrp->tried = ngx_pcalloc(s->connection->pool, n * sizeof(uintptr_t));
+        if (rrp->tried == NULL) {
+            return NGX_ERROR;
+        }
+    }
+
+    s->upstream->peer.get = ngx_stream_upstream_get_round_robin_peer;
+    s->upstream->peer.free = ngx_stream_upstream_free_round_robin_peer;
+    s->upstream->peer.tries = ngx_stream_upstream_tries(rrp->peers);
+#if (NGX_STREAM_SSL)
+    s->upstream->peer.set_session =
+                             ngx_stream_upstream_set_round_robin_peer_session;
+    s->upstream->peer.save_session =
+                             ngx_stream_upstream_save_round_robin_peer_session;
+#endif
+
+    return NGX_OK;
+}
+
+
+ngx_int_t
+ngx_stream_upstream_get_round_robin_peer(ngx_peer_connection_t *pc, void *data)
+{
+    ngx_stream_upstream_rr_peer_data_t *rrp = data;
+
+    ngx_int_t                        rc;
+    ngx_uint_t                       i, n;
+    ngx_stream_upstream_rr_peer_t   *peer;
+    ngx_stream_upstream_rr_peers_t  *peers;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                   "get rr peer, try: %ui", pc->tries);
+
+    pc->connection = NULL;
+
+    peers = rrp->peers;
+    ngx_stream_upstream_rr_peers_wlock(peers);
+
+    if (peers->single) {
+        peer = peers->peer;
+
+        if (peer->down) {
+            goto failed;
+        }
+
+        rrp->current = peer;
+
+    } else {
+
+        /* there are several peers */
+
+        peer = ngx_stream_upstream_get_peer(rrp);
+
+        if (peer == NULL) {
+            goto failed;
+        }
+
+        ngx_log_debug2(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                       "get rr peer, current: %p %i",
+                       peer, peer->current_weight);
+    }
+
+    pc->sockaddr = peer->sockaddr;
+    pc->socklen = peer->socklen;
+    pc->name = &peer->name;
+
+    peer->conns++;
+
+    ngx_stream_upstream_rr_peers_unlock(peers);
+
+    return NGX_OK;
+
+failed:
+
+    if (peers->next) {
+
+        ngx_log_debug0(NGX_LOG_DEBUG_STREAM, pc->log, 0, "backup servers");
+
+        rrp->peers = peers->next;
+
+        n = (rrp->peers->number + (8 * sizeof(uintptr_t) - 1))
+                / (8 * sizeof(uintptr_t));
+
+        for (i = 0; i < n; i++) {
+             rrp->tried[i] = 0;
+        }
+
+        ngx_stream_upstream_rr_peers_unlock(peers);
+
+        rc = ngx_stream_upstream_get_round_robin_peer(pc, rrp);
+
+        if (rc != NGX_BUSY) {
+            return rc;
+        }
+
+        ngx_stream_upstream_rr_peers_wlock(peers);
+    }
+
+    /* all peers failed, mark them as live for quick recovery */
+
+    for (peer = peers->peer; peer; peer = peer->next) {
+        peer->fails = 0;
+    }
+
+    ngx_stream_upstream_rr_peers_unlock(peers);
+
+    pc->name = peers->name;
+
+    return NGX_BUSY;
+}
+
+
+static ngx_stream_upstream_rr_peer_t *
+ngx_stream_upstream_get_peer(ngx_stream_upstream_rr_peer_data_t *rrp)
+{
+    time_t                          now;
+    uintptr_t                       m;
+    ngx_int_t                       total;
+    ngx_uint_t                      i, n, p;
+    ngx_stream_upstream_rr_peer_t  *peer, *best;
+
+    now = ngx_time();
+
+    best = NULL;
+    total = 0;
+
+#if (NGX_SUPPRESS_WARN)
+    p = 0;
+#endif
+
+    for (peer = rrp->peers->peer, i = 0;
+         peer;
+         peer = peer->next, i++)
+    {
+
+        n = i / (8 * sizeof(uintptr_t));
+        m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+        if (rrp->tried[n] & m) {
+            continue;
+        }
+
+        if (peer->down) {
+            continue;
+        }
