Notification System

Notification System is part 14 of 20 in the Low-Level Design path. Use this lesson to practice structured system design thinking and produce clear interview or architecture-review answers.

Where This Fits

• Parent path: System Design Learning Path
• Module: Low-Level Design
• Previous step: Splitwise
• Next step: URL Shortener LLD

Problem Framing

Before designing Notification System, clarify the goal, users, constraints, success metrics, and out-of-scope features. Good system design starts by reducing ambiguity before choosing technologies or patterns.

What You Should Design

Focus on classes, responsibilities, object relationships, APIs, and extensibility. A strong answer should include class diagrams, interfaces, entities, repositories, services, sequence flow, and test cases.

Functional Requirements

• Identify the primary actors and user journeys.
• Define the core operations the system must support.
• Clarify read-heavy, write-heavy, synchronous, and asynchronous flows.
• Define edge cases, validation rules, and failure behavior.

Non-Functional Requirements

• Scalability: expected users, requests, throughput, and growth path.
• Availability: uptime target, redundancy, failover, and recovery expectations.
• Performance: latency targets, throughput goals, and bottlenecks.
• Security: authentication, authorization, data protection, and audit needs.
• Maintainability: modularity, testability, observability, and operational ownership.

Design Approach

1. Start with requirements and assumptions.
2. Draw the high-level flow before deep implementation details.
3. Choose data models and storage based on access patterns.
4. Add caching, queues, partitioning, or replication only where the problem requires them.
5. Explain trade-offs and alternatives clearly.

Production Checklist

• Add metrics, logs, traces, alerts, and dashboards for critical flows.
• Define rate limits, retries, idempotency, and timeout behavior.
• Plan backup, restore, data retention, and disaster recovery.
• Protect sensitive data with encryption, access control, and audit trails.
• Document deployment, rollback, incident response, and ownership.

Interview Checkpoints

• Can you explain the design in five minutes before going deep?
• Can you defend your database and cache choices?
• Can you identify bottlenecks and scale them incrementally?
• Can you explain failure modes and recovery paths?
• Can you compare your design with at least one alternative?

Summary

Notification System is a design practice topic. Continue through the Low-Level Design sequence to build a clear, repeatable approach for system design interviews and production architecture discussions.