Prometheus Metrics in NodeJS

index.js

const metrics = require("./metrics");
...
server.pre(metrics.startMetrics(server));

metrics.js

const prom = require('prom-client');
const restify = require("restify");

const prom_metrics = {}

prom_metrics.status = new prom.Counter({
    name: 'status_codes',
    help: 'Path Status Code',
    labelNames: ['status_code']
});

prom_metrics.pathDuration = new prom.Histogram({
    name: 'path_duration',
    help: 'Duration for path',
    labelNames: ['path', 'status_code', 'method']
});

prom_metrics.pathCount = new prom.Counter({
    name: 'path_count',
    help: 'Number of paths',
    labelNames: ['path', 'status_code', 'method']
});

prom_metrics.pathDurationSummary = new prom.Summary({
    name: 'path_duration_summary',
    help: 'Summary of path durations',
    labelNames: ['path', 'status_code', 'method']
});

prom.collectDefaultMetrics();
prom.register.setDefaultLabels({ service: ''});

function create(){
    const server = restify.createServer({
        name: 'Metrics'
    });
    server.get("/prom/metrics",function(req, res, next){
        res.end(prom.register.metrics());
    })
    server.listen(8191, '0.0.0.0');
}
create();

function startMetrics(server){
    return function(req, res, next){
        server.on('after', restify.plugins.metrics({ server: server},
            function(err, metric, req, res, route){
                prom_metrics.pathDuration.observe({
                    path: metric.path,
                    status_code: metric.statusCode,
                    method: metric.method},metric.totalLatency);
                prom_metrics.pathDurationSummary.observe({
                    path: metric.path,
                    status_code: metric.statusCode,
                    method: metric.method
                }, metric.totalLatency);
                prom_metrics.status.inc({status_code: metric.statusCode});
                prom_metrics.pathCount.inc({
                    path: metric.path,
                    status_code: metric.statusCode,
                    method: metric.method
                });
            }));
        next();
    }
}
module.exports = exports = {
    startMetrics: startMetrics
}