Nodejs Event Driven Concurrency for Web Applications

Nodejs
Event-Driven concurrency for Web
Applications

Ganesh Iyer
@lastlegion
http://ganeshiyer.net

What is Node
Server-side JavaScript runtime


What is Node
Built on Google’s V8 Engine


What is Node

Why another server side technology?


What is Node

Uses an event-driven, non-blocking I/O model
for building scalable network applications


Concurrency in web
servers


Two main approaches

• Threads

• Events


Thread Based
• Creates a new thread( or process) for handling
a new connection.


Thread Based
a new connection.

Server Process

Thread Based
a new connection.

New
Connection

Server Process

Thread Based
a new connection.
Request
handler
Process
New
Connection

Server Process

Thread Based
a new connection.
Request
handler
Process

Server Process

Threads used in Apache(MPM)

Prefork


Threads used in Apache(MPM)

Worker

Scalability Issues

There is a maximum number of threads(T’) that a
system can support, beyond which the
throughput decreases.


Scalability Issues

Source: M. Welsh, S. D. Gribble, E. A. Brewer, and D. Culler. A design framework for highly con-current systems. Technical Report
UCB/CSD-00-1108, U.C. Berkeley Computer Science Division, April 2000.


Scalability Issues

Under heavy load a multi-threaded web
server consumers large amounts of memory


Scalability Issues

Single thread stack for each connection


Scalability Issues

Single thread stack for each connection

Overhead due to context-switching and
scheduling increases drastically with large
number of threads


Event Based


Event Based

States

Event Event Handler
Loop

Event Queue


Event Based
Event Emitters

States

Event Event Handler
Loop

Event Queue


Event Based
Use an event loop


Event Based
Use an event loop
Multiple connections are mapped to a single
thread.


Event Based
Use an event loop
Multiple connections are mapped to a single
thread.
This Thread handles all occurring events from
I/O operations of these connections and
requests.


Improved scalability

Source: M. Welsh, S. D. Gribble, E. A. Brewer, and D. Culler. A design framework for highly con-current systems. Technical Report
UCB/CSD-00-1108, U.C. Berkeley Computer Science Division, April 2000.


Improved scalability
The event loop has a queue of event handlers
that it executes in order.

The overhead when switching from one event
handler to the next time is much lower.


Nodejs


Why Server-side JavaScript?
Unified language for both front end an backend


Increased programmer productivity


Code reuse


Code reuse
exchange of data using JSON


Code reuse
Speed!


Code reuse
Speed! Contrary to popular belief, Javascript
with the V8 engine performs is faster than
PHP, Ruby and Python


Nodejs Architecture


Architecture

JavaScript

C++


Architecture

JavaScript

C++

JavaScript Engine

Architecture

JavaScript

C++

Event-based fully
asynchronous I/O library.


Architecture

JavaScript

C++

The event loop


Architecture

JavaScript

C++

Exposes OS features like
file handling, sockets
etc. Functionality for
HTTP, DNS etc http://ganeshiyer.net

The EventDriven model


Nodejs: Hello World


Nodejs: Hello World

Output
$ Hello World


Hello World revisited

VS

Synchronous Asynchronous



VS

Output
$ hello



VS

Output
$ hello 2 seconds later



VS

Output
$ hello 2 seconds later
$ world



VS

Output New request to
Node

$ hello During those two seconds



VS

Output New requests
to Node

$ hello During those two seconds



VS

Since it is non-blocking
Output
$ hello 2 seconds later $ hello 2 seconds later $ hello 2 seconds later
$ world $ world $ world

Response Response Response


Creating an HTTP server


Require http
module


Callback executed on
each request


Static file serving web server


Static file serving web server

Parsing
the url for
pathname


Node provides low-level functionality
For buliding web-applications we require higher
functionality
Node has a lot of packages that help!


Node Ecosystem


Package management with npm
Predominant package manager for node

To install ‘express’ package


Connect.js : Middleware for nodejs
Essential middleware required for developing
web applications

Implements logging, caching, cookies, sessions
etc.


Essential middleware required for developing web applications

• logger request logger with custom format support
• csrf Cross-site request forgery protection
• basicAuth basic http authentication
• bodyParser extensible request body parser
• json application/json parser
• urlencoded application/x-www-form-urlencoded parser
• cookieParser cookie parser
• session session management support with bundled MemoryStore
• cookieSession cookie-based session support
• staticCache memory cache layer for the static() middleware


Express.js : A MVC framework for web
Applications


Applications
Model View Controller


Applications

Performs RESTful routing


Applications

Performs RESTful routing
Uses Templating for rendering html


Scalability across multiple
cores/servers


cores/servers
Node is single threaded!


cores/servers
Node is single threaded!
How is going to scale on my multi-core server!?


cores/servers
Start child processes on multiple
cores/servers.

One process manages flow of events and
other cores for doing computation.


cores/servers

Cluster is an extensible multi-core server
manager for node.js.


Questions?


Thank You


Nodejs Event Driven Concurrency for Web Applications

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