🚀 Azure Application Gateway: Smart Load Balancing & Security

Ensuring high availability and efficient load balancing is crucial for web applications. Azure offers several traffic management solutions, including Application Gateway, Front Door, Load Balancer, and Traffic Manager. Today, let's focus on why Application Gateway stands out as a powerful tool for managing web traffic.

🚀 Why we should use Azure Application Gateway?

🔹 Layer 7 Load Balancing: Unlike Layer 3 or 4 solutions, Application Gateway makes intelligent routing decisions based on HTTP request properties. For example, requests to /images/ can be directed to dedicated image servers, while /videos/ traffic is routed to specialized video servers.

🔹 SSL/TLS Termination (Offloading): Reduces processing load on backend servers by decrypting traffic at the gateway before forwarding it unencrypted. 

Note: This might conflict with compliance requirements, so verify your app’s security needs !!

🔹 Autoscaling: Dynamically scales up or down based on traffic patterns, ensuring cost-effective resource utilization.

🔹 Zone Redundancy: Operates across multiple Availability Zones, enhancing fault tolerance without needing separate gateways in each zone.

🔹 Web Application Firewall (WAF): Provides centralized security against common exploits like SQL injection and cross-site scripting (XSS). Built on OWASP 3.1 (WAF_v2), it can function in Detection Mode (alerting admins) or Prevention Mode (blocking threats proactively).

🔹 URL-Based Routing: Enables smart traffic distribution by directing different types of content to the most appropriate backend pools. Example: http://contoso.com/video/* → VideoServerPool

🔹 Multiple-Site Hosting: Hosts multiple web applications on a single gateway, routing requests based on hostname or domain. Example: http://contoso.com → ContosoServerPool

🔹 Redirection & Rewrite Capabilities: 

✔ Redirect HTTP → HTTPS to enforce encrypted traffic. 
✔ Rewrite HTTP headers & URLs to enhance security (e.g., add HSTS or remove sensitive response headers).

🔹 Cookie-Based Session Affinity: Ensures users maintain session continuity by always connecting to the same backend server. Useful when session state is stored locally.

⚙️ How to Deploy & Configure Azure Application Gateway ⚙️

✅ Dedicated Subnet: Create a subnet (e.g., myAGSubnet) within a Virtual Network. 
✅ Frontend IP: Define whether to use a public or private IP or both (If you configured multiple listeners) to receive client requests. 
✅ Backend Pool: Assign backend servers via NICs, Virtual Machine Scale Sets, public/internal IPs, or FQDNs. 
✅ HTTP/HTTPS Listener: Specify which port (e.g., 80, 443) will handle incoming requests. 
✅ Routing Rules: Set up domain-based (host-based routing) or path-based routing logic. 

🔹 Host-Based Routing means routing traffic based on the hostname in the HTTP request header 
🔹 Path-based Routing allows you to direct traffic to different backend pools based on the URL path in the request.

✅ Health Probes: Ensure backend servers are online using TCP or HTTP-based monitoring.