Merge pull request #288374 from reyjordi/tcp-keep-alive-edit

added info about tcp idle timeout and keep alive timeout

Author: JamesJBarnett

articles/application-gateway/application-gateway-faq.yml

@@ -67,7 +67,7 @@ sections:
         answer: |
           `Keep-Alive` timeout governs how long the application gateway waits for a client to send another HTTP request on a persistent connection before reusing it or closing it. TCP idle timeout governs how long a TCP connection is kept open if there's no activity. 
           
-          The `Keep-Alive` timeout in the Application Gateway v1 SKU is 120 seconds and in the v2 SKU it's 75 seconds. For private IP addresses, the value is nonconfigurable with a TCP idle timeout of 5 minutes. The TCP idle timeout is a 4-minute default on the frontend virtual IP (VIP) of both v1 and v2 SKU of Application Gateway. You can configure the TCP idle timeout value on v1 and v2 Application Gateway instances to be anywhere between 4 minutes and 30 minutes. For both v1 and v2 Application Gateway instances, you need to go to the public IP of the application gateway and change the TCP idle timeout under the **Configuration** pane of the public IP in the portal. You can set the TCP idle timeout value of the public IP through PowerShell by running the following commands: 
+          For HTTP/1.1 connections, the `Keep-Alive` timeout in the Application Gateway v1 and v2 SKU is 120 seconds. For private IP addresses, the value is nonconfigurable with a TCP idle timeout of 5 minutes. The TCP idle timeout is a 4-minute default on the frontend virtual IP (VIP) of both v1 and v2 SKU of Application Gateway. You can configure the TCP idle timeout value on v1 and v2 Application Gateway instances to be anywhere between 4 minutes and 30 minutes. For both v1 and v2 Application Gateway instances, you need to go to the public IP of the application gateway and change the TCP idle timeout under the **Configuration** pane of the public IP in the portal. You can set the TCP idle timeout value of the public IP through PowerShell by running the following commands: 
           
           ```azurepowershell-interactive
           $publicIP = Get-AzPublicIpAddress -Name MyPublicIP -ResourceGroupName MyResourceGroup
@@ -77,6 +77,8 @@ sections:
 
           For HTTP/2 connections to the frontend IP address on Application Gateway v2 SKU, the idle timeout is set to 180 seconds and is nonconfigurable.
           
+          To prevent conflict and unexpected behavior, make sure that the TCP idle timeout is set to be the same as or longer than the keep-alive timeout.
+          
       - question: Does Application Gateway reuse the TCP connection that's established with a backend server?
         answer: Yes. Application Gateway reuses the existing TCP connections with a backend server.