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
Network Attached Storage (NAS)
# 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
- More cost effective
- More reliable
- Can be accessed from any computer with an Internet connection.
- Web applications are updated more frequently than traditional software.
- Requires an internet connection
- Working in online application may lead to cyber attacks
- Documents shared in web applications may be accessed by unauthorised users.
- A webpage is a document that can be viewed in web browsers.
- 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.
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
- Operates without server connection
- Robust and reliable
- Used for powerful software applications
- 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.
- Easy and inexpensive to set up
- Easy to update and maintain the client systems
- Data is secured at a centralised location
- 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 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.
- 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
- 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
- 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