Proper way to monitor/control a server remotely over http in realtime

Question

On my client (a phone with a browser) I want to see the stats of the server CPU,RAM & HDD and gather info from various logs.

I'm using ajax polling.

On the client every 5 sec (setInterval) I call a PHP file:

1. scan a folder containing N logs

2. read the last line of each log

3. convert that to JSON

Problems:

1. Open new connection every 5 sec.
2. Multiple AJAX calls.
3. Request headers (they are also data and so consume bandwidth)
4. Response headers (^)
5. Use PHP to read files every 5 sec. even if nothing changed.

The final JSON data is less than 5 KB, but I send it every 5 sec, and there are the headers and new connection every time, so basically every 5 sec., I have to send 5-10 KB to get 5 KB which are 10-20 KB.

Those are 60 sec / 5 sec = 12 new connections per minute and about 15 MB per hour of traffic if I leave the app open.

Lets say I have 100 users that I let monitor / control my server that would be around 1.5 GB outgoing traffic in one hour.

Not to mention that the PHP server is reading multiple files 100 times every 5 sec.

I need something that on the server reads the last lines of those logs every 5 sec and maybe writes them to a file, then I want to push this data to the client only if it's changed.

---

SSE (server sent events) with PHP

header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');
while(true){
 echo "id: ".time()."\ndata: ".ReadTheLogs()."\n\n";
 ob_flush();
 flush();
 sleep(1);
}

In this case after the connection is established with the first user the connection keeps open (PHP is not made for that) and so I save some space (request headers,response headers). This work on my server bu most server don't allow to keep the connection open for long time.

Also with multiple users I read the log multiple times.(slowing down my old server) And I can't control the server ... I would need to use ajax to send a command...

I need WebSockets!!!

---

node.js and websockets

using node.js, from what i understand, i can do all this without consuming alot of resources and bandwich. The connection keeps open so no unnecessary headers, i can recieve and send data.it handles multiple users very well.

And this is where i need your help.

1. the node.js server should in background update, and store the logs data every 5 sec if the files are modified.OR should that do the operating system with (iwatch,dnotify...)

2. the data should be pushed only if changed.

3. the reading of the logs should be happen only one time after 5 sec ... so not triggered by each user.

---

this is the first example i have found.....and modified..

var ws=require("nodejs-websocket");
var server=ws.createServer(function(conn){

    var data=read(whereToStoreTheLogs);
    conn.sendText(data)// send the logs data to the user 
    //on first connection.

    setTimeout(checkLogs,5000);
    /*
     here i need to continuosly check if the logs are changed.
     but if i use setInterval(checkLogs,5000) or setTimeout
     every user invokes a new timer and so having lots of timers on the server
     can i do that in background?         
    */
    conn.on("text",function(str){
     doStuff(str); // various commands to control the server.
    })
    conn.on("close",function(code,reason){
     console.log("Connection closed")
    })
}).listen(8001);

var checkLogs=function(){
 var data=read(whereToStoreTheLogs);
 if(data!=oldData){
  conn.sendText(data)
 }
 setTimeout(checkLogs,5000);
}

the above script would be the notification server, but i also need to find a solution to store somwhere the info of those multiple logs and do that everytime something is changed, in the background.

How would you do to keep the bandwich low but also the server resources.

How would you do?

EDIT Btw. is there a way to stream this data simultaneosly to all the clinets?

EDIT

About the logs: i also want to be able to scale the time dilatation between updates... i mean if i read the logs of ffmpeg i ned the update every sec if possible... but when no conversion is active.. i need to get the basic machine info every 5min maybe ... and so on...

GOALS: 1. performant way to read & store somewhere the logs data (only if clinets connected...[mysql,file, it's possible to store this info inside the ram(with node.js??)]). 2. performant way to stream the data to the various clients (simultanously). 3. be able to send commands to the server.. (bidirectional) 4. using web languages (js,php...), lunix commands( something that is easy to implement on multiple machines).. free software if needed.

best approach would be:

read the logs, based on current activity, to the system memory and stream simultaneously and continuosly, with an already open connection, to the various clients with webSockets.

i'don't know anything that could be faster.

UPDATE

The node.js server is up and running, using the http://einaros.github.io/ws/ webSocketServer implementation, as it appears to be the fastest one. I wrote with the help of @HeadCode the following code to handle properly the client situation & to keep the process as low as possible. checking various things inside the broadcast loop. Now the pushing & the client handling is at a good point.

var 
wss=new (require('ws').Server)({port:8080}),
isBusy,
logs,
clients,
i,
checkLogs=function(){
 if(wss.clients&&(clients=wss.clients.length)){
  isBusy||(logs=readLogs()/*,isBusy=true*/);
  if(logs){
   i=0;
   while(i<clients){
    wss.clients[i++].send(logs)
   }
  }
 } 
};
setInterval(checkLogs,2000);

But atm i'm using a really bad way to parse the logs.. (nodejs->httpRequest->php).. lol. After some googling i found out that i totally could stream the output of linux software directly to the nodejs app ... i didn't checked... but maybe that would be the best way to do it. node.js also has a filesystem api where icould read the logs. linux has it's own filesystem api.

the readLogs()(can be async) function is still something i'm not happy with.

