Upstream Probe

The module implements active health probes for stream_upstream.

Configuration Example

server {
    listen ...;

    # ...
    proxy_pass backend;
    upstream_probe_timeout 1s;

    upstream_probe backend_probe
        port=12345
        interval=5s
        test=$good
        essential
        fails=3
        passes=3
        max_response=512k
        mode=onfail
        "send=data:GET / HTTP/1.0\n\n";
}

Directives

upstream_probe (PRO)

Added in version 1.4.0: PRO

Syntax	upstream_probe name [port=number] [interval=time] [test=condition] [essential [persistent]] [fails=number] [passes=number] [max_response=size] [mode=always | idle | onfail] [udp] [send=string];
Default	—
Context	server

Defines an active health probe for peers within the upstream groups that are specified for proxy_pass in the same location context with the upstream_probe directive. Subsequently, Angie regularly probes each peer of the upstream group according to the parameters configured here.

A peer's probe is passed if the request to the peer succeeds, considering all parameter settings of the upstream_probe directive and the settings that control how upstreams are used by the directive's location context, including the proxy_next_upstream directive.

To make use of the probes, the upstream must have a shared memory zone (zone). One upstream may be configured with several probes.

The following parameters are accepted:

name	Mandatory name of the probe.
port	Alternative port number for the probe request.
interval	Interval between probes. By default — 5s.
test	The condition for the probe, defined as a string of variables. If the variables' substitution yields "" or "0", the probe is not passed.
essential	If set, the initial state of the peer is being checked, so the peer doesn't receive client requests until the probe is passed.
persistent	Setting this parameter requires enabling essential first; persistent peers that were deemed healthy prior to a configuration reload start receiving requests without being required to pass this probe first.
fails	Number of subsequent failed probes that renders the peer unhealthy. By default — 1.
passes	Number of subsequent passed probes that renders the peer unhealthy. By default — 1.
max_response	Maximum memory size for the response. If a zero value is specified, response waiting is disabled. By default — 256k.
mode	Probe mode, depending on the peers' health: always — peers are probed regardless of their state; idle — probes affect unhealthy peers and peers where interval has elapsed since the last client request. onfail — only unhealthy peers are probed. By default — always.
udp	If specified, the UDP protocol is used for probing. By default, TCP is used for probing.
send	Data sent for the check; this can be a string with the prefix data: or a file name with data (specified absolutely or relative to the /usr/local/angie/ directory).

Example:

upstream backend {
    zone backend 1m;

    server a.example.com;
    server b.example.com;
}

map $upstream_probe_response $good {
    ~200    "1";
    default  "";
}

server {
    listen ...;

    # ...
    proxy_pass backend;
    upstream_probe_timeout 1s;

    upstream_probe backend_probe
        port=12345
        interval=5s
        test=$good
        essential
        persistent
        fails=3
        passes=3
        max_response=512k
        mode=onfail
        "send=data:GET / HTTP/1.0\n\n";
}

Details of probe operation:

• Initially, the peer won't receive client requests until it passes all essential probes configured for it, skipping persistent ones if the configuration was reloaded and the peer was deemed healthy prior to that. If there are no such probes, the peer is considered healthy.

• The peer is considered unhealthy and won't receive client requests, if any of the probes configured for it hits fails or the peer reaches max_fails.

• For an unhealthy peer to be considered healthy again, all probes configured for it must reach their respective passes; after that, max_fails is also considered.

Built-in Variables

The stream_upstream module supports the following built-in variables:

$upstream_probe (PRO)

Name of the currently active upstream_probe.

$upstream_probe_response (PRO)

Contents of the response received during an active probe configured by upstream_probe.