Application Gateway

• Web traffic LB to distribute traffic to web applications
• Web Apps can reside in VM, VMSS or on-premise servers
• The Application Gateway is an OSI Layer 7 LB (At this layer the info is understandable, e.g., the path)
• Support for Secure Sockets Layer (SSL/TLS)
• Autoscaling can be enabled for the AG
• Web Application Firewall can be enabled for the AG
• Session Afinity can be enabled'
• An empty subnet is necessary for the AG

Components

• Frontend IP: access to the gateway
• Listener: Logical entity that checks for incomings requests. There can be multiple listeners
• Basic listener: listen to a single domain site
• Multi-site: listen and map to multiple domain sites
• Routing rules: Route traffic from the listener to the backend pool
• Basic routing rule: all requests to to the backend pool directly
• Path-based routing rule: requests are routed based on the URL of request
• Backend pools: NICs, VMSS, Public IP, Internal IP, SQDN, etc
• Health probes: Defines how the AG will monitor health of the resources in backend pool

Application Gateway vs. Load Balancer

• Load Balancer

• Simply redirects traffic to backend pool (machines)

• LB 4

• Application Gateway

• Redirects traffic to a specific backend pool based on routing rules (E.g., the path of the request /images, /videos)

• LB 7

OSI Model

1. Physical
2. Data Link
3. Network
4. Transport
5. Session
6. Presentation
7. Application