404 error in url based routing using Application Gateway

Question

I have 2 web apps behind Application Gateway. I am trying to access by http://<aap_gateway_pub_ip>/web1 should go to http://webapp1.azurewebsites.net and http://<aap_gateway_pub_ip>/web2 should go to http://webapp2.azurewebsites.net. I have defined path based rule like:

$web1PathRule = New-AzureRmApplicationGatewayPathRuleConfig -Name web1pathrule -Paths "/web1" -BackendAddressPool $regbackendpool -BackendHttpSettings $poolSetting

$web2PathRule = New-AzureRmApplicationGatewayPathRuleConfig -Name web2pathrule  -Paths "/web2" -BackendAddressPool $accbackendpool -BackendHttpSettings $poolSetting

$urlpathmap = New-AzureRmApplicationGatewayUrlPathMapConfig -Name urlpathmap -PathRules $web1PathRule, $web2PathRule -DefaultBackendAddressPool $defaultPool -DefaultBackendHttpSettings $poolSetting

$urlRoutingRule = New-AzureRmApplicationGatewayRequestRoutingRule -Name routingrule-001 -RuleType PathBasedRouting -HttpListener $defaultlistener -UrlPathMap $urlpathmap

The issue is when I directly access http://<aap_gateway_pub_ip> request goes to default pool which is web1 backendpool and opens web1 app. But when I access http://<aap_gateway_pub_ip>/web1, it returns 404 error.

What additional configuration is required to make this working?

Answer 1

I also got stuck in this problem for a day and trust me Microsoft should think about and adding more clear instructions.

The thing is when you access the base address of frontend IP like this http://<aap_gateway_pub_ip> It simply replace the frontend IP with the backend pool based web app IP, so the request sent to the web app is something like http://webapp1.azurewebsites.net and it works.

Problem starts when you create a path based rule and configure it like this http://<aap_gateway_pub_ip>/web1 -> http://webapp1.azurewebsites.net

What app gateway does, it simply replace the front end ip with the backend ip
So the request sent to backend is

http://webapp1.azurewebsites.net/web1

and if your backend webapp does not contain that page in the website then it will through 404 error.

So there are 2 solutions for that

1> Edit the httpsetting of the rule and add a '/' in the "override backend path"

2> The other approach is to actually drive the path based rule in such a way that the final path (like web1 in your case) should actually exists in the backend server or webapp.

Answer 2

Please follow additional backend http settings and probe configuration for integration with Web Apps to work correctly. The documentation is here.