Azure 3-Tier Web Architecture

What this diagram shows

A three-layer Azure deployment where incoming traffic passes through Front Door for global distribution and DDoS protection, then through an Application Gateway for routing and SSL termination within a Virtual Network. App Service instances run the application logic, connecting to Azure SQL Database for relational data and Azure Cache for Redis for session state and frequently accessed data. This architecture separates presentation, application, and data concerns across managed Azure services within a secure perimeter.

Key components

• Azure Front Door — Global load balancer and content delivery network that routes user traffic to the nearest backend region and provides DDoS protection at the edge.
• Application Gateway — Layer 7 load balancer within the VNet that performs request routing, SSL/TLS termination, and URL-based path routing across App Service instances.
• App Service — Managed compute service hosting the application code, automatically scaled based on demand and integrated with VNet via service endpoints or private endpoints.
• Azure SQL Database — Fully managed relational database providing ACID compliance, automated backups, and built-in security for application data persistence.
• Azure Cache for Redis — In-memory data store used for distributed caching, session management, and real-time data access to reduce database load.
• Virtual Network — Isolated network boundary that contains Application Gateway, App Service, and optionally database resources for network segmentation and private connectivity.

When to use it

Use this diagram when designing stateless web applications requiring global reach, scalability, and adherence to defence-in-depth security. It suits e-commerce platforms, SaaS applications, and multi-region services where you need automatic failover, regional routing, and separation of presentation from application and data tiers. Choose this when your team is committed to Azure services and wants managed infrastructure without container orchestration overhead.

Common mistakes

• Placing the database outside the VNet, exposing it to the public internet instead of restricting access to App Service instances through private endpoints or firewall rules.
• Treating Front Door and Application Gateway as interchangeable or omitting Front Door entirely when global traffic distribution and DDoS mitigation are required for public-facing services.
• Assuming Redis is mandatory for all architectures; add it only when session persistence, high-frequency reads, or real-time data justify the operational overhead and cost.

Adapting it to your system

Replace App Service with Azure Container Instances or AKS if your workload requires custom container images or orchestration. Substitute Azure SQL Database with Cosmos DB for non-relational data or when multi-region write capability is needed. Add a separate admin subnet with a Bastion host if you need secure management access. Remove Front Door if your service is region-specific or behind a corporate network. Introduce Azure KeyVault for secret and certificate management, and attach Application Insights to all tiers for observability.