This diagram explains a classic 3-tier web architecture, a fundamental pattern for building robust and scalable applications. This implementation is deployed on AWS and automated with CloudFormation.
Figure 1: A standard 3-tier architecture on AWS. Click the image to view full size.
Architectural Overview
The 3-tier architecture separates the application into three logical and physical layers:
- Presentation Layer (Web Tier): This is the layer that users interact with. It includes a load balancer that distributes traffic and web servers that serve the user interface. This layer lives in a public subnet, making it accessible from the internet.
- Application Layer (App Tier): This layer contains the business logic of the application. It runs on application servers (like EC2 instances) in a private subnet. It is not directly accessible from the internet, which enhances security.
- Data Layer (Database Tier): This layer stores the application's data. It consists of a database (like Amazon RDS) in a separate, private subnet, making it the most secure part of the architecture.
Why This Architecture?
This design is a standard for building enterprise-level applications for several reasons:
- Security: By placing the application and database layers in private subnets, you protect them from direct internet access, significantly reducing the attack surface.
- Scalability: Each layer can be scaled independently. If your application logic becomes a bottleneck, you can add more application servers without touching the other layers.
- Maintainability: The separation of concerns makes the application easier to develop, update, and maintain. Different teams can work on different layers simultaneously.
- Automation: Using AWS CloudFormation to define this infrastructure as code allows for fast, reliable, and repeatable deployments, eliminating manual configuration errors.