Client-Server Model

Client: The entity that initiates requests.

• General Term: It simply refers to the entity making requests in the client-server model.
• Often thought of as an end user using devices like a desktop or laptop with a browser, but this is not strictly necessary.
• Flexibility in Role: The client can also be another server, indicating that the role is not limited to just user-end devices but can be any entity that needs to fetch data or services from another server.
• Example(Servers act as clients to other servers.):
  • Google.com might use a third-party service hosted on another server. In this case, Google's server acts as a client to the third-party server.

Server: The entity that responds to requests.

• Typically not an end-user machine but a powerful computer/ a cluster of computers located in a data center
• Responsibilities: Accepts and processes requests from clients.

Remote Procedure Calls (RPCs)

• RPC: Stands for Remote Procedure Call
  • Enables code execution on a remote server, mimicking local function calls
  • Used for communication between machines over a network
  • Essential for executing server-side code from a client
  • RPC underlies many application layer protocols, including HTTP and WebSocket.

HTTP (HyperText Transfer Protocol)

• HTTP is an application layer protocol built on top of IP and TCP.
• It is used for transmitting data over the web.
• Request-Response Protocol:
  • Client makes a request.
  • Server processes the request and sends a response.

Two Components of an HTTP Request: headers and body

Headers:

Contain metadata about the request.

• General Headers: Basic information applicable to both request and response (e.g., URL, connection status).

  

• Request Headers: Specific information set by the client (e.g., method, path, user-agent). These headers indicate which URL the client wishes to access and the path used for the request.