Software Engineering basics - Client–Server Model

Client–Server Model

Definition:
The Client–Server Model is a distributed system architecture in which tasks or workloads are divided between two types of entities:

• Clients — the users or front-end systems that request services.

• Servers — the back-end systems that provide and manage those services.

In this model, the client sends a request to the server, and the server processes it and returns a response.

Key Idea

• Client: Requests data or services (e.g., a web browser).

• Server: Provides the requested data or service (e.g., a web server).

• Communication happens over a network, usually using standard protocols such as HTTP, FTP, or SMTP.

Diagram of the Client–Server Model

           +-----------------------+
           |       Client 1        |
           | (e.g., Web Browser)   |
           +-----------+-----------+
                       |
                       |  Request (e.g., HTTP Request)
                       v
           +-----------+-----------+
           |         SERVER         |
           | (e.g., Web Server)     |
           +-----------+-----------+
                       ^
                       |  Response (e.g., Web Page, Data)
                       |
           +-----------------------+
           |       Client 2        |
           | (e.g., Mobile App)    |
           +-----------------------+

In larger systems, there can be multiple clients and servers communicating over a network.

Working of the Client–Server Model

1. Client Request:
   The client (e.g., browser, app) sends a request to the server — such as asking for a web page or data.

2. Server Processing:
   The server receives the request, processes it (e.g., queries a database, performs calculations), and prepares a response.

3. Response Sent Back:
   The server sends the response (e.g., an HTML page or JSON data) back to the client.

4. Display to User:
   The client interprets the response and displays it to the user.

Example

Web Application Example:

• Client: Web browser (like Chrome)

• Server: Web server (like Apache or Nginx)

• Process:

  1. The browser sends an HTTP request for www.example.com.

  2. The server retrieves the web page from storage and sends it back.

  3. The browser displays the page to the user.

Advantages of the Client–Server Model

1. Centralized Data Management:
   Servers manage all data, making maintenance and updates easier.

2. Resource Sharing:
   Multiple clients can share the same server resources.

3. Scalability:
   New clients can be added easily without changing the server’s structure.

4. Security:
   Data is stored centrally, allowing better control and monitoring.

5. Maintenance Efficiency:
   Updates and configurations are applied only on the server side.

Disadvantages of the Client–Server Model

1. Server Overload:
   Too many client requests can overwhelm the server.

2. Single Point of Failure:
   If the server goes down, clients cannot access services.

3. Network Dependency:
   The system heavily relies on network connectivity and speed.

4. Cost:
   High-performance servers and maintenance can be expensive.

In Summary