Application Gateway listener configuration
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A listener is a logical entity that checks for incoming connection requests by using the port, protocol, host, and IP address. When you configure the listener, you must enter values for these 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.
When you create a new listener, you choose between basic and multi-site.
If you want all of your requests (for any domain) to be accepted and forwarded to backend pools, choose basic. Learn how to create an application gateway with a basic listener.
If you want to forward requests to different backend pools based on the host header or host names, choose multi-site listener. Application Gateway relies on HTTP 1.1 host headers to host more than one website on the same public IP address and port. To differentiate requests on the same port, you must specify a host name that matches with the incoming request. To learn more, see hosting multiple sites using Application Gateway.
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 will accept 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, unless rule priority is defined. If using rule priority, wildcard listeners should be defined a priority with a number greater than non-wildcard listeners, to ensure non-wildcard listeners execute prior to the wildcard listeners.
Frontend IP address
Choose the frontend IP address that you plan to associate with this listener. The listener will listen to incoming requests on this IP.
Application Gateway frontend supports dual-stack IP addresses (Public Preview). You can create up to four frontend IP addresses: Two IPv4 addresses (public and private) and two IPv6 addresses (public and private).
Associate a frontend port. You can 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. The same port can be used for public and private listeners.
When using private and public listeners with the same port number, your application gateway changes the "destination" of the inbound flow to the frontend IPs of your gateway. Hence, depending on your Network Security Group's configuration, you may need an inbound rule with Destination IP addresses as your application gateway's public and private frontend IPs.
- Source: (as per your requirement)
- Destination IP addresses: Public and Private frontend IPs of your application gateway.
- Destination Port: (as per listener configuration)
- Protocol: TCP
Outbound Rule: (no specific requirement)
Choose HTTP or HTTPS:
If you choose HTTP, the traffic between the client and the application gateway is unencrypted.
Choose HTTPS if you want TLS termination or end-to-end TLS encryption. The traffic between the client and the application gateway is encrypted and the TLS connection will be terminated at the application gateway. If you want end-to-end TLS encryption to the backend target, you must choose HTTPS within backend HTTP setting as well. This ensures that traffic is encrypted when application gateway initiates a connection to the backend target.
To configure TLS termination, a TLS/SSL certificate must be added to the listener. This allows the Application Gateway to decrypt incoming traffic and encrypt response traffic to the client. The certificate provided to the Application Gateway must be in Personal Information Exchange (PFX) format, which contains both the private and public keys.
When using a TLS certificate from Key Vault for a listener, you must ensure your Application Gateway always has access to that linked key vault resource and the certificate object within it. This enables seamless operations of TLS termination feature and maintains the overall health of your gateway resource. If an application gateway resource detects a misconfigured key vault, it automatically puts the associated HTTPS listener(s) in a disabled state. Learn more.
Additional protocol support
HTTP/2 protocol support is available to clients that connect to application gateway listeners only. Communication to backend server pools is always HTTP/1.1. By default, HTTP/2 support is disabled. The following Azure PowerShell code snippet shows how to enable this:
$gw = Get-AzApplicationGateway -Name test -ResourceGroupName hm
$gw.EnableHttp2 = $true
Set-AzApplicationGateway -ApplicationGateway $gw
You can also enable HTTP2 support using the Azure portal by selecting Enabled under HTTP2 in Application gateway > Configuration.
WebSocket support is enabled by default. There's no user-configurable setting to enable or disable it. You can use WebSockets with both HTTP and HTTPS listeners.
Custom error pages
You can define customized error pages for different response codes returned by the Application Gateway. The response codes for which you can configure error pages are 400, 403, 405, 408, 500, 502, 503, and 504. You can use global-level or listener-specific error page configuration to set them granularly for each listener. For more information, see Create Application Gateway custom error pages.
An error originating from the backend server is passed along unmodified by the Application Gateway to the client.
You can centralize TLS/SSL certificate management and reduce encryption-decryption overhead for a backend server farm. Centralized TLS handling also lets you specify a central TLS policy that's suited to your security requirements. You can choose predefined or custom TLS policy.
You configure TLS policy to control TLS protocol versions. You can configure an application gateway to use a minimum protocol version for TLS handshakes from TLS1.0, TLS1.1, TLS1.2, and TLS1.3. By default, SSL 2.0 and 3.0 are disabled and aren't configurable. For more information, see Application Gateway TLS policy overview.
After you create a listener, you associate it with a request-routing rule. That rule determines how requests that are received on the listener are routed to the back end.