System Overview - Notification system
This notification system sends messages to users through multiple channels like email, SMS, and push notifications. It must handle high volumes of notifications reliably and deliver them quickly.
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Notification system in LLD - Architecture Diagram
Architecture Diagram
User | v Load Balancer | v API Gateway | v Notification Service | | | v v v Email Service SMS Service Push Service | | | v v v Email Server SMS Gateway Push Server Database <-> Message Queue <-> Notification Service Cache <-> Notification Service
Components
User
client
Initiates notification requests
Load Balancer
load_balancer
Distributes incoming requests evenly to API Gateway instances
API Gateway
api_gateway
Handles client requests, routes them to Notification Service
Notification Service
service
Processes notification requests, decides delivery channels
Message Queue
queue
Buffers notification tasks for asynchronous processing
Email Service
service
Sends email notifications
SMS Service
service
Sends SMS notifications
Push Service
service
Sends push notifications
Email Server
external_service
Delivers emails to user inboxes
SMS Gateway
external_service
Delivers SMS messages to mobile networks
Push Server
external_service
Delivers push notifications to devices
Database
database
Stores user preferences and notification history
Cache
cache
Stores frequently accessed user data for quick retrieval
Request Flow - 18 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Notification Service
Notification Service → Cache
Cache → Notification Service
Notification Service → Database
Database → Notification Service
Notification Service → Message Queue
Message Queue → Email Service
Email Service → Email Server
Message Queue → SMS Service
SMS Service → SMS Gateway
Message Queue → Push Service
Push Service → Push Server
Notification Service → Database
Notification Service → API Gateway
API Gateway → Load Balancer
Load Balancer → User
Failure Scenario
Component Fails:Message Queue
Impact:Notification tasks cannot be buffered, causing delays or loss of notifications
Mitigation:Use queue replication and fallback to direct synchronous processing with rate limiting
Architecture Quiz - 3 Questions
Test your understanding
Which component is responsible for distributing incoming user requests evenly?
Design Principle
This design uses asynchronous processing with a message queue to handle high notification volumes reliably. Caching user preferences reduces database load and speeds up processing. Load balancing and API gateway ensure scalability and security.