Web Application + Software Architecture

Question 1

What is Web Architecture?

Answer 1

Multiple components (DBs, message queue, cache, UI) all running in conjunction to form an online service

Question 2

What is Client-Server Architecture?

Answer 2

Fundamental Building Block of the Web
Request-Response model - Client sends request to server for info, server responds with it.

Question 3

What is a Thin Client?

Answer 3

Client that Just holds the UI of the app. No business logic. No business Logic.

For every action, client sends request to backend (just like 3-Tier App)

Question 4

What is a Thick/Fat Client?

Answer 4

Holds all or some part of the business logic + the UI

Question 5

When to use Thick Client?

Answer 5

When we need to minimize the network latency and reduce network calls to backend server. Keeps latency of the app low.

Need to reduce bandwidth consumption in the client server for a smoother user experience. Enhances user experience, reduces latency.

Question 6

What is a web server?

Answer 6

A component in web application infrastructure.

Receives requests from client and sends response AFTER executing business logic, based on parameters sent from the client.

Question 7

What is an application server?

Answer 7

A server running a web app.

Every service needs a server to run.

Question 8

List some types of web server based on their core task

Answer 8

Proxy Server
Mail Server
File Server
Virtual Server
Data Storage Server
Batch Job server

Question 9

What is a Request-Response Model?

Answer 9

Client and servers have a request-response model…no request, there is no response.

Question 10

What is the HTTP Protocol?

Answer 10

Protocol for data exchange over World Wide Web.

Stateless protocol. Every request independent, has no knowledge of previous

Question 11

What is a REST API?

Answer 11

Representational State Transfer - Architecture Style for building web services

Question 12

What requirements do APIs need to adhere to in order to be REST compliant?

Answer 12

API must act as an interface

API must provide communication between client/server over HTTP Protocol

Communication must be stateless - every new request is completely independent of the last/next

API must send Auth info with every request

Question 13

What is HTTP PULL data transfer between client and server?

Answer 13

Client sends request to server. Client pulls data from server whenever required. Done over and over to fetch latest data.

Question 14

What is HTTP PUSH data transfer between client and server?

Answer 14

Keeps the server from being brought down by excessive HTTP requests. Uses Callbacks to to allow server to keep sending updates to clients when they’re available

Question 15

What is a Callback for the HTTP Push Mechanism?

Answer 15

Mechanism for client to send request for certain info once. After the first request, server keeps pushing updates to client once they’re available.

Question 16

Benefit of HTTP PUSH?

Answer 16

Saves network bandwidth. Cuts down load on server

Question 17

Examples of HTTP PUSH Implementations?

Answer 17

AJAX Long Polling
Web Sockets
HTML5 Event Source
Streaming over HTTP
Message Queues

Question 18

When to use HTTP PUSH?

Answer 18

Real-time applications like online multiplayer games, a LIVE sports app, etc

When we need to reduce the number of client requests hitting the server every now and then, checking for new information.

Question 19

What are 2 ways of pulling data from Server over HTTP?

Answer 19

Triggering and event on the UI to send a request

Pulling dynamically at regular intervals without any human intervention (using AJAX)

Question 20

What is AJAX?

Answer 20

• Asynchronous JS and XML -
• Adds asynchronous behavior to web page.
• Polls server repeatedly every X unit of time
• On receipt of the data, the segment of the page is updated dynamically bye the callback method (without the page reloading)
• Uses XMLHttpRequest object to send requests

Question 21

What are Heartbeat Interceptors?

Answer 21

These are blank request responses between the client and server to prevent the browser from killing the connection.

Keeps the connection between client and server open

Question 22

What are websockets?

Answer 22

Persistent, bi-directional, low-latency data flow communication between client and server. Think of it as an ongoing conversation.

Can keep a client-server connection open as long as we want.

Runs over TCP, not HTTP. Server + Client should support web sockets.

Question 23

What are some use cases for websockets?

Answer 23

Use Cases: chat apps, real-time social streams, browser-based massive multiplayer games. Each use significant number of read writes compared to regular apps.

Question 24

WHat is AJAX - Long Polling?

Answer 24

Instead of immediately returning empty response, server holds the response until it finds an update to be sent to the client

Connection stays open longer compared to polling.

Can be used for simple a sync data fetch where you do not want to poll the server

Question 25

What are Server-Sent Events?

Answer 25

PUSH tech - Server automatically pushes data to client when updates are available. Incoming messages from server are treated as events.

Ideal for Real-time feeds (twitter), Stock Quotes in UI, Real time notifications.

Question 26

What are some benefits of Server sent events?

Answer 26

Cuts out large number of blank Request-Response cycles.
Reduces Bandwidth consumption

Question 27

How do Server Side events work?

Answer 27

Client establishes connection with initial request, then server initiates data transmission (Using HTML5 Event-Source API)

Server automatically pushes data to client when updates are available. Incoming messages from server are treated as events.

Question 28

Streaming over HTTP Use

Answer 28

Ideal for streaming extensive data over HTTP by breaking it into smaller chunks

Used for streaming multimedia content (large images, videos etc) over HTTP