System Overview - Notification system design
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.
0Notification system design in HLD - Architecture Diagram
Architecture Diagram
User | v Load Balancer | v API Gateway | v Notification Service | | | v v v Message Queue Cache User Preferences DB | | | v v v Email Service SMS Service Push Service | | | v v v SMTP Server SMS Gateway Push Notification Provider
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 and routes them to Notification Service
Notification Service
service
Processes notification requests and decides delivery channels
Message Queue
queue
Buffers notification tasks for asynchronous processing
Cache
cache
Stores recent notification statuses and user preferences for fast access
User Preferences DB
database
Stores user notification preferences and contact details
Email Service
service
Sends email notifications via SMTP Server
SMS Service
service
Sends SMS notifications via SMS Gateway
Push Service
service
Sends push notifications via Push Notification Provider
SMTP Server
external_service
Delivers emails to user mailboxes
SMS Gateway
external_service
Delivers SMS messages to mobile networks
Push Notification Provider
external_service
Delivers push notifications to user devices
Request Flow - 15 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Notification Service
Notification Service → Cache
Notification Service → User Preferences DB
Notification Service → Message Queue
Message Queue → Email Service
Email Service → SMTP Server
Message Queue → SMS Service
SMS Service → SMS Gateway
Message Queue → Push Service
Push Service → Push Notification Provider
Notification Service → Cache
Notification Service → API Gateway
API Gateway → User
Failure Scenario
Component Fails:Message Queue
Impact:Notification tasks cannot be queued, causing delays or loss of notifications
Mitigation:Use a replicated queue system with failover; buffer notifications temporarily in Notification Service memory
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.