Prometheus metrics for NGINX OSS using stub_status and js_body_filter

README.md

Prometheus metrics for NGINX open source

Converts the output of the NGINX stub_status module to Prometheus format so that basic metrics can be scraped from a /metrics endpoint.

The NGINX JavaScript module is used to filter the stub_status response.

$ curl -i http://localhost:8080/metrics
HTTP/1.1 200 OK
Server: nginx/1.21.3
Date: Thu, 21 Oct 2021 10:41:50 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive

connections{active} 1
connections{reading} 0
connections{writing} 1
connections{waiting} 0
server{accepts} 29
server{handled} 29
server{requests} 29

prometheus.js

var connection_vars = ['active', 'reading', 'writing', 'waiting'];
var server_vars =     ['accepts', 'handled', 'requests'];
var res = '';

function metrics(r, data, flags) {
    res += data;      // Collect the entire response,
    if (flags.last) { //  until we get the last byte.
        var metrics  = [];
        connection_vars.forEach(m => metrics.push(`connections{${m}} ${r.variables['connections_' + m]}`));
        var server_vals = res.split('\n')[2].trim().split(' ');
        for (var i = 0; i < server_vars.length; i++) {
            metrics.push(`server{${server_vars[i]}} ${server_vals[i]}`);
        }
        r.sendBuffer(metrics.join('\n') + '\n', flags);
    }
}

function nolength(r) {
    delete r.headersOut['Content-Length'];
}

export default { metrics, nolength }

stub_metrics.conf

js_import conf.d/prometheus.js;

server {
    listen 8080;

    location = /metrics {
        stub_status;
        js_header_filter prometheus.nolength;
        js_body_filter   prometheus.metrics;
    }

    location = /status {
        stub_status;
    }

    location / {
        default_type application/json;
        return 200 '["/metrics", "/status"]\n';
    }
}

# vim: syntax=nginx