Monitoring App

I recently started trying to create a setup that can monitor CPU and RAM usage on a remote server. After quite a bit of thinking I created a SQL database and shell script that saved outputted data into the DB. This wasn’t ideal for remote servers so I created a poor man’s API with Node & Express. It takes a web call from remote systems running a shell script on a schedule. It then saves it to a table and I’m using grafana to visualize the data. Its in a super early state now with no validation but it is functional. Here’s my code for Node:

 

var express = require('express');

var router = express.Router();

var bodyParser = require('body-parser');

var mysql = require('mysql');

var con = mysql.createConnection({

host:"localhost",

user:"perfmon",

password:"passwordhere",

database:"perfmon"

});

con.connect(function (err) {

if (err) throwerr;

console.log("Connected to SQL database");

});

/* GET home page. */

router.get('/', function (req, res, next) {

varserverName=req.query.serverName;

varCPU=req.query.CPU;

varRAM=req.query.RAM;

//sqlInsertPerfmon = "INSERT INTO serverbuilddata (ServerName, CPUCount, RAMCount) VALUES ('" + serverName + "'," + CPUCount + "," + serverMemory + ');'

sqlInsertPerfmon="INSERT INTO perfdata (serverName, CPU, RAM) VALUES ('"+serverName+"',"+CPU+","+RAM+");"

console.log('SQL Statement: '+sqlInsertPerfmon);

con.query(sqlInsertPerfmon, function (err, result) {

if (err) throw(err);

console.log("Performance Data Logged");

res.render('perfmon', { title:'Perfmon', serverName:serverName, CPU:CPU, RAM:RAM });

});




});

module.exports = router;

Learning about NodeJS, ExpressJS, and other components of server side javascript

Recently I’ve been learning about NodeJS and how to write server side JavaScript. This week I was creating a route that pulled variables from¬† POST, inserted them into a SQL database, and then retrieved the ID of the inserted record. Later on I wanted to take that ID and retrieve the record submitted. When the code ran I didn’t have errors but I had symptoms that didn’t make sense. As my debugging strategy I started logging variables to make sure they had values that I expected.

sqlInsertServer = "INSERT INTO serverbuilddata (ServerName, CPUCount, RAMCount) VALUES ('" + serverName + "'," + CPUCount + "," + serverMemory + ');'
console.log('SQL Statement: ' + sqlInsertServer);
var buildID;
con.query(sqlInsertServer, function (err, result) {
if (err) throw(err, null);
buildID = result.insertId;
console.log("Inside function. Server record inserted. Build ID: " + buildID);
);
console.log(buildID);

The first instance of build ID I logged inside the function returned the correct result, but the one outside of the function was undefined. I thought it was a scoping problem at first and tried to make sure the variable was declared globally. Then I noticed that the undefined variable outside the function was being logged before the one in the function. Then it kind of clicked about how Node is asynchronous. It doesn’t wait for other functions to run before the code gets executed even if they are in the correct order. After some research about my options I decided to go with call backs since they seemed to be the most recommended and best way.

sqlInsertServer = "INSERT INTO serverbuilddata (ServerName, CPUCount, RAMCount) VALUES ('" + serverName + "'," + CPUCount + "," + serverMemory + ');'
console.log('SQL Statement: ' + sqlInsertServer);

function serverInsert(callback) {
var buildID;
con.query(sqlInsertServer, function (err, result) {
if (err) callback(err, null);
buildID = result.insertId;
callback(null, buildID);
console.log("Inside function. Server record inserted. Build ID: " + buildID);
});
}

serverInsert(function (err, buildID) {
if (err) {
// error handling code goes here
console.log("ERROR : " + err);
} else {
// code to execute on data retrieval
console.log("result from callback is : " + buildID);
})

Callbacks wait for the function to provide it with a value. The problem is that value still can’t be used outside the function. And if that value in the callback needs to be used in another SQL function you need to nest another callback in the callback. Before you know it you have a mess. It does work but I’m still looking for better ways to do it. I’ve read about promises but I’m not ready for that yet.