+
+        if (peer->max_fails
+            && peer->fails >= peer->max_fails
+            && now - peer->checked <= peer->fail_timeout)
+        {
+            continue;
+        }
+
+        peer->current_weight += peer->effective_weight;
+        total += peer->effective_weight;
+
+        if (peer->effective_weight < peer->weight) {
+            peer->effective_weight++;
+        }
+
+        if (best == NULL || peer->current_weight > best->current_weight) {
+            best = peer;
+            p = i;
+        }
+    }
+
+    if (best == NULL) {
+        return NULL;
+    }
+
+    rrp->current = best;
+
+    n = p / (8 * sizeof(uintptr_t));
+    m = (uintptr_t) 1 << p % (8 * sizeof(uintptr_t));
+
+    rrp->tried[n] |= m;
+
+    best->current_weight -= total;
+
+    if (now - best->checked > best->fail_timeout) {
+        best->checked = now;
+    }
+
+    return best;
+}
+
+
+void
+ngx_stream_upstream_free_round_robin_peer(ngx_peer_connection_t *pc, void *data,
+    ngx_uint_t state)
+{
+    ngx_stream_upstream_rr_peer_data_t  *rrp = data;
+
+    time_t                          now;
+    ngx_stream_upstream_rr_peer_t  *peer;
+
+    ngx_log_debug2(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                   "free rr peer %ui %ui", pc->tries, state);
+
+    peer = rrp->current;
+
+    ngx_stream_upstream_rr_peers_rlock(rrp->peers);
+    ngx_stream_upstream_rr_peer_lock(rrp->peers, peer);
+
+    if (rrp->peers->single) {
+        peer->conns--;
+
+        ngx_stream_upstream_rr_peer_unlock(rrp->peers, peer);
+        ngx_stream_upstream_rr_peers_unlock(rrp->peers);
+
+        pc->tries = 0;
+        return;
+    }
+
+    if (state & NGX_PEER_FAILED) {
+        now = ngx_time();
+
+        peer->fails++;
+        peer->accessed = now;
+        peer->checked = now;
+
+        if (peer->max_fails) {
+            peer->effective_weight -= peer->weight / peer->max_fails;
+        }
+
+        ngx_log_debug2(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                       "free rr peer failed: %p %i",
+                       peer, peer->effective_weight);
+
+        if (peer->effective_weight < 0) {
+            peer->effective_weight = 0;
+        }
+
+    } else {
+
+        /* mark peer live if check passed */
+
+        if (peer->accessed < peer->checked) {
+            peer->fails = 0;
+        }
+    }
+
+    peer->conns--;
+
+    ngx_stream_upstream_rr_peer_unlock(rrp->peers, peer);
+    ngx_stream_upstream_rr_peers_unlock(rrp->peers);
+
+    if (pc->tries) {
+        pc->tries--;
+    }
+}
+
+
+#if (NGX_STREAM_SSL)
+
+static ngx_int_t
+ngx_stream_upstream_set_round_robin_peer_session(ngx_peer_connection_t *pc,
+    void *data)
+{
+    ngx_stream_upstream_rr_peer_data_t  *rrp = data;
+
+    ngx_int_t                        rc;
+    ngx_ssl_session_t               *ssl_session;
+    ngx_stream_upstream_rr_peer_t   *peer;
+#if (NGX_STREAM_UPSTREAM_ZONE)
+    int                              len;
+#if OPENSSL_VERSION_NUMBER >= 0x0090707fL
+    const
+#endif
+    u_char                          *p;
+    ngx_stream_upstream_rr_peers_t  *peers;
+    u_char                           buf[NGX_SSL_MAX_SESSION_SIZE];
+#endif
+
+    peer = rrp->current;
+
+#if (NGX_STREAM_UPSTREAM_ZONE)
+    peers = rrp->peers;
+
+    if (peers->shpool) {
+        ngx_stream_upstream_rr_peers_rlock(peers);
+        ngx_stream_upstream_rr_peer_lock(peers, peer);
+
+        if (peer->ssl_session == NULL) {
+            ngx_stream_upstream_rr_peer_unlock(peers, peer);
+            ngx_stream_upstream_rr_peers_unlock(peers);
