Three-Tier Architecture

Architectural Patterns

The Three-Tier architecture is the foundational pattern for enterprise web applications, enforcing separation of concerns.

1. Presentation Tier (Client)

• Responsibility: Rendering UI and capturing user input. Client-side web APIs (MDN).
• Technologies: SPA Frameworks (React, Vue), Mobile SDKs (iOS, Android).
• State: Ideally stateless; maintains session via tokens (JWT) or cookies.
• Optimization: Assets served via CDN to minimize latency.

2. Application Tier (Logic)

• Responsibility: Business logic, authorization, data processing. What is Middleware? (Red Hat).
• Technologies: REST/GraphQL APIs (Node.js, Go, Python, Java).
• Scaling: Horizontal scaling behind a Load Balancer.
• Statelessness: Crucial for scaling. No local session storage; use external stores (Redis) or stateless tokens.

3. Data Tier (Persistence)

• Responsibility: Data storage and retrieval. Types of Databases (AWS).
• Technologies:
  • RDBMS: PostgreSQL, MySQL (ACID compliance).
  • NoSQL: MongoDB, DynamoDB (Flexible schema, high throughput).
  • Cache: Redis, Memcached (Sub-millisecond access).
• Scaling: Vertical (bigger instance) or Horizontal (Sharding/Read Replicas).

Microservices vs Monolith

• Monolith: All tiers in a single deployable unit. Simple to develop, hard to scale components independently.
• Microservices: Application tier broken into small, independent services communicating via gRPC/HTTP. Complex operations, high scalability.