1. nodejs filesystem?
2. linuxSoftware->nodejs output implementation
3. linux filesystem api.

keep in mind that i need to scan various folders for logs and then parse somehow the outputted data, and this every 2 seconds.

ps.: i adde isBusy to the server variables in case the logReading sytem is async.

EDIT

Answer is not complete.

Missing:

1. A performant way to read,parse and store the logs somewhere (linux filesystem api, or nodejs api, so the i store directly into system memory)
2. An explaination if it's possible to stream data directly to multiple users . apparently nodejs loops trough the clients and so (i think) sending multiple times the data.

btw is it possible/worth to close the node server if there are no clients and restart on new connections on the apache side. (ex: if i connect to the apache hosted html file a script launches the nodejs server again). doing so would further reduce the memory leaking???right?

EDIT

After some experimenting with websockets (some videos are in the comments) i learned some new stuff. Raspberry PI has the possibility to use some CPU DMA channels to to high frequency stuff like PWM... i need to somehow understand how that works.

When using sensors and stuff like that i should store everything inside the RAM, nodejs already does that?? (in a variable inside the script)

websocket remains the best choice as it's basically easely accessible from any device now, simply using a browser.

Answer 1

I haven't used nodejs-websocket, but it looks like it will accept an http connection and do the upgrade as well as creating the server. If all you care about receiving is text/json then I suppose that would be fine, but it seems to me you might want to serve a web page along with it.

Here is a way to use express and socket.io to achieve what you're asking about:

var express = require('express');
var app = express();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.use(express.static(__dirname + '/'));
app.get('/', function(req, res){
    res.sendfile('index.html');
});

io.on('connection', function(socket){

    // This is where we should emit the cached values of everything
    // that has been collected so far so this user doesn't have to
    // wait for a changed value on the monitored host to see
    // what is going on.
    // This code is based on something I wrote for myself so it's not
    // going to do anything for you as is.  You'll have to implement
    // your own caching mechanism.
    for (var stat in cache) {
        if (cache.hasOwnProperty(stat)) {
            socket.emit('data', JSON.stringify(cache[stat]));
        }
    }
});

http.listen(3000, function(){
    console.log('listening on *:3000');
});

(function checkLogs(){
    var data=read(whereToStoreTheLogs);
    if(data!=oldData){
        io.emit(data)
    }
    setTimeout(checkLogs,5000);
})();

Of course, the checkLogs function has to be fleshed out by you. I have only cut and pasted it in here for context. The call to the emit function of the io object will send the message out to all connected users but the checkLogs function will only fire once (and then keep calling itself), not every time someone connects.

In your index.html page you can have something like this. It should be included in the html page at the bottom, just before the closing body tag.

<script src="/path/to/socket.io.js"></script>
<script>

    // Set up the websocket for receiving updates from the server
    var socket = io();

    socket.on('data', function(msg){
        // Do something with your message here, such as using javascript
        // to display it in an appropriate spot on the page.
        document.getElementById("content").innerHTML = msg;
    });

</script>

By the way, check out the Nodejs documentation for a variety of built-in methods for checking system resources (https://nodejs.org/api/os.html).

Here's also a solution more in keeping with what it appears you want. Use this for your html page:

<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>WS example</title>
</head>
<body>
<script>
var connection;
window.addEventListener("load", function () {
    connection = new WebSocket("ws://"+window.location.hostname+":8001")
    connection.onopen = function () {
        console.log("Connection opened")
    }
    connection.onclose = function () {
        console.log("Connection closed")
    }
    connection.onerror = function () {
        console.error("Connection error")
    }
    connection.onmessage = function (event) {
        var div = document.createElement("div")
        div.textContent = event.data
        document.body.appendChild(div)
    }
});
</script>
</body>
</html>

And use this as your web socket server code, recently tweaked to use the 'tail' module (as found in this post: How to do `tail -f logfile.txt`-like processing in node.js?), which you will have to install using npm (Note: tail makes use of fs.watch, which is not guaranteed to work the same everywhere):

var ws = require("nodejs-websocket")
var os = require('os');
Tail = require('tail').Tail;
tail = new Tail('./testlog.txt');

var server = ws.createServer(function (conn) {
    conn.on("text", function (str) {
        console.log("Received " + str);
    });
    conn.on("close", function (code, reason) {
        console.log("Connection closed");
    });
}).listen(8001);


setInterval(function(){ checkLoad(); }, 5000);


function broadcast(mesg) {
    server.connections.forEach(function (conn) {
        conn.sendText(mesg)
    })
}

var load = '';
function checkLoad(){
    var new_load = os.loadavg().toString();
    if (new_load === 'load'){
        return;
    }
    load = new_load;
    broadcast(load);
}

tail.on("line", function(data) {
    broadcast(data);
});

Obviously this is very basic and you will have to change it for your needs.