Node - Redis Bandwidth Monitor

app.js

/*
npm install redis
*/
var http = require('http');
var fs = require('fs');
var redis = require("redis");
/* ------------------------------------------------------------------------------------------------ */
var server_id = 'source1';	// unique server id
var server_hostname = 'http://source1.domain.com';	// hostname
var server_network_interface = 'eth0';	// public network interface where nginx listens
var refresh_interval = 1000;	// bandwidth monitor refresh interval (ms)
var redis_host = '192.168.0.2';	// redis hostname or ip
var redis_port = 1234;	// redis port
var redis_password = 'SUPER_STRONG_PASSWORD_X80';	// redis password. Use strong password!
var redisHashKey = 'bandwidth:usage';	// redis key path (you don't need to change it)
/* ------------------------------------------------------------------------------------------------ */
var isFirst = true;
var previousValue = 0;
var currentValue = 0;
var usage = 0;
var redisDetails = {
    host: redis_host,
    port: redis_port,
    password: redis_password
};
var client = redis.createClient(redisDetails);

Array.prototype.getMin = function (attr) {
    return this.reduce(function (prev, curr) {
        return prev[attr] < curr[attr] ? prev : curr;
    });
}
setInterval(function () {
    getMetrics();
}, refresh_interval);
/**
 * Metrics
 */ 
 var getMetrics = function () {
    fs.readFile('/sys/class/net/' + server_network_interface + '/statistics/tx_bytes', function (err, buf) {
        currentValue = parseInt(buf.toString().replace(/\n/, ''));
        usage = currentValue - previousValue;
        if (!isFirst) {
            var bandwidthData = {'host': server_hostname, 'bandwidth': usage, 'last_update': new Date().getTime()};
            client.hset(redisHashKey, server_id, JSON.stringify(bandwidthData));
        } else {
            isFirst = false;
        }
        previousValue = currentValue;
    });
};
/**
 * Node Http Server
 */ 
 http.createServer(function (req, res) {
    client.hgetall(redisHashKey, function (error, object) {
        var container = [];
        for (var obj in object) {
            container.push(JSON.parse(object[obj]));
        }
        var result = container.getMin('bandwidth');
        res.writeHead(200, {"Content-Type": "application/json"});
        res.end(JSON.stringify(result));
    });
}).listen(3030, 'localhost');