Add proactive health check for the upstream servers.

This module is not built by default before Tengine-1.4.0,

it should be enabled with the --with-http_upstream_check_module configuration parameter.


http {
upstream cluster1 {
# simple round-robin
check interval=3000 rise=2 fall=5 timeout=1000 type=http;
check_http_send "HEAD / HTTP/1.0\r\n\r\n";
check_http_expect_alive http_2xx http_3xx;
upstream cluster2 {
# simple round-robin
check interval=3000 rise=2 fall=5 timeout=1000 type=http;
check_keepalive_requests 100;
check_http_send "HEAD / HTTP/1.1\r\nConnection: keep-alive\r\n\r\n";
check_http_expect_alive http_2xx http_3xx;
server {
listen 80;
location /1 {
proxy_pass http://cluster1;
location /2 {
proxy_pass http://cluster2;
location /status {
access_log off;
deny all;


Syntax: check interval=milliseconds [fall=count] [rise=count] [timeout=milliseconds] [default_down=true|false] [type=tcp|http|ssl_hello|mysql|ajp] [port=check_port]
Default: If the parameters are omitted, default values are: interval=30000 fall=5 rise=2 timeout=1000 default_down=true type=tcp>
Context: upstream

Add health check for the upstream servers.

The parameters' meanings are:

  • interval: the check request's interval time.
  • fall(fall_count): After fall_count failure checks, the server is marked down.
  • rise(rise_count): After rise_count successful checks, the server is marked up.
  • timeout: the check request's timeout.
  • default_down: specify initial state of backend server, default is down.
  • type: the check protocol type:

  • tcp: a simple TCP socket connect and peek one byte.

  • ssl_hello: send a client SSL hello packet and receive the server SSL hello packet.
  • http: send a http request packet, receive and parse the http response to diagnose if the upstream server is alive.
  • mysql: connect to the mysql server, receive the greeting response to diagnose if the upstream server is alive.
  • ajp: send an AJP Cping packet, receive and parse the AJP Cpong response to diagnose if the upstream server is alive.
  • port: specify the check port in the backend servers. It can be different with the original servers port. Default the port is 0 and it means the same as the original backend server. This option is added after tengine-1.4.0.

Syntax: check_keepalive_requests request_num
Default: 1
Context: upstream

The directive specifies the number of requests sent on a connection, the default vaule 1 indicates that tengine will certainly close the connection after a request.

Syntax: check_http_send http_packet
Default: "GET / HTTP/1.0\r\n\r\n"
Context: upstream

If the check type is http, the check function will send this http packet to the upstream server. Method "HEAD" is recommended for reducing traffic.

When persistant connection is used, a keep-alive request header should be added to the value of the directive, e.g. "HEAD / HTTP/1.1\r\nConnection: keep-alive\r\n\r\n".
In addition, in the case of "GET" method, size of the request uri should not be too large, make sure the transmission can be finished within an interval, otherwise the health check will deduce a conclusion that there is something wrong with the servers or the net.

Syntax: check_http_expect_alive [ http_2xx | http_3xx | http_4xx | http_5xx ]
Default: http_2xx | http_3xx
Context: upstream

These status codes indicate the upstream server's http response is OK and the check response is successful.

Syntax: check_shm_size size
Default: 1M
Context: http

Default size is one megabytes. If you want to check thousands of servers, the shared memory may be not enough, you can enlarge it with this directive.

Syntax: check_status [html|csv|json]
Default: check_status html
Context: location

Display the status of checking servers. This directive should be used in the http block.

You can specify the default display format after Tengine-1.4.0. The formats can be html, csv or json. The default type is html. It also supports to specify the format by the request argument. Suppose your check_status location is '/status', the argument of format can change the display page's format. You can do like this:


At present, you can fetch the list of servers with the same status by the argument of status. For example:


Below it's the sample html page:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN
<html xmlns="">
<title>Nginx http upstream check status</title>
<h1>Nginx http upstream check status</h1>
<h2>Check upstream server number: 1, generation: 3</h2>
<table style="background-color:white" cellspacing="0" cellpadding="3" border="1">
<tr bgcolor="#C0C0C0">
<th>Rise counts</th>
<th>Fall counts</th>
<th>Check type</th>
<th>Check port</th>

Below it's the sample of csv page:


Below it's the sample of json page:

{"servers": {
"total": 1,
"generation": 3,
"server": [
{"index": 0, "upstream": "backend", "name": "", "status": "up", "rise": 58, "fall": 0, "type": "http", "port": 80}