Cloud Computing And Web Applications

Client-to-server network model

• Clients are computers that request information

• Servers are computers that provide information

• A client depends on the server for information

• For example, the client-side of a web application is a web browser. The web server provides the information.

Types of servers

• Web servers

• Application servers

• Network Attached Storage (NAS)

• Print servers

• Mail servers

• etc

Peer-to-peer model

• In a P2P network, each and every computer in a network is responsible for providing data equally.

• Each computer can provide data requested by other computers in the network.

• At the same time, any computer can request data from any computer.

• This type of network is not suitable for systems where there is a single source of truth (ie, databases, online ticketing systems etc)

• Due to a lack of servers, this type of network may lead to difficulty in storing backups.

• Known best for file sharing

Cloud Computing

• The use of hardware and software to deliver a service over a network such as the internet is called cloud computing.
• A webpage displays these services to a client

Traditional computing vs cloud computing

Traditional computing

• Files are stored in the hard drive of a computer and processed using the same computer.

Cloud computing

• Files are stored online and processed using services that are available online.

Pros and Cons

Pros

• More cost effective
• More reliable
• Can be accessed from any computer with an Internet connection.
• Web applications are updated more frequently than traditional software.

Cons

• Requires an internet connection
• Working in online application may lead to cyber attacks
• Documents shared in web applications may be accessed by unauthorised users.

Webpages

• A webpage is a document that can be viewed in web browsers.

Back-end/server-side

• A server-side script is processed on the server when a user requests information
• The processed script returns the result to the user’s request
• Widely used in websites and apps that store a large amount of information
• SQL, PHP, Python, Ruby, Java and many more are used as backend languages
• The validation of data is also carried out on the server-side by comparing the data entered by the user with the existing data in the server.
• Hackers may try to enter malicious JavaScript in the front-end.

Functions of server-side processing are:

• Processing client’s queries
• Provides data security
• Encryption of data
• Updating server database

Application Programming Interface (API)

• API is a set of protocols that governs how two applications interact with each other

• Websites often embed functions such as maps, spreadsheets etc

• Websites typically do not create these functions independently

• Instead, an API is used to include these functionalities within a website

• For example, Google has an API, which various websites use to include their address in the “contact us” menu

• A web application that uses API from various sources is called a mashup.

• API also defines the protocols that will be used in the web service.

• An example of such a protocol is a WebSocket which creates a connection between two computers

  • It provides a bidirectional communication channel between client and webserver over a single line.

WebSocket protocol

• Firstly, the client sends a handshake request

• Then, the server responds with a bidirectional channel on a single socket

• Both client and server can send messages to each other simultaneously. In HTTP, the webpage need not be refreshed. The connection closes when one of them ends it.

• The packets are also accepted without the usual security checks. As a result, this protocol helps us achieve fast and real-time communication.

• This is widely used in online gaming and instant communication.

• When this protocol is used, fewer webservers are required, saving transmission time, bandwidth, cost of hardware and cost of mobile communication.

Thick vs thin client computing

• The term thickness refers to the independent processing and storage of a client in a client-server model.

Thick client

• A thick client processes most of its data and requires little help from the server

Pros

• Operates without server connection
• Robust and reliable
• Used for powerful software applications

Cons

• Expensive to install as it requires highly specialised computers at the client side.
• Software has to be installed at each client computer and maintained regularly.
• Data is distributed, so data integrity issues may arise.

Thin client

• A thin client is highly dependent on the server for data processing and storage
• Without a server, the functionality of a thin client will be affected
• The thinnest client that requires a server for most of its operations will only require minimum processing power and no storage.
• This type of client system is often referred to as a dumb terminal.

Pros

• Easy and inexpensive to set up
• Easy to update and maintain the client systems
• Data is secured at a centralised location

Cons

• Client computers are affected when a server malfunctions
• Setting up a highly efficient server is expensive
• Highly reliable network connections are required
• When the number of client computers increased, the performance of this model may be affected

CRUD

• CRUD stands for Create, Retrieve, Update, Delete
• CRUD explains the main functions of a database. Without the four functions denoted by CRUD, it is not possible to have a complete database.
• It also specifies how data is obtained and presented to the user.

REST

• Representational State Transfer
• REST is a system design concept in which the HTTP request methods are used to interact with a database server through a webserver.
• The client does not know how the data is received and processed by the database.
• In this type of system, client and server systems can be developed independently.

JSON and XML

• JSON and XML are methods used to format data objects transferred across servers and web applications.
• When a user places a GET request, the values in the table are returned

JSON

• Based on objects and values, easy to read
• Less number of lines of code generated
• The syntax is simpler
• Arrays are supported
• Data is clearly defined and easier to parse
• Due to limited number of data types, JSON is not suitable for all applications

XML

• Use markup tags to make it comparatively easier to read
• Comparatively more lines of code
• Complicated syntax, harder to make
• Data is extracted from tags, harder to parse
• Wide range of available data types

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