Learn here how to use the foglet-core library to build fog computing applications.
foglet-core allows to build fog computing applications, i.e., applications that runs in a fiog of browsers.
Such application is called a Foglet.
A Foglet connect browsers through a Random Peer Sampling (RPS) overlay network [1]. Such a network approximates a random graph where each data consumer is connected to a fixed number of neighbors. It is resilient to churn, to failures and communication with neighbors is a zero-hop.
In the context of browsers, basic communications rely on WebRTC to establish a data-channel between browsers and SPRAY [2] to enable RPS on WebRTC. Each browser maintains a set of neighbors K called a view that is a random subset of the whole network. To keep its view random, a data consumer renews it periodically by shuffling its view with the view of a random neighbor.
As a Foglet rely on WebRTC for communication, it requires a signaling server to disocver new peers and ICE servers to connect browsers, throught NAT for example. These points will be discussed in details later.
To demonbstrate all key concepts of a Foglet, let's build a Hello world aplication. it will be a simple Foglet that broadcast the message hello world! to all connected browsers.
All code written during this tutorial can be found on this repository.
First, setup a new npm project
mkdir foglet-hello-world
cd foglet-hello-world
npm init
Next, install the core library and the development tools for foglet apps
npm install --save foglet-core
npm install --save-dev foglet-scripts
Edit your package.json file to add the following fields:
"scripts: {
"start": "foglet-scripts start"
}Now, create the following files
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Foglet Hello world</title>
</head>
<body>
<button id="send-message">Hello World!</button>
<!-- foglet-core bundle -->
<script src="node_modules/foglet-core/dist/foglet.bundle.js"></script>
<script src="app.js"></script>
</body>
</html>app.js
'use strict'
console.log('hello world')To test your installation, open index.html in a browser, you should see hello world! in the console.
Now that's your project is ready, let's create our Hello World Foglet. Here is the complete code to put in index.js.
NB: Notice that we use a require style syntax here to import dependencies, as foglet-core bundle is built using Browserify
'use strict'
const Foglet = require('foglet').Foglet
const app = new Foglet({
verbose: true, // activate logs. Put false to disable them in production!
rps: {
type: 'spray-wrtc',
options: {
protocol: 'foglet-hello-world', // name of the protocol run by your app
webrtc: { // WebRTC options
trickle: true, // enable trickle (divide offers in multiple small offers sent by pieces)
iceServers : [] // iceServers, we lkeave it empty for now
},
timeout: 2 * 60 * 1000, // WebRTC connections timeout
delta: 10 * 1000, // spray-wrtc shuffle interval
signaling: { //
address: 'http://localhost:3000/',
room: 'foglet-hello-world-room' // room to join
}
}
}
})
// connect to the signaling server
app.share()
// connect our app to the fog
app.connection()
.then(() => {
console.log('application connected!')
// listen for incoming broadcast
app.onBroadcast((id, msg) => {
console.log('I have received a message from peer', id, ':', msg)
})
// send our message each time we hit the button
const btn = document.getElementById("send-message")
btn.addEventListener("click", () => {
app.sendBroadcast('hello World!')
}, false)
})
.catch(console.error) // catch connection errorsNow, run npm start to start the signaling server, and then open index.html in two tabs, to create two distinct peers.
Open the console, wait for connections to be done, and then click those damn buttons! You should see messages popping in each tab!
A signaling server acts as a forwarding server in order to connect all new peers on the specified room. You can access an implenmentation at https://github.com/RAN3D/foglet-signaling-server
However, if you juste need a signaling server out of the box, the foglet build tools contains one that can
be run with foglet-scripts start.
Work in prgress
A complete and usefull documentation is available here
In short: when your are in a local network, you don't need to use ICE. But if you want to contact a peer on the other side of the world, you may have to pass through firewalls and all sort of things. ICE servers are here to resolve this.