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InfrastructureApp Service · Azure SQL · Application Gateway01 / 10
Multi-Tier Web Application with Auto-Scaling
Highly available app tier behind Application Gateway
Overview
A highly available multi-tier architecture built on Azure App Services, Azure SQL Database, and Application Gateway. Traffic enters through the gateway, is load balanced across the web tier, and the data tier stays private to the application subnet. Auto-scale rules react to live CPU and request pressure so the platform absorbs traffic spikes without manual intervention, and Azure Monitor watches every tier for real-time alerting.
Engineering focus
Keeping the database tier unreachable from the internet while the web tier scales freely — health probes, private access paths, and scale rules all have to agree or the gateway drops the backend pool.
Architecture flow
🌐
User Traffic
Public internet
⚡
Application Gateway
WAF + path-based routing
🖥
Web Tier — App Service
Auto-scaled plan
🔧
App Tier — API
Private endpoint access
🗄
Azure SQL Database
No public endpoint
📊
Azure Monitor
Metrics · alerts · dashboards
Network security rules
| Rule | Direction | Source | Port | Purpose |
|---|---|---|---|---|
| Allow-HTTPS | Inbound | Internet | 443 | Public web access |
| Allow-Gateway | Inbound | App Gateway subnet | 443 | Backend pool traffic |
| Allow-SQL | Outbound | App subnet | 1433 | Database connectivity |
| Deny-All | Inbound | Any | Any | Default deny baseline |
Auto-scaling configuration
›Scale out: CPU > 70% for 5 minutes → add instance
›Scale in: CPU < 30% for 10 minutes → remove instance
›Minimum: 2 instances
›Maximum: 10 instances
Key outcomes
Highly available multi-tier design across App Services, Azure SQL, and Application Gateway
Auto-scaling and load balancing for dynamic traffic and consistent performance
Azure Monitor configured for real-time monitoring, alerting, and reliability
Stack
Azure App ServiceAzure SQLApplication GatewayAutoscaleAzure MonitorVNetNSG
Environment
RegionCanada Central
Resource Grouprg-multitier-prod
Entry PointApplication Gateway v2
Scale Range2 – 10 instances
Data TierAzure SQL (private)