How to setup azure application gateway with App services - azure

Question

I am trying to setup azure application gateway with self signed cert. for the first step without https, I am trying to establish the http with port 80. when I try to browse the application with the appgateway public IP it is redirecting it to https://myappname.azurewebsites.net:80, I am not sure whats going wrong here. I specifically write a rewrite rule to override to the the site but in that case the site loads without redirection(as expected) and working fine. I want to understand why its navigating to myappname.azurewebsites.net:80 instead of just myappname.azurewebsites.net. I am following this
Here is the simplified version of the PowerShell script for the same with no existing port 80 rule
$webAppFQDN = "myapp.azurewebsites.net"
$rgName = "acsrg001"
$appGwName = "acsag002"
$appGwBackendPoolNameForAppSvc = "acspebpool001"
$httpSettingsName = "acspehttpsettings001"
$httpListenerName = "acspelistener001"
$reqRoutingRuleName = "acspelatestrule001"
$gw = Get-AzApplicationGateway -Name $appGwName -ResourceGroupName $rgName
Add-AzApplicationGatewayBackendAddressPool -Name $appGwBackendPoolNameForAppSvc -ApplicationGateway $gw -BackendFqdns $webAppFQDN
Set-AzApplicationGateway -ApplicationGateway $gw
$gw = Get-AzApplicationGateway -Name $appGwName -ResourceGroupName $rgName
Add-AzApplicationGatewayBackendHttpSettings -Name $httpSettingsName -ApplicationGateway $gw -Protocol Https -Port 443 -PickHostNameFromBackendAddress -CookieBasedAffinity Disabled -RequestTimeout 30
Set-AzApplicationGateway -ApplicationGateway $gw
$gw = Get-AzApplicationGateway -Name $appGwName -ResourceGroupName $rgName
$port = $gw.FrontendPorts | Where-Object {$_.Port -eq 80}
$listener = $gw.HttpListeners | Where-Object {$_.Protocol.ToString().ToLower() -eq "http" -and $_.FrontendPort.Id -eq $port.Id}
if ($listener -eq $null){
$frontendIpConfig = $gw.FrontendIpConfigurations | Where-Object {$_.PublicIpAddress -ne $null}
Add-AzApplicationGatewayHttpListener -Name $httpListenerName -ApplicationGateway $gw -Protocol Http -FrontendIPConfiguration $frontendIpConfig -FrontendPort $port
Set-AzApplicationGateway -ApplicationGateway $gw
}
$gw = Get-AzApplicationGateway -Name $appGwName -ResourceGroupName $rgName
$httpListener = Get-AzApplicationGatewayHttpListener -Name $httpListenerName -ApplicationGateway $gw
$httpSettings = Get-AzApplicationGatewayBackendHttpSettings -Name $httpSettingsName -ApplicationGateway $gw
$backendPool = Get-AzApplicationGatewayBackendAddressPool -Name $appGwBackendPoolNameForAppSvc -ApplicationGateway $gw
Add-AzApplicationGatewayRequestRoutingRule -Name $reqRoutingRuleName -ApplicationGateway $gw -RuleType Basic -BackendHttpSettings $httpSettings -HttpListener $httpListener -BackendAddressPool $backendPool -Priority 1
Set-AzApplicationGateway -ApplicationGateway $gw
$gw = Get-AzApplicationGateway -Name $appGwName -ResourceGroupName $rgName
Get-AzApplicationGatewayBackendHealth -ResourceGroupName $rgName -Name $appGwName

Answer 1

I tried to reproduce the same script in my environment I got the same result like below:
Sku : Microsoft.Azure.Commands.Network.Models.PSApplicationGatewaySku
SslPolicy :
GatewayIPConfigurations : {appGatewayIpConfig}
AuthenticationCertificates : {}
SslCertificates : {}
TrustedRootCertificates : {}
TrustedClientCertificates : {}
FrontendIPConfigurations : {appGwPublicFrontendIp}
FrontendPorts : {port_80}
Probes : {}
BackendAddressPools : {back, pool1, backendpool007}
BackendHttpSettingsCollection : {http}
SslProfiles : {}
HttpListeners : {listhttp}
UrlPathMaps : {}
RequestRoutingRules : {rule1}
RewriteRuleSets : {}
RedirectConfigurations : {rule1}
WebApplicationFirewallConfiguration :
FirewallPolicy :
AutoscaleConfiguration : Microsoft.Azure.Commands.Network.Models.PSApplicationGatewayAutoscaleConfiguration
CustomErrorConfigurations : {}
PrivateLinkConfigurations : {}
PrivateEndpointConnections : {}
EnableHttp2 : False
EnableFips :
ForceFirewallPolicyAssociation :
Zones : {}
OperationalState : Running
ProvisioningState : Succeeded
Identity :
GatewayIpConfigurationsText : [
{
"Subnet": {
"Id": "/subscriptions/6ca9eff3-3c2d-420e-875e-ea526b412ca0/resourceGroups/imran/providers/Microsoft.Network/virtualNetworks/imran-vnet/su
bnets/appsubnet"
},
"ProvisioningState": "Succeeded",
"Type": "Microsoft.Network/applicationGateways/gatewayIPConfigurations",
"Name": "appGatewayIpConfig",
"Etag": "W/\"2494e0c1-b1fc-4840-896e-a39e9ebf0846\"",
"Id": "/subscriptions/6ca9eff3-3c2d-420e-875e-ea526b412ca0/resourceGroups/imran/providers/Microsoft.Network/applicationGateways/imran/gatew
ayIPConfigurations/appGatewayIpConfig"
}
This issue may cause having a different hostname at the reverse proxy in app gateway one of the back-end application servers can cause cookies or redirect URLs to malfunction. For instance, the session state may be lost, authentication may fail, or back-end URLs may unintentionally discover back-end URLs.
To resolve this issue, Try to add a custom domain Configure App Service with Application Gateway along with a certificate in your backend pool with use of custom domain and add authentication trusted root certificates of back-end servers like below:
In application gateway under setting click rules in backend target -> add backend pool of app service and Add appropriate App Gateway in the HTTP configuration.
You can check the similar thread for reference:
when I hit application gateway's public ip, I get redirected to app service dns. by GitaraniSharma
Azure application gateway with Web App - Gateway IP wont work