Module ngx_http_upstream_hc_module

Example Configuration
Directives
     health_check
     match

The ngx_http_upstream_hc_module module allows enabling periodic health checks of the servers in a group referenced in the surrounding location. The server group must reside in the shared memory.

If a health check fails, the server will be considered unhealthy. If several health checks are defined for the same group of servers, a single failure of any check will make the corresponding server be considered unhealthy. Client requests are not passed to unhealthy servers and servers in the “checking” state.

Please note that most of the variables will have empty values when used with health checks.

This module is available as part of our commercial subscription.

Example Configuration

upstream dynamic {
    zone upstream_dynamic 64k;

    server backend1.example.com      weight=5;
    server backend2.example.com:8080 fail_timeout=5s slow_start=30s;
    server 192.0.2.1                 max_fails=3;

    server backup1.example.com:8080  backup;
    server backup2.example.com:8080  backup;
}

server {
    location / {
        proxy_pass http://dynamic;
        health_check;
    }
}

With this configuration, nginx will send “/” requests to each server in the backend group every five seconds. If any communication error or timeout occurs, or a proxied server responds with the status code other than 2xx or 3xx, the health check will fail, and the server will be considered unhealthy.

Health checks can be configured to test the status code of a response, presence of certain header fields and their values, and the body contents. Tests are configured separately using the match directive and referenced in the match parameter of the health_check directive:

http {
    server {
    ...
        location / {
            proxy_pass http://backend;
            health_check match=welcome;
        }
    }

    match welcome {
        status 200;
        header Content-Type = text/html;
        body ~ "Welcome to nginx!";
    }
}

This configuration shows that in order for a health check to pass, the response to a health check request should succeed, have status 200, and contain “Welcome to nginx!” in the body.

Directives

Syntax: health_check [parameters];
Default:
Context: location

Enables periodic health checks of the servers in a group referenced in the surrounding location.

The following optional parameters are supported:

interval=time
sets the interval between two consecutive health checks, by default, 5 seconds.
jitter=time
sets the time within which each health check will be randomly delayed, by default, there is no delay.
fails=number
sets the number of consecutive failed health checks of a particular server after which this server will be considered unhealthy, by default, 1.
passes=number
sets the number of consecutive passed health checks of a particular server after which the server will be considered healthy, by default, 1.
uri=uri
defines the URI used in health check requests, by default, “/”.
mandatory
sets the initial “checking” state for a server until the first health check is completed (1.11.7). Client requests are not passed to servers in the “checking” state. If the parameter is not specified, the server will be initially considered healthy.
match=name
specifies the match block configuring the tests that a response should pass in order for a health check to pass. By default, the response should have status code 2xx or 3xx.
port=number
defines the port used when connecting to a server to perform a health check (1.9.7). By default, equals the server port.

Syntax: match name { ... }
Default:
Context: http

Defines the named test set used to verify responses to health check requests.

The following items can be tested in a response:

status 200;
status is 200
status ! 500;
status is not 500
status 200 204;
status is 200 or 204
status ! 301 302;
status is neither 301 nor 302
status 200-399;
status is in the range from 200 to 399
status ! 400-599;
status is not in the range from 400 to 599
status 301-303 307;
status is either 301, 302, 303, or 307

header Content-Type = text/html;
header contains “Content-Type” with value text/html
header Content-Type != text/html;
header contains “Content-Type” with value other than text/html
header Connection ~ close;
header contains “Connection” with value matching regular expression close
header Connection !~ close;
header contains “Connection” with value not matching regular expression close
header Host;
header contains “Host”
header ! X-Accel-Redirect;
header lacks “X-Accel-Redirect”

body ~ "Welcome to nginx!";
body matches regular expression “Welcome to nginx!
body !~ "Welcome to nginx!";
body does not match regular expression “Welcome to nginx!

require $variable ...;
all specified variables are not empty and not equal to “0” (1.15.9).

If several tests are specified, the response matches only if it matches all tests.

Only the first 256k of the response body are examined.

Examples:

# status is 200, content type is "text/html",
# and body contains "Welcome to nginx!"
match welcome {
    status 200;
    header Content-Type = text/html;
    body ~ "Welcome to nginx!";
}

# status is not one of 301, 302, 303, or 307, and header does not have "Refresh:"
match not_redirect {
    status ! 301-303 307;
    header ! Refresh;
}

# status ok and not in maintenance mode
match server_ok {
    status 200-399;
    body !~ "maintenance mode";
}

# status is 200 or 204
map $upstream_status $good_status {
    200 1;
    204 1;
}

match server_ok {
    require $good_status;
}