new file mode 100644
--- /dev/null
+++ b/src/http/modules/ngx_http_upstream_hash_module.c
@@ -0,0 +1,631 @@
+
+/*
+ * Copyright (C) Roman Arutyunyan
+ * Copyright (C) Nginx, Inc.
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    uint32_t                            hash;
+    ngx_str_t                          *server;
+} ngx_http_upstream_chash_point_t;
+
+
+typedef struct {
+    ngx_uint_t                          number;
+    ngx_http_upstream_chash_point_t     point[1];
+} ngx_http_upstream_chash_points_t;
+
+
+typedef struct {
+    ngx_http_complex_value_t            key;
+    ngx_http_upstream_chash_points_t   *points;
+} ngx_http_upstream_hash_srv_conf_t;
+
+
+typedef struct {
+    /* the round robin data must be first */
+    ngx_http_upstream_rr_peer_data_t    rrp;
+    ngx_http_upstream_hash_srv_conf_t  *conf;
+    ngx_str_t                           key;
+    ngx_uint_t                          tries;
+    ngx_uint_t                          rehash;
+    uint32_t                            hash;
+    ngx_event_get_peer_pt               get_rr_peer;
+} ngx_http_upstream_hash_peer_data_t;
+
+
+static ngx_int_t ngx_http_upstream_init_hash(ngx_conf_t *cf,
+    ngx_http_upstream_srv_conf_t *us);
+static ngx_int_t ngx_http_upstream_init_hash_peer(ngx_http_request_t *r,
+    ngx_http_upstream_srv_conf_t *us);
+static ngx_int_t ngx_http_upstream_get_hash_peer(ngx_peer_connection_t *pc,
+    void *data);
+
+static ngx_int_t ngx_http_upstream_init_chash(ngx_conf_t *cf,
+    ngx_http_upstream_srv_conf_t *us);
+static void ngx_http_upstream_add_chash_point(
+    ngx_http_upstream_chash_points_t *points, uint32_t hash, ngx_str_t *server);
+static ngx_uint_t ngx_http_upstream_find_chash_point(
+    ngx_http_upstream_chash_points_t *points, uint32_t hash);
+static ngx_int_t ngx_http_upstream_init_chash_peer(ngx_http_request_t *r,
+    ngx_http_upstream_srv_conf_t *us);
+static ngx_int_t ngx_http_upstream_get_chash_peer(ngx_peer_connection_t *pc,
+    void *data);
+
+static void *ngx_http_upstream_hash_create_conf(ngx_conf_t *cf);
+static char *ngx_http_upstream_hash(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+
+
+static ngx_command_t  ngx_http_upstream_hash_commands[] = {
+
+    { ngx_string("hash"),
+      NGX_HTTP_UPS_CONF|NGX_CONF_TAKE12,
+      ngx_http_upstream_hash,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      0,
+      NULL },
+
+      ngx_null_command
+};
+
+
+static ngx_http_module_t  ngx_http_upstream_hash_module_ctx = {
+    NULL,                                  /* preconfiguration */
+    NULL,                                  /* postconfiguration */
+
+    NULL,                                  /* create main configuration */
+    NULL,                                  /* init main configuration */
+
+    ngx_http_upstream_hash_create_conf,    /* create server configuration */
+    NULL,                                  /* merge server configuration */
+
+    NULL,                                  /* create location configuration */
+    NULL                                   /* merge location configuration */
+};
+
+
+ngx_module_t  ngx_http_upstream_hash_module = {
+    NGX_MODULE_V1,
+    &ngx_http_upstream_hash_module_ctx,    /* module context */
+    ngx_http_upstream_hash_commands,       /* module directives */
+    NGX_HTTP_MODULE,                       /* module type */
+    NULL,                                  /* init master */
+    NULL,                                  /* init module */
+    NULL,                                  /* init process */
+    NULL,                                  /* init thread */
+    NULL,                                  /* exit thread */
+    NULL,                                  /* exit process */
+    NULL,                                  /* exit master */
+    NGX_MODULE_V1_PADDING
+};
+
+
+static ngx_int_t
+ngx_http_upstream_init_hash(ngx_conf_t *cf, ngx_http_upstream_srv_conf_t *us)
+{
+    if (ngx_http_upstream_init_round_robin(cf, us) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    us->peer.init = ngx_http_upstream_init_hash_peer;
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_upstream_init_hash_peer(ngx_http_request_t *r,
+    ngx_http_upstream_srv_conf_t *us)
+{
+    ngx_http_upstream_hash_srv_conf_t   *hcf;
+    ngx_http_upstream_hash_peer_data_t  *hp;
+
+    hp = ngx_palloc(r->pool, sizeof(ngx_http_upstream_hash_peer_data_t));
+    if (hp == NULL) {
+        return NGX_ERROR;
+    }
+
+    r->upstream->peer.data = &hp->rrp;
+
+    if (ngx_http_upstream_init_round_robin_peer(r, us) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    r->upstream->peer.get = ngx_http_upstream_get_hash_peer;
