Chain of Responsibility pattern in LLD - Architecture Diagram

System Overview - Chain of Responsibility pattern

The Chain of Responsibility pattern allows a request to pass through a chain of handlers. Each handler decides to process the request or pass it to the next handler. This design helps separate concerns and makes the system flexible to add or change handlers without modifying the client.

Architecture Diagram

User
  |
  v
Handler 1 ---> Handler 2 ---> Handler 3 ---> Null Handler
  |
Response

Components

User

client

Initiates the request to be handled

Handler 1

handler

First handler in the chain; processes or forwards request

Handler 2

handler

Second handler; processes or forwards request

Handler 3

handler

Third handler; processes or forwards request

Null Handler

handler

End of chain; handles unprocessed requests or returns default response

Request Flow - 8 Hops

User → Handler 1

Handler 1 → Handler 1

Handler 1 → Handler 2

Handler 2 → Handler 2

Handler 2 → Handler 3

Handler 3 → Handler 3

Handler 3 → Null Handler

Null Handler → User

Failure Scenario

Component Fails:Handler 2

Impact:Requests that require Handler 2's processing are not handled and passed down the chain, possibly causing delays or incorrect handling.

Mitigation:Implement fallback logic in Handler 3 or Null Handler to handle requests if Handler 2 fails; monitor handler health and remove or restart failing handler.

Architecture Quiz - 3 Questions

What happens if Handler 1 cannot process a request?

A It forwards the request to Handler 2

B It returns an error to the user

C It processes the request anyway

D It stops the request chain

Design Principle

The Chain of Responsibility pattern decouples sender and receiver by passing requests along a chain of handlers. This allows flexible and dynamic handling of requests without tight coupling, improving maintainability and scalability.