Three-tier web application architecture on AWS separates presentation, application logic, and data storage across isolated network layers within a VPC. Users connect through an Application Load Balancer that distributes traffic to an Auto Scaling Group of three EC2 t3.medium instances in a Private Subnet - App Tier. Application servers read from RDS PostgreSQL Read Replica and write to RDS PostgreSQL Primary in a Private Subnet - Data Tier, while serving static content from an S3 Bucket. This architecture delivers high availability, horizontal scalability, and fault isolation for production web workloads. Fork this diagram on Diagrams.so to customize instance types, add CloudFront CDN, or integrate ElastiCache for session management.