+
+    hcf = ngx_http_conf_upstream_srv_conf(us, ngx_http_upstream_hash_module);
+
+    if (ngx_http_complex_value(r, &hcf->key, &hp->key) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "upstream hash key:\"%V\"", &hp->key);
+
+    hp->conf = hcf;
+    hp->tries = 0;
+    hp->rehash = 0;
+    hp->hash = 0;
+    hp->get_rr_peer = ngx_http_upstream_get_round_robin_peer;
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_upstream_get_hash_peer(ngx_peer_connection_t *pc, void *data)
+{
+    ngx_http_upstream_hash_peer_data_t  *hp = data;
+
+    time_t                        now;
+    u_char                        buf[NGX_INT_T_LEN];
+    size_t                        size;
+    uint32_t                      hash;
+    ngx_int_t                     w;
+    uintptr_t                     m;
+    ngx_uint_t                    i, n, p;
+    ngx_http_upstream_rr_peer_t  *peer;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                   "get hash peer, try: %ui", pc->tries);
+
+    if (hp->tries > 20 || hp->rrp.peers->single) {
+        return hp->get_rr_peer(pc, &hp->rrp);
+    }
+
+    now = ngx_time();
+
+    pc->cached = 0;
+    pc->connection = NULL;
+
+    for ( ;; ) {
+
+        /*
+         * Hash expression is compatible with Cache::Memcached:
+         * ((crc32([REHASH] KEY) >> 16) & 0x7fff) + PREV_HASH
+         * with REHASH omitted at the first iteration.
+         */
+
+        ngx_crc32_init(hash);
+
+        if (hp->rehash > 0) {
+            size = ngx_sprintf(buf, "%ui", hp->rehash) - buf;
+            ngx_crc32_update(&hash, buf, size);
+        }
+
+        ngx_crc32_update(&hash, hp->key.data, hp->key.len);
+        ngx_crc32_final(hash);
+
+        hash = (hash >> 16) & 0x7fff;
+
+        hp->hash += hash;
+        hp->rehash++;
+
+        if (!hp->rrp.peers->weighted) {
+            p = hp->hash % hp->rrp.peers->number;
+
+        } else {
+            w = hp->hash % hp->rrp.peers->total_weight;
+
+            for (i = 0; i < hp->rrp.peers->number; i++) {
+                w -= hp->rrp.peers->peer[i].weight;
+                if (w < 0) {
+                    break;
+                }
+            }
+
+            p = i;
+        }
+
+        n = p / (8 * sizeof(uintptr_t));
+        m = (uintptr_t) 1 << p % (8 * sizeof(uintptr_t));
+
+        if (hp->rrp.tried[n] & m) {
+            goto next;
+        }
+
+        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                       "get hash peer, value:%uD, peer:%ui", hp->hash, p);
+
+        peer = &hp->rrp.peers->peer[p];
+
+        if (peer->down) {
+            goto next;
+        }
+
+        if (peer->max_fails
+            && peer->fails >= peer->max_fails
+            && now - peer->checked <= peer->fail_timeout)
+        {
+            goto next;
+        }
+
+        break;
+
+    next:
+
+        if (++hp->tries > 20) {
+            return hp->get_rr_peer(pc, &hp->rrp);
+        }
+    }
+
+    hp->rrp.current = p;
+
+    pc->sockaddr = peer->sockaddr;
+    pc->socklen = peer->socklen;
+    pc->name = &peer->name;
+
+    if (now - peer->checked > peer->fail_timeout) {
+        peer->checked = now;
+    }
+
+    hp->rrp.tried[n] |= m;
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_upstream_init_chash(ngx_conf_t *cf, ngx_http_upstream_srv_conf_t *us)
+{
+    u_char                             *host, *port, c;
+    size_t                              host_len, port_len, size;
+    uint32_t                            hash, base_hash, prev_hash;
+    ngx_str_t                          *server;
+    ngx_uint_t                          npoints, i, j;
+    ngx_http_upstream_rr_peer_t        *peer;
+    ngx_http_upstream_rr_peers_t       *peers;
+    ngx_http_upstream_chash_points_t   *points;
+    ngx_http_upstream_hash_srv_conf_t  *hcf;
+
+    if (ngx_http_upstream_init_round_robin(cf, us) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    us->peer.init = ngx_http_upstream_init_chash_peer;
+
+    peers = us->peer.data;
+    npoints = peers->total_weight * 160;
+
+    size = sizeof(ngx_http_upstream_chash_points_t)
+           + sizeof(ngx_http_upstream_chash_point_t) * (npoints - 1);
+
+    points = ngx_palloc(cf->pool, size);
+    if (points == NULL) {
+        return NGX_ERROR;
+    }
+
+    points->number = 0;
+
+    for (i = 0; i < peers->number; i++) {
+        peer = &peers->peer[i];
+        server = &peer->server;
+
+        /*
+         * Hash expression is compatible with Cache::Memcached::Fast:
+         * crc32(HOST \0 PORT PREV_HASH).
