Technology Stack

AngularJS

• Front-End Framework
• Backed by Google
• Easy to learn

NodeJS

• Javascript Runtime Engine
• To build server and networking apps
• Very very very fast even on high-loads
• V8 by Google

Short Polling

Poor-mans' Realtime Engine

How Short-polling Works

Short-polling Example

> node ex1.js 

Pros

• Simplest implementation
• Requests are short-lived
• HTTP - Will probably work no matter what
• Supported on all clients
• Supported on all servers

Cons

• Requests are short-lived - HTTP is expensive
• Lag not the best user experience
• Most requests return empty result
• Cookies are sent together

To Use

• You like request - response pattern
• You want something that "Just Works"
• You are afraid of long-running processes and memory leaks

Don't Use

• Latency sensitive (Gaming)

Long Polling

Getting rid of excess fat

How Long Polling Works

Long-polling Example

> node ex2.js 

Pros

• HTTP connection always on, less overhead
• Almost no-lag
• HTTP - Will probably work no matter what
• Supported on all clients
• Supported on all servers with modification

Cons

• Requests are long-lived - check for memory leaks
• Have to implement some sort of realtime DB or caching
• Server has to be configured to handle these types of request
• Uses up your AJAX quota

To Use

• You want a responsive backend
• You already have short-polling and need to scale fast and without infra change

Don't Use

• You do a lot of AJAX
• Your server has hard limits for max open connections
• You are not comfortable with long-running process

Server Sent Events

Leaner than lean

How SSE Works

SSE Example

> node ex3.js 

Pros

• Stateless HTTP connection always on, no HTTP overhead
• HTTP - Will probably work no matter what
• Auto negotiation and reconnection
• Built-in queueing
• Doesn't use up your AJAX quota
• Supported on most clients
• Supported on all servers with modification

Cons

• Requests are long-lived - check for memory leaks
• Have to implement some sort of realtime DB or caching
• Server has to be configured to handle these types of request
• Relatively newer than AJAX
• Not supported on IE
• Stateless

To Use

• You want a responsive backend
• Data is broadcast one to many
• Bandwidth and server resources conscious

Don't Use

• Your server has hard limits for max open connections
• Data broadcasted is unique to each user
• You are not comfortable with long-running process
• Your end users are mainly running IE

Websockets

Latest & Greatest

How Websockets Works

Websocket Example

> node ex4.js 

Pros

• Stateless connection always on, no HTTP overhead
• Two-way realtime non-blocking socket
• Supported on most clients

Cons

• Requests are long-lived - check for memory leaks
• Have to implement some sort of realtime DB or caching
• Not all servers has implementation for WS
• Newest technology to communicate realtime 
• Some network devices does not WS passthru support (proxy, firewalls)

To Use

• You want a responsive backend
• Data goes both ways
• Best usecase: MMORPG
• Future applications

Don't Use

• You are not comfortable with long-running process
• You are not looking into revamping your whole system
• Your network does not support it