Contains an internally resolvable FQDN or a private IP address, the application gateway routes the request to the backend server by using its instance private IP addresses.If there isn't a frontend public IP address, one is assigned for the outbound external connectivity. Is a public endpoint, the application gateway uses its frontend public IP to reach the server.This action maintains cookie-based session affinity, connection draining, host-name selection from the backend, and so on. When an application gateway sends the original request to the backend server, it honors any custom configuration made in the HTTP settings related to overriding the hostname, path, and protocol. The port and protocol used in HTTP settings determine whether the traffic between the application gateway and backend servers is encrypted (thus accomplishing end-to-end TLS) or is unencrypted. HTTP settings specify the protocol, port, and other routing-related settings that are required to establish a new session with the backend server. This load balances the requests on the servers.Īfter the application gateway determines the backend server, it opens a new TCP session with the backend server based on HTTP settings. If the backend pool contains multiple servers, the application gateway uses a round-robin algorithm to route the requests between healthy servers. The health of the server is determined by a health probe. When the application gateway selects the backend pool, it sends the request to one of the healthy backend servers in the pool (y.y.y.y). Rules are processed in the order they're listed in the portal for v1 SKU. This action determines which backend pool to route the request to.īased on the request routing rule, the application gateway determines whether to route all requests on the listener to a specific backend pool, route requests to different backend pools based on the URL path, or redirect requests to another port or external site. If a request is valid and not blocked by WAF, the application gateway evaluates the request routing rule that's associated with the listener. How an application gateway routes a request Therefore, internal load-balancers can only route requests from clients with access to a virtual network for the application gateway. If you're using a Custom or Private DNS zone, the domain name should be internally resolvable to the private IP address of the Application Gateway. Internal application gateways use only private IP addresses. As a result, internet-facing application gateways can route client requests from the internet. The DNS name of an internet-facing application gateway is publicly resolvable to its public IP address. An internet-facing application gateway uses public IP addresses. If it's in Detection mode, the request is evaluated and logged, but still forwarded to the backend server.Īzure Application Gateway can be used as an internal application load balancer or as an internet-facing application load balancer. If the request isn't valid and WAF is in Prevention mode, it's blocked as a security threat. If the request is valid, it's routed to the backend. This action determines if the request is valid request or a security threat. If a web application firewall (WAF) is in use, the application gateway checks the request headers and the body, if present, against WAF rules. It's configured with a frontend IP address, protocol, and port number for connections from clients to the application gateway. A listener is a logical entity that checks for connection requests. The application gateway accepts incoming traffic on one or more listeners. The Azure DNS returns the IP address to the client, which is the frontend IP address of the application gateway. Azure controls the DNS entry because all application gateways are in the domain. How an application gateway accepts a requestīefore a client sends a request to an application gateway, it resolves the domain name of the application gateway by using a Domain Name System (DNS) server. This article explains how an application gateway accepts incoming requests and routes them to the backend.
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