+         */
+
+        if (server->len >= 5
+            && ngx_strncasecmp(server->data, (u_char *) "unix:", 5) == 0)
+        {
+            host = server->data + 5;
+            host_len = server->len - 5;
+            port = NULL;
+            port_len = 0;
+            goto done;
+        }
+
+        for (j = 0; j < server->len; j++) {
+            c = server->data[server->len - j - 1];
+
+            if (c == ':') {
+                host = server->data;
+                host_len = server->len - j - 1;
+                port = server->data + server->len - j;
+                port_len = j;
+                goto done;
+            }
+
+            if (c < '0' || c > '9') {
+                break;
+            }
+        }
+
+        host = server->data;
+        host_len = server->len;
+        port = NULL;
+        port_len = 0;
+
+    done:
+
+        ngx_crc32_init(base_hash);
+        ngx_crc32_update(&base_hash, host, host_len);
+        ngx_crc32_update(&base_hash, (u_char *) "", 1);
+        ngx_crc32_update(&base_hash, port, port_len);
+
+        prev_hash = 0;
+        npoints = peer->weight * 160;
+
+        for (j = 0; j < npoints; j++) {
+            hash = base_hash;
+
+            ngx_crc32_update(&hash, (u_char *) &prev_hash, sizeof(uint32_t));
+            ngx_crc32_final(hash);
+
+            ngx_http_upstream_add_chash_point(points, hash, &peer->server);
+
+            prev_hash = hash;
+        }
+    }
+
+    hcf = ngx_http_conf_upstream_srv_conf(us, ngx_http_upstream_hash_module);
+    hcf->points = points;
+
+    return NGX_OK;
+}
+
+
+static void
+ngx_http_upstream_add_chash_point(ngx_http_upstream_chash_points_t *points,
+    uint32_t hash, ngx_str_t *server)
+{
+    size_t                            size;
+    ngx_uint_t                        i;
+    ngx_http_upstream_chash_point_t  *point;
+
+    i = ngx_http_upstream_find_chash_point(points, hash);
+    point = &points->point[i];
+
+    if (point->hash == hash) {
+        return;
+    }
+
+    size = (points->number - i) * sizeof(ngx_http_upstream_chash_point_t);
+
+    ngx_memmove(point + 1, point, size);
+
+    points->number++;
+    point->hash = hash;
+    point->server = server;
+}
+
+
+static ngx_uint_t
+ngx_http_upstream_find_chash_point(ngx_http_upstream_chash_points_t *points,
+    uint32_t hash)
+{
+    ngx_uint_t                        i, j, k;
+    ngx_http_upstream_chash_point_t  *point;
+
+    /* find first point >= hash */
+
+    point = &points->point[0];
+
+    i = 0;
+    j = points->number;
+
+    while (i < j) {
+        k = (i + j) / 2;
+
+        if (hash > point[k].hash) {
+            i = k + 1;
+
+        } else if (hash < point[k].hash) {
+            j = k;
+
+        } else {
+            return k;
+        }
+    }
+
+    return i;
+}
+
+
+static ngx_int_t
+ngx_http_upstream_init_chash_peer(ngx_http_request_t *r,
+    ngx_http_upstream_srv_conf_t *us)
+{
+    uint32_t                             hash;
+    ngx_http_upstream_hash_srv_conf_t   *hcf;
+    ngx_http_upstream_hash_peer_data_t  *hp;
+
+    if (ngx_http_upstream_init_hash_peer(r, us) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    r->upstream->peer.get = ngx_http_upstream_get_chash_peer;
+
+    hp = r->upstream->peer.data;
+    hcf = ngx_http_conf_upstream_srv_conf(us, ngx_http_upstream_hash_module);
+
+    hash = ngx_crc32_long(hp->key.data, hp->key.len);
+    hp->hash = ngx_http_upstream_find_chash_point(hcf->points, hash);
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_upstream_get_chash_peer(ngx_peer_connection_t *pc, void *data)
+{
+    ngx_http_upstream_hash_peer_data_t  *hp = data;
+
+    time_t                              now;
+    intptr_t                            m;
+    ngx_str_t                          *server;
+    ngx_int_t                           total;
+    ngx_uint_t                          i, n;