+            return NGX_OK;
+        }
+
+        len = peer->ssl_session_len;
+
+        ngx_memcpy(buf, peer->ssl_session, len);
+
+        ngx_stream_upstream_rr_peer_unlock(peers, peer);
+        ngx_stream_upstream_rr_peers_unlock(peers);
+
+        p = buf;
+        ssl_session = d2i_SSL_SESSION(NULL, &p, len);
+
+        rc = ngx_ssl_set_session(pc->connection, ssl_session);
+
+        ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                       "set session: %p", ssl_session);
+
+        ngx_ssl_free_session(ssl_session);
+
+        return rc;
+    }
+#endif
+
+    ssl_session = peer->ssl_session;
+
+    rc = ngx_ssl_set_session(pc->connection, ssl_session);
+
+    ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                   "set session: %p", ssl_session);
+
+    return rc;
+}
+
+
+static void
+ngx_stream_upstream_save_round_robin_peer_session(ngx_peer_connection_t *pc,
+    void *data)
+{
+    ngx_stream_upstream_rr_peer_data_t  *rrp = data;
+
+    ngx_ssl_session_t               *old_ssl_session, *ssl_session;
+    ngx_stream_upstream_rr_peer_t   *peer;
+#if (NGX_STREAM_UPSTREAM_ZONE)
+    int                              len;
+    u_char                          *p;
+    ngx_stream_upstream_rr_peers_t  *peers;
+    u_char                           buf[NGX_SSL_MAX_SESSION_SIZE];
+#endif
+
+#if (NGX_STREAM_UPSTREAM_ZONE)
+    peers = rrp->peers;
+
+    if (peers->shpool) {
+
+        ssl_session = SSL_get0_session(pc->connection->ssl->connection);
+
+        if (ssl_session == NULL) {
+            return;
+        }
+
+        ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                       "save session: %p", ssl_session);
+
+        len = i2d_SSL_SESSION(ssl_session, NULL);
+
+        /* do not cache too big session */
+
+        if (len > NGX_SSL_MAX_SESSION_SIZE) {
+            return;
+        }
+
+        p = buf;
+        (void) i2d_SSL_SESSION(ssl_session, &p);
+
+        peer = rrp->current;
+
+        ngx_stream_upstream_rr_peers_rlock(peers);
+        ngx_stream_upstream_rr_peer_lock(peers, peer);
+
+        if (len > peer->ssl_session_len) {
+            ngx_shmtx_lock(&peers->shpool->mutex);
+
+            if (peer->ssl_session) {
+                ngx_slab_free_locked(peers->shpool, peer->ssl_session);
+            }
+
+            peer->ssl_session = ngx_slab_alloc_locked(peers->shpool, len);
+
+            ngx_shmtx_unlock(&peers->shpool->mutex);
+
+            if (peer->ssl_session == NULL) {
+                peer->ssl_session_len = 0;
+
+                ngx_stream_upstream_rr_peer_unlock(peers, peer);
+                ngx_stream_upstream_rr_peers_unlock(peers);
+                return;
+            }
+
+            peer->ssl_session_len = len;
+        }
+
+        ngx_memcpy(peer->ssl_session, buf, len);
+
+        ngx_stream_upstream_rr_peer_unlock(peers, peer);
+        ngx_stream_upstream_rr_peers_unlock(peers);
+
+        return;
+    }
+#endif
+
+    ssl_session = ngx_ssl_get_session(pc->connection);
+
+    if (ssl_session == NULL) {
+        return;
+    }
+
+    ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                   "save session: %p", ssl_session);
+
+    peer = rrp->current;
+
+    old_ssl_session = peer->ssl_session;
+    peer->ssl_session = ssl_session;
+
+    if (old_ssl_session) {
+
+        ngx_log_debug1(NGX_LOG_DEBUG_STREAM, pc->log, 0,
+                       "old session: %p", old_ssl_session);
+
+        /* TODO: may block */
+
+        ngx_ssl_free_session(old_ssl_session);
+    }
+}
+
+#endif