I’ve recently been playing with the Application Gateway in Azure. Use case is pretty simple, serving as a simple load balancer / waf / dmz for an application that lives on some RHEL VM’s.
To Run App Gateway in its simplest configuration, you just have to;
– Create the vnet
– Create a subnet for the App Gateway (something like a /27 should do)
– Create a subnet for the VM’s
– Create the Application Gateway
– Create the VM’s (just with private ip’s)
– Add the VM’s to the backend pool
– Add an App Gateway NSG to allow port 80/443 and 65503-65534 for the health probe
– Add a VM subnet NSG to allow port