+    ngx_http_upstream_rr_peer_t        *peer, *best;
+    ngx_http_upstream_chash_point_t    *point;
+    ngx_http_upstream_chash_points_t   *points;
+    ngx_http_upstream_hash_srv_conf_t  *hcf;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                   "get consistent hash peer, try: %ui", pc->tries);
+
+    pc->cached = 0;
+    pc->connection = NULL;
+
+    now = ngx_time();
+    hcf = hp->conf;
+
+    points = hcf->points;
+    point = &points->point[0];
+
+    for ( ;; ) {
+        server = point[hp->hash % points->number].server;
+
+        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                       "consistent hash peer:%uD, server:\"%V\"",
+                       hp->hash, server);
+
+        best = NULL;
+        total = 0;
+
+        for (i = 0; i < hp->rrp.peers->number; i++) {
+
+            n = i / (8 * sizeof(uintptr_t));
+            m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+            if (hp->rrp.tried[n] & m) {
+                continue;
+            }
+
+            peer = &hp->rrp.peers->peer[i];
+
+            if (peer->down) {
+                continue;
+            }
+
+            if (peer->server.len != server->len
+                || ngx_strncmp(peer->server.data, server->data, server->len)
+                   != 0)
+            {
+                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;
+            }
+        }
+
+        if (best) {
+            best->current_weight -= total;
+
+            i = best - &hp->rrp.peers->peer[0];
+
+            hp->rrp.current = i;
+
+            n = i / (8 * sizeof(uintptr_t));
+            m = (uintptr_t) 1 << i % (8 * sizeof(uintptr_t));
+
+            hp->rrp.tried[n] |= m;
+
+            if (now - best->checked > best->fail_timeout) {
+                best->checked = now;
+            }
+
+            pc->sockaddr = best->sockaddr;
+            pc->socklen = best->socklen;
+            pc->name = &best->name;
+
+            return NGX_OK;
+        }
+
+        hp->hash++;
+        hp->tries++;
+
+        if (hp->tries >= points->number) {
+            return NGX_BUSY;
+        }
+    }
+}
+
+
+static void *
+ngx_http_upstream_hash_create_conf(ngx_conf_t *cf)
+{
+    ngx_http_upstream_hash_srv_conf_t  *conf;
+
+    conf = ngx_palloc(cf->pool, sizeof(ngx_http_upstream_hash_srv_conf_t));
+    if (conf == NULL) {
+        return NULL;
+    }
+
+    conf->points = NULL;
+
+    return conf;
+}
+
+
+static char *
+ngx_http_upstream_hash(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_upstream_hash_srv_conf_t  *hcf = conf;
+
+    ngx_str_t                         *value;
+    ngx_http_upstream_srv_conf_t      *uscf;
+    ngx_http_compile_complex_value_t   ccv;
+
+    value = cf->args->elts;
+
+    ngx_memzero(&ccv, sizeof(ngx_http_compile_complex_value_t));
+
+    ccv.cf = cf;
+    ccv.value = &value[1];
+    ccv.complex_value = &hcf->key;
+
+    if (ngx_http_compile_complex_value(&ccv) != NGX_OK) {
+        return NGX_CONF_ERROR;
+    }
+
+    uscf = ngx_http_conf_get_module_srv_conf(cf, ngx_http_upstream_module);
+
+    if (uscf->peer.init_upstream) {
+        ngx_conf_log_error(NGX_LOG_WARN, cf, 0,
+                           "load balancing method redefined");
+    }
+
+    uscf->flags = NGX_HTTP_UPSTREAM_CREATE
+                  |NGX_HTTP_UPSTREAM_WEIGHT
+                  |NGX_HTTP_UPSTREAM_MAX_FAILS
+                  |NGX_HTTP_UPSTREAM_FAIL_TIMEOUT
+                  |NGX_HTTP_UPSTREAM_DOWN;
+
+    if (cf->args->nelts == 2) {
+        uscf->peer.init_upstream = ngx_http_upstream_init_hash;
+
+    } else if (ngx_strcmp(value[2].data, "consistent") == 0) {
+        uscf->peer.init_upstream = ngx_http_upstream_init_chash;
+
+    } else {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                           "invalid parameter \"%V\"", &value[2]);
+        return NGX_CONF_ERROR;
+    }
+
+    return NGX_CONF_OK;
+}