Design a Resilient 3-Tier Web Architecture on AWS
A high-availability 3-tier architecture isolates public traffic at edge load balancers, scales stateless compute dynamically across availability zones, and safeguards relational data with automated replication.
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Loading AWS 3-Tier Cloud Blueprint...
Mounting vector diagram elements, nodes, and capacity metrics
1. Problem & Challenge
An enterprise web platform experiences unpredictable traffic spikes. It requires zero-downtime rolling updates, sub-20ms response times, cross-AZ fault tolerance, and secure isolation between public web traffic, business logic, and database persistence.
2. Core Building Blocks & Responsibilities
👉 Desliza la tabla para ver roles y responsabilidades| Component | Role | Plain-English Explanation |
|---|---|---|
| Route 53 & CloudFront CDN | Global DNS & Edge Caching | Routes visitors to the closest edge point of presence and caches static assets to eliminate origin latency. |
| Application Load Balancer (ALB) | Public Ingress & WAF | Terminates TLS, runs AWS WAF inspection rules, and performs path-based routing across target groups. |
| EC2 Auto Scaling Group (ASG) | Private Stateless Compute | Runs microservices across multiple Availability Zones, automatically scaling instances based on CPU and request latency metrics. |
| ElastiCache Redis | In-Memory Caching & Session Store | Caches hot database queries and user session states in sub-millisecond RAM. |
| Multi-AZ RDS PostgreSQL | ACID Persistence & Standby Replica | Handles read/write transactions with synchronous replication to a hot standby in another AZ for instant automated failover. |
| Amazon S3 & CloudWatch | Object Storage & Central Telemetry | Stores static media with 99.999999999% durability while CloudWatch collects metrics and alarms. |
3. Step-by-Step Request Flow
Edge Resolution & Asset Delivery
DNS resolves via Route 53. Static media is served directly from CloudFront edge caches.
Public Ingress & TLS Termination
Dynamic API calls hit ALB across public subnets, passing through AWS WAF security inspection.
Stateless Microservice Processing
ALB dispatches traffic to healthy EC2 instances across private subnets spanning 2+ Availability Zones.
Cache-Aside Querying
Compute layer checks ElastiCache Redis. On cache hit, response returns immediately; on miss, queries RDS and repopulates Redis.
Synchronous Standby Replication
State mutations write to RDS Primary with synchronous replication to the hot standby replica before returning 200 OK.
4. Architectural Trade-offs
Multi-AZ RDS vs Aurora Multi-Master
Chosen: Multi-AZ RDS Standby
Rationale: Multi-AZ RDS provides simple, battle-tested automated failover without the complex conflict-resolution semantics and higher cost of multi-master write topologies.
Stateless Auto Scaling vs Sticky Sessions
Chosen: Stateless Compute with Central Redis
Rationale: Sticky sessions degrade load balancer distribution and cause session loss when instances terminate. Offloading sessions to ElastiCache allows instances to scale to zero gracefully.
Interview Tip
Emphasize Defense in Depth: Never place database instances in public subnets. Detail security group chaining where the RDS security group ONLY accepts port 5432 ingress from the EC2 application security group, preventing direct internet exposure.
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