Proxy pattern in LLD - Architecture Diagram

System Overview - Proxy pattern

The Proxy pattern provides a placeholder or surrogate for another object to control access to it. It is used to add additional functionality like access control, lazy loading, or logging without changing the original object's code.

Key requirements include controlling access to the real object, possibly delaying its creation, and adding extra behavior transparently.

Architecture Diagram

User
  |
  v
Proxy
  |
  v
Real Subject
  |
  v
Resource

Components

User

client

Initiates requests to access the resource

Proxy

proxy

Controls access to the Real Subject, adds extra behavior like access control or caching

Real Subject

service

The actual object that performs the core operations

Resource

resource

Underlying data or service used by the Real Subject

Request Flow - 7 Hops

User → Proxy

Proxy → Proxy

Proxy → Real Subject

Real Subject → Resource

Resource → Real Subject

Real Subject → Proxy

Proxy → User

Failure Scenario

Component Fails:Proxy

Impact:User requests cannot be processed or access control fails, potentially exposing Real Subject directly or blocking access

Mitigation:Implement fallback mechanisms or redundant proxies; ensure Real Subject has its own access controls

Architecture Quiz - 3 Questions

What is the main role of the Proxy in the Proxy pattern?

A To store the underlying resource data

B To replace the User in sending requests

C To control access to the Real Subject and add extra behavior

D To directly process all user requests without forwarding

Design Principle

The Proxy pattern demonstrates how to add a control layer between a client and a service to manage access, add caching, or delay expensive operations, improving modularity and flexibility without changing the core service.