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In Real Time - The Beginning
Kristian Ačkar

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A little about me...
Kristian Ačkar - employed in Core Incubator
● “System Analysis & Traffic. With a sparkle in his eye and
passion for football”
“Core Incubator is an angel investor, providing pre-seed
and seed investment of a small scale. We are also a
startup hub offering coworking space and mentorship,
for startups eager to grow and develop.” - www.coreincubator.com
Contact me:
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3.
What to expect ahead...
● Introduction
● What can you do with Node.js
● When to use Node.js and when not
● Scalability
● Node.js ecosystem
● Socket.io
● Who uses Node.js
● Zdravko Mamić
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4.
Background
● Node.js is an open-source cross-platform JavaScript runtime built on
Chrome’s V8 JavaScript engine
● Originally written in 2009 by Ryan Dahl
● Latest stable release v5.5.0
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Introduction: Basic
● Node.js is “server side JavaScript”
● High-performance network applications framework
● Optimized for high concurrent environments
● ~40% written in JavaScript and ~60% in C++
“As an asynchronous event driven framework, Node.js is designed to build
scalable network applications” - from nodejs.org
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Introduction: Advanced
● Node.js uses an event-driven, non-blocking I/O model
● It makes use of event-loops via JavaScript’s callback functionality to
implement the non-blocking I/O
● Most of familiar JavaScript from browser is ported to Node.js, except the
DOM/BOM implementation
var x = document.getElementsByTagName(“p”)
var y = window.innerWidth
● Everything inside Node.js runs in a single-thread
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Introduction: Some (confusing) theory (1)
Event-loops
● Core of event-driven programming (almost all the UI programs use event-
loops to track the user event)
● A major usage of JavaScript is to interact with the DOM (browser) - use of
event-based API was natural
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File System
Database
Network
...
INTENSIVE
OPERATION
EVENT
QUEUE
Register Callback
Operation Complete
Trigger Callback
EVENT LOOP
(single thread)

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Introduction: Some (confusing) theory (2)
Non-blocking I/O
fs.unlinkSync(“/tmp/hello”);
console.log(“I was blocked”); // execution is blocked
fs.unlink(“/tmp/hello”, (err) => {
if (err) throw err;
console.log(“/tmp/hello deleted”);
});
console.log(“I wasn’t blocked”); // execution is not blocked
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9.
What can you do with Node.js
● All kind of servers
○ HTTP server
○ TCP server Example: TCP client - server
○ DNS server
○ Static file server
● Real-time applications
○ Chat
○ Online games
○ Collaboration tools Example: Drawing collaborating tool
○ Anything which sends updates to the user in real-time
● Desktop GUI applications
● Any kind of applications
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10.
When to use Node.js and when not
Use Node.js
● For applications where you’d like to maintain persistent connection from the
browser back to the server (“long-polling”)
● When you can reuse a lot of code across the client/server gap (Meteor.js)
● For applications that have a lot of concurrent connections and each request
only needs very few CPU cycles (because the event loop is blocked during
execution of a function)
Don’t use Node.js
● When server request is dependant on heavy CPU consuming algorithm/job
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Scalability
● Horizontal scalability is problem
● Adding more CPU cores won’t increase performance
● SOLUTION
○ Utilize multi-core CPUs e.g. by setting up cluster (nodejs.org/api/cluster.html)
○ Setup a load balancer and spin up more servers
Example: Node.js clustering
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Scalability: clusters increase performance
● Apache Benchmark
● 8 core CPU
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Concurrent Connections 1 2 4 8 16
Single Process 654 711 783 776 754
8 Workers 594 1198 2110 3010 3024

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Node.js ecosystem (1)
● Node.js framework is structured in modules
○ Core modules (fs, cluster, http, net, dgram, crypto, ...)
○ Custom modules
const PI = Math.PI;
exports.area = function(r) {
return PI * r * r;
}
exports.circumference = function(r) {
return 2 * r * PI;
}
const circle = require(“./circle.js”);
console.log(“The area of a circle of radius 10 is ${circle.area(10)}”);
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circle.js
demo.js

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Node.js ecosystem (2)
Node Package Manager - NPM (www.npmjs.com)
● Node.js packages repository
● Package is custom made module published in the repository (available to community)
● Real power of Node.js (238 635 packages in repository)
○ Production development heavily depends on Node.js packages
● Countless number of downloads
○ 147 308 788 in the last day
○ 816 096 961 in the last week
○ 3 447 929 034 in the last month
● Install local or global
○ npm install -g sails@0.12.0 vs npm install sails@0.12.0
● Node.js project can define list of dependencies in a package.json file (example)
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Socket.io
● Node.js (JavaScript) is event driven system
○ Usually we handle events immediately - real-time
■ e.g. file watching example - isn’t that example of “real time“ app?
● Most of the time when we talk about “real-time” and Node.js we mean on one
of the most popular Node.js module - socket.io (http://socket.io)
○ Uses websocket protocol to communicate with a server
○ Simple and lightweight
○ Uses “heartbeats” to control connection health
○ Server can separate socket connections into “rooms”
■ Example apps: chat systems with rooms, brazuca
Example: Drawing collaborating tool
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16.
Who uses Node.js (in production)
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● Big shots
○ github.com/nodejs/node-v0.x-archive/wiki/Projects,-Applications,-and-Companies-Using-Node

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End of presentation…
...start of discussion 17