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LLDsystem_design~12 mins

Sequence diagrams in LLD - Architecture Diagram

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System Overview - Sequence diagrams

A sequence diagram visually shows how different parts of a system talk to each other over time. It helps us understand the order of messages and actions between users, services, and databases in a simple, step-by-step way.

Architecture Diagram
User
  |
  v
API Gateway
  |
  v
Service Layer
  |
  v
Database
Components
User
actor
Initiates requests to the system
API Gateway
service
Receives user requests and routes them to appropriate services
Service Layer
service
Processes business logic and interacts with the database
Database
database
Stores and retrieves persistent data
Request Flow - 6 Hops
User → API Gateway
API Gateway → Service Layer
Service Layer → Database
Database → Service Layer
Service Layer → API Gateway
API Gateway → User
Failure Scenario
Component Fails:Database
Impact:Service Layer cannot retrieve or store data, causing request failures
Mitigation:Use database replication and fallback caches to serve read requests during failure
Architecture Quiz - 3 Questions
Test your understanding
Which component first receives the user's request in the sequence?
AService Layer
BAPI Gateway
CDatabase
DUser
Design Principle
Sequence diagrams help visualize the order of interactions between system parts, making it easier to understand and design clear communication flows.