Client Server Architecture:

Overview:-
Client-server is a computing architecture which separates a client from a server. Each client or server connected to a network can also be referred to as a node. The most basic type of client-server architecture employs only two types of nodes: clients and servers. This type of architecture is sometimes referred to as two-tier.
Each instance of the client software can send data requests to one or more connected servers. In turn, the servers can accept these requests, process them, and return the requested information to the client. Although this concept can be applied for a variety of reasons to many different kinds of applications, the architecture remains fundamentally the same.
These days, clients are most often web browsers. Servers typically include web servers, database servers and mail servers. Online gaming is usually client-server too.

Characteristics of a client:-
• Request sender is known as client
• Initiates requests
• Waits and receives replies.
• Usually connects to a small number of servers at one time
• Typically interacts directly with end-users using a graphical user interface

Characteristics of a server:-
• Receiver of request which is send by client
• Upon receipt of requests, processes them and then serves replies
• Usually accepts connections from a large number of clients
• Typically does not interact directly with end-users


The following are the examples of client/server architectures:-

1) Two tier architectures
In two tier client/server architectures, the user interface is placed at user's desktop environment and the database management system services are usually in a server that is a more powerful machine that provides services to the many clients. Information processing is split between the user system interface environment and the database management server environment. The database management server supports for stored procedures and triggers. Software vendors provide tools to simplify development of applications for the two tier client/server architecture.

2) Multi-tiered architecture
Some designs are more sophisticated and consist of three different kinds of nodes: clients, application servers which process data for the clients and database servers which store data for the application servers. This configuration is called three-tier architecture, and is the most commonly used type of client-server architecture. Designs that contain more than two tiers are referred to as multi-tiered or n-tiered.

The advantage of n-tiered architectures is that they are far more scalable, since they balance and distribute the processing load among multiple, often redundant, specialized server nodes. This in turn improves overall system performance and reliability, since more of the processing load can be accommodated simultaneously.

The disadvantages of n-tiered architectures include more load on the network itself, due to a greater amount of network traffic, more difficult to program and test than in two-tier architectures because more devices have to communicate in order to complete a client's request.

Advantages of client-server architecture:-
In most cases, client-server architecture enables the roles and responsibilities of a computing system to be distributed among several independent computers that are known to each other only through a network. This creates an additional advantage to this architecture: greater ease of maintenance. For example, it is possible to replace, repair, upgrade, or even relocate a server while its clients remain both unaware and unaffected by that change. This independence from change is also referred to as encapsulation.
All the data is stored on the servers, which generally have far greater security controls than most clients. Servers can better control access and resources, to guarantee that only those clients with the appropriate permissions may access and change data.
Since data storage is centralized, updates to those data are far easier to administer.
It functions with multiple different clients of different capabilities.

Disadvantages of client-server architecture :-
Traffic congestion on the network has been an issue since the inception of the client-server paradigm. As the number of simultaneous client requests to a given server increases, the server can become severely overloaded.
The client-server paradigm lacks the robustness. Under client-server, should a critical server fail, clients’ requests cannot be fulfilled.