Architecture of Network Applications

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Client Server Architecture

Client-server refers to a relationship between cooperating programs in an application, with clients initiating service requests and servers providing that function or service. Let us first become familiar with some terminology before discussing Client-Server architecture! We assure you that there are very few!

What is a Client?

A client could be a program that runs on a local machine and requests services from a server. The user or another application program launches a client program, which terminates when the service is completed. It could also be hardware.

What is a Server?

A server runs services that may be required by other computers. It could be a file server, database server, home media server, print server, or web server, depending on the service that is running. A server can sometimes be a program that runs on a remote machine and provides services to clients. When it starts, it opens the door for incoming client requests, but it never initiates a service unless specifically requested to do so.

A server could be any type of device/service that can share and store data. Servers can store and process information on their own systems as well as request it from others. Servers began as small devices that simply transferred data to a more functional computer, and have since grown in size and capability to perform more complex functions. Virtual servers are now available on internet-accessible cloud computing platforms.

To put it simply, A server is a computer or system that manages network access to a centralized resource or service. Servers can store and manage files, host websites and applications, and run databases, among other things. They are often connected to clients, which are the devices or systems that request access to the server’s services. Servers can be physical hardware or virtualized software instances that run on a computer or in the cloud.

There are many different types of servers, each designed to perform specific functions. Some examples include:

File servers store and manage files that can be accessed by users or other systems over a network.

Application servers: These servers host and manage application software and provide access to those applications over a network.

Web servers host and deliver web pages and other content through the internet.

Database servers store and manage large amounts of data, and provide access to that data through a structured query language (SQL).

Game servers provide multiplayer capability for video games and other interactive experiences.

Virtualization servers create virtual instances of servers and networks, allowing multiple servers to run on a single physical machine.

Mail servers handle the sending and receiving of email messages.

DNS servers translate domain names into IP addresses, allowing users to connect to websites and other services using human-readable names.

VPN servers allow secure connections to be made to a private network over the internet.

And many more………..

It’s worth noting that some servers can perform multiple functions, and many servers are built using specialized software, such as LAMP, WAMP, XAMPP, and so on which are the combination of different software that run on the server.

What Is The Difference Between An Application Server And A Web Server?

An application server and a web server are both types of servers, but they have different roles and responsibilities.

A web server is responsible for handling incoming HTTP requests and returning HTTP responses. It is primarily responsible for serving static content such as HTML, CSS, and JavaScript files, as well as images and other multimedia files. Examples of web servers include Apache HTTP Server, Microsoft IIS, and Nginx. 

Don’t be concerned if you’re unfamiliar with the terms. We’re only getting started. We’re preparing the groundwork. In subsequent tutorials, we will go over these terms in great detail.

An application server, on the other hand, is responsible for running business logic and providing access to backend resources such as databases. It can handle dynamic content generated by the application, and it can also handle security, scalability, reliability, and other operational concerns. Application servers are designed to host enterprise-level applications and services, and they often provide additional features such as connection pooling, caching, and load balancing. Examples of application servers include Oracle WebLogic, IBM WebSphere, and Red Hat JBoss.

In practice, web servers and application servers can be used together to handle different aspects of a web application. The web server handles the incoming HTTP requests and routes them to the appropriate application server, which then handles the business logic and returns the response back to the web server, which sends it back to the client. This separation of concerns allows for better scalability, security, and performance.

It’s worth noting that some servers like the Apache Tomcat, can work as both web server and application server, where it can handle both static and dynamic content, and it can also handle the business logic and backend resources.

What is a Host?

A host is a computer that is connected to other computers and provides data or services over a network. In theory, every computer connected to a network serves as a host to other network peers. A host, in essence, represents the logical relationship between two or more computers on a network.

Let’s say you want to download an image from another computer on your network. Because that computer is “hosting” the image, it is the host computer. If that same computer, on the other hand, downloads an image from your computer, your computer becomes the host computer.

Other computers can use your computer as a host. Similarly, your router can act as a host for other routers. A host must have an assigned IP address. As a consequence, modems, hubs, and switches are not considered hosts because they lack IP addresses.

What Is The Difference Between A Server And A Host?

A Server

    Can be a physical device or software program

    Installed on a host computer

    Provides specific services

    Serves only clients

A Host

    Is always a physical computer or device

    Can run both server and client programs

    Provides specific services

    Serves multiple users and devices

The Client/Server Model

The client/server model is used in the majority of modern network programming. A client/server application typically stores large amounts of data on an expensive, high-powered server or cloud of servers, while client software running on relatively inexpensive personal computers handles the majority of the program logic and the user interface.

There is an always-on host called the server in a client-server architecture that services requests from many other hosts called clients.

In most cases, a server sends data while a client receives it; however, it is uncommon for one program to send or receive data exclusively. A more trustworthy distinction is that a client initiates a conversation, whereas a server waits for clients to initiate conversations with it. The diagram below depicts both possibilities. In some cases, a single program can function as both a client and a server.

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Note that clients do not directly communicate with each other in the client-server architecture, for example, two browsers do not directly communicate in the Web application. Another feature of the client-server architecture is that the server has a fixed, well-known address known as an IP address (which we’ll go over shortly). A client can always contact the server by sending a packet to the server’s IP address because the server has a fixed, well-known address and is always on.

Many examples of client/server systems are already familiar to you. The Web will be the most popular client/server system on the Internet in 2023. Web servers, such as Apache, respond to requests from web browsers such as Brave. Data is stored on the web server and delivered to clients who request it. Except for the initial page request, almost all data is transferred from the server to the client rather than from the client to the server. FTP is an older service that adheres to the client/server paradigm.

FTP employs various application protocols and software, but it is still divided into FTP servers that send files and FTP clients that receive files. People frequently use FTP to upload files from the client to the server, making it more difficult to claim that data transfer is primarily one-way, but it remains true that an FTP client initiates the connection and the FTP server responds.

A single-server host is frequently incapable of handling all client requests in a client-server application. A popular social-networking site, for example, can quickly become overwhelmed if only one server handles all of its requests. As a consequence, a data center with a large number of hosts is frequently used to create a powerful virtual server.

Search engines (e.g., Google and Bing), Internet commerce (e.g., Amazon and Alibaba), Web-based email (e.g., Gmail), and social networking (e.g. Facebook and Instagram) all use one or more data centers.  In total, Google has nearly 30 owned data centers either in operation or under development across 10 countries throughout the world that handle search, YouTube, Gmail, and other services. Hundreds of thousands of servers in a data center must be powered and maintained. Furthermore, service providers must pay recurring interconnection and bandwidth costs for data transmission from their data centers.

Peer To Peer Architecture

Not all applications are easily fitted to a client/server architecture. In networked games, for example, it appears likely that both players will send data back and forth roughly equally (at least in a fair game). Peer-to-peer connections are what they’re called. A peer-to-peer network is best illustrated by the telephone system. Each phone has the ability to call or be called by another phone. You do not need to purchase two phones to make and receive calls.

In a peer-to-peer (P2P) architecture, each device or application acts as both a client and a server, allowing them to share resources and communicate directly with each other. This architecture does not rely on a central server or authority to manage the network or control the flow of data. Instead, each device is responsible for maintaining its own resources and communicating with other devices on the network. The peers are not owned by the service provider, but rather are user-controlled desktops and laptops, with the majority of the peers residing in homes, universities, and offices. The architecture is known as peer-to-peer because the peers communicate without the use of a dedicated server.

Some of the key features of P2P networks are:

  • Decentralized: P2P networks do not rely on a central server or authority to manage the network or control the flow of data. This makes the network more resilient to failures and outages.
  • Self-Organizing: P2P networks are self-organizing, meaning that each device is responsible for joining and leaving the network, and for maintaining its own resources. This makes the network more flexible and adaptable.
  • Resource Sharing: P2P networks allow devices to share resources, such as files, processing power, and storage, with other devices on the network. This allows the network to be more efficient and scalable.
  • Direct Communication: P2P networks allow devices to communicate directly with each other, rather than relying on a central server or intermediary. This allows the network to be more responsive and reduces latency.

Examples of P2P networks include file sharing networks like BitTorrent, instant messaging networks like Jabber, and distributed systems like Ethereum. P2P networks are often used for applications that require distributed control, scalability, and fault tolerance.

It is worth mentioning that P2P networks can have security, privacy, and scalability issues, particularly if the network is not properly designed and managed. Furthermore, some P2P networks may employ a hybrid architecture, which combines aspects of P2P with other network architectures, such as client-server.

Java’s core networking API does not support explicit peer-to-peer communication. However, applications can easily provide peer-to-peer communications in a variety of ways, the most common of which is by acting as both a server and a client. Alternatively, the peers can communicate with one another via an intermediary server program that relays data from one peer to the other. This neatly solves the problem of how two peers discover each other.

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