diff -burN nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_hash_module.c nginx-1.12.1/src/http/modules/ngx_http_upstream_hash_module.c
--- nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_hash_module.c	2017-07-11 13:24:08.000000000 +0000
+++ nginx-1.12.1/src/http/modules/ngx_http_upstream_hash_module.c	2017-07-13 17:58:44.687213233 +0000
@@ -9,6 +9,9 @@
 #include <ngx_core.h>
 #include <ngx_http.h>
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+#include "ngx_http_upstream_check_module.h"
+#endif
 
 typedef struct {
     uint32_t                            hash;
@@ -235,6 +238,14 @@
             goto next;
         }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                       "get hash peer, check_index: %ui", peer->check_index);
+        if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+            goto next;
+        }
+#endif
+
         if (peer->max_fails
             && peer->fails >= peer->max_fails
             && now - peer->checked <= peer->fail_timeout)
@@ -538,6 +549,15 @@
                 continue;
             }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                           "get consistent_hash peer, check_index: %ui",
+                           peer->check_index);
+            if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+                continue;
+            }
+#endif
+
             if (peer->server.len != server->len
                 || ngx_strncmp(peer->server.data, server->data, server->len)
                    != 0)
diff -burN nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_ip_hash_module.c nginx-1.12.1/src/http/modules/ngx_http_upstream_ip_hash_module.c
--- nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_ip_hash_module.c	2017-07-11 13:24:08.000000000 +0000
+++ nginx-1.12.1/src/http/modules/ngx_http_upstream_ip_hash_module.c	2017-07-13 17:59:48.205692500 +0000
@@ -9,6 +9,9 @@
 #include <ngx_core.h>
 #include <ngx_http.h>
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+#include "ngx_http_upstream_check_module.h"
+#endif
 
 typedef struct {
     /* the round robin data must be first */
@@ -205,6 +208,15 @@
             goto next;
         }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+            "get ip_hash peer, check_index: %ui",
+             peer->check_index);
+        if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+            goto next;
+        }
+#endif
+
         if (peer->max_fails
             && peer->fails >= peer->max_fails
             && now - peer->checked <= peer->fail_timeout)
diff -burN nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_least_conn_module.c nginx-1.12.1/src/http/modules/ngx_http_upstream_least_conn_module.c
--- nginx-1.12.1_orig/src/http/modules/ngx_http_upstream_least_conn_module.c	2017-07-11 13:24:08.000000000 +0000
+++ nginx-1.12.1/src/http/modules/ngx_http_upstream_least_conn_module.c	2017-07-13 18:05:34.417398156 +0000
@@ -9,6 +9,10 @@
 #include <ngx_core.h>
 #include <ngx_http.h>
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+#include "ngx_http_upstream_check_module.h"
+#endif
+
 
 static ngx_int_t ngx_http_upstream_init_least_conn_peer(ngx_http_request_t *r,
     ngx_http_upstream_srv_conf_t *us);
@@ -147,6 +151,16 @@
             continue;
         }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                "get least_conn peer, check_index: %ui",
+                peer->check_index);
+
+        if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+            continue;
+        }
+#endif
+
         if (peer->max_fails
             && peer->fails >= peer->max_fails
             && now - peer->checked <= peer->fail_timeout)
@@ -202,6 +216,16 @@
                 continue;
             }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                    "get least_conn peer, check_index: %ui",
+                    peer->check_index);
+
+            if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+                continue;
+            }
+#endif
+
             if (peer->conns * best->weight != best->conns * peer->weight) {
                 continue;
             }
diff -burN nginx-1.12.1_orig/src/http/ngx_http_upstream_round_robin.c nginx-1.12.1/src/http/ngx_http_upstream_round_robin.c
--- nginx-1.12.1_orig/src/http/ngx_http_upstream_round_robin.c	2017-07-11 13:24:09.000000000 +0000
+++ nginx-1.12.1/src/http/ngx_http_upstream_round_robin.c	2017-07-13 18:13:00.510764315 +0000
@@ -9,6 +9,10 @@
 #include <ngx_core.h>
 #include <ngx_http.h>
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+#include "ngx_http_upstream_check_module.h"
+#endif
+
 
 #define ngx_http_upstream_tries(p) ((p)->number                               \
                                     + ((p)->next ? (p)->next->number : 0))
@@ -98,6 +102,15 @@
                 peer[n].down = server[i].down;
                 peer[n].server = server[i].name;
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+                if (!server[i].down) {
+                    peer[n].check_index =
+                        ngx_http_upstream_check_add_peer(cf, us, &server[i].addrs[j]);
+                } else {
+                    peer[n].check_index = (ngx_uint_t) NGX_ERROR;
+                }
+#endif
+
                 *peerp = &peer[n];
                 peerp = &peer[n].next;
                 n++;
@@ -162,6 +175,16 @@
                 peer[n].down = server[i].down;
                 peer[n].server = server[i].name;
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+                if (!server[i].down) {
+                    peer[n].check_index =
+                        ngx_http_upstream_check_add_peer(cf, us, &server[i].addrs[j]);
+                }
+                else {
+                    peer[n].check_index = (ngx_uint_t) NGX_ERROR;
+                }
+#endif
+
                 *peerp = &peer[n];
                 peerp = &peer[n].next;
                 n++;
@@ -228,6 +251,9 @@
         peer[i].max_conns = 0;
         peer[i].max_fails = 1;
         peer[i].fail_timeout = 10;
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        peer[i].check_index = (ngx_uint_t) NGX_ERROR;
+#endif
         *peerp = &peer[i];
         peerp = &peer[i].next;
     }
@@ -344,6 +370,9 @@
         peer[0].max_conns = 0;
         peer[0].max_fails = 1;
         peer[0].fail_timeout = 10;
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        peer[0].check_index = (ngx_uint_t) NGX_ERROR;
+#endif
         peers->peer = peer;
 
     } else {
@@ -378,6 +407,9 @@
             peer[i].max_conns = 0;
             peer[i].max_fails = 1;
             peer[i].fail_timeout = 10;
+#if (NGX_HTTP_UPSTREAM_CHECK)
+            peer[i].check_index = (ngx_uint_t) NGX_ERROR;
+#endif
             *peerp = &peer[i];
             peerp = &peer[i].next;
         }
@@ -443,6 +475,12 @@
             goto failed;
         }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+            goto failed;
+        }
+#endif
+
         rrp->current = peer;
 
     } else {
@@ -537,6 +575,12 @@
             continue;
         }
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+        if (ngx_http_upstream_check_peer_down(peer->check_index)) {
+            continue;
+        }
+#endif
+
         if (peer->max_fails
             && peer->fails >= peer->max_fails
             && now - peer->checked <= peer->fail_timeout)
diff -burN nginx-1.12.1_orig/src/http/ngx_http_upstream_round_robin.h nginx-1.12.1/src/http/ngx_http_upstream_round_robin.h
--- nginx-1.12.1_orig/src/http/ngx_http_upstream_round_robin.h	2017-07-11 13:24:09.000000000 +0000
+++ nginx-1.12.1/src/http/ngx_http_upstream_round_robin.h	2017-07-13 18:13:30.254055435 +0000
@@ -38,6 +38,10 @@
     ngx_msec_t                      slow_start;
     ngx_msec_t                      start_time;
 
+#if (NGX_HTTP_UPSTREAM_CHECK)
+    ngx_uint_t                      check_index;
+#endif
+
     ngx_uint_t                      down;
 
 #if (NGX_HTTP_SSL || NGX_COMPAT)