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Listeners ​

Configure listeners ​

A listener is a logical entity that checks for incoming connection requests by using the port, protocol, host, and IP address. When you configure a listener, you must enter values that match the corresponding values in the incoming request on the gateway.

When you create an application gateway by using the Azure portal, you also create a default listener by choosing the protocol and port for the listener. You can choose whether to enable HTTP2 support on the listener. After you create the application gateway, you can edit the settings of that default listener (appGatewayHttpListener) or create new listeners.

app-gateway-error-codes

Listener type ​

When you create a new listener, you must choose between basic and multi-site.

  • Basic: All requests for any domain will be accepted and forwarded to backend pools.
  • Multi-site: Forward requests to different backend pools based on the host header or host names. You must specify a host name that matches with the incoming request. This is because Application Gateway relies on HTTP 1.1 host headers to host more than one website on the same public IP address and port.

Order of processing listeners ​

For the v1 SKU, requests are matched according to the order of the rules and the type of listener. If a rule with basic listener comes first in the order, it's processed first and accepts any request for that port and IP combination. To avoid this, configure the rules with multi-site listeners first and push the rule with the basic listener to the last in the list.

For the v2 SKU, multi-site listeners are processed before basic listeners.

Front-end IP address ​

Choose the front-end IP address that you plan to associate with this listener. The listener will listen to incoming requests on this IP.

Front-end port ​

Choose the front-end port. Select an existing port or create a new one. Choose any value from the allowed range of ports. You can use not only well-known ports, such as 80 and 443, but any allowed custom port that's suitable. A port can be used for public-facing listeners or private-facing listeners.

Protocol ​

Choose HTTP or HTTPS:

  • HTTP: traffic between the client and the application gateway is unencrypted.
  • HTTPS: enables TLS termination or end-to-end TLS encryption. The TLS connection terminates at the application gateway. Traffic between the client and the application gateway is encrypted. If you want end-to-end TLS encryption, you must choose HTTPS and configure the back-end HTTP setting. This ensures that traffic is re-encrypted when it travels from the application gateway to the back end.

To configure TLS termination and end-to-end TLS encryption, you must add a certificate to the listener to enable the application gateway to derive a symmetric key. The symmetric key is used to encrypt and decrypt the traffic that's sent to the gateway. The gateway certificate must be in Personal Information Exchange (PFX) format. This format lets you export the private key that the gateway uses to encrypt and decrypt traffic.

Redirection overview ​

You can use application gateway to redirect traffic. It has a generic redirection mechanism which allows for redirecting traffic received at one listener to another listener or to an external site. This simplifies application configuration, optimizes the resource usage, and supports new redirection scenarios including global and path-based redirection.

A common redirection scenario for many web applications is to support automatic HTTP to HTTPS redirection to ensure all communication between application and its users occurs over an encrypted path. In the past, customers have used techniques such as creating a dedicated backend pool whose sole purpose is to redirect requests it receives on HTTP to HTTPS. With redirection support in Application Gateway, you can accomplish this simply by adding a new redirect configuration to a routing rule and specifying another listener with HTTPS protocol as the target listener.

The following types of redirection are supported:

  • 301 Permanent Redirect
  • 302 Found
  • 303 See Other
  • 307 Temporary Redirect

Application Gateway redirection support offers the following capabilities:

  • Global redirection: Redirects from one listener to another listener on the gateway. This enables HTTP to HTTPS redirection on a site.

  • Path-based redirection: Enables HTTP to HTTPS redirection only on a specific site area, for example a shopping cart area denoted by /cart/*.

  • Redirect to external site: Requires a new redirect configuration object, which specifies the target listener or external site to which redirection is desired. The configuration element also supports options to enable appending the URI path and query string to the redirected URL. The redirect configuration is attached to the source listener via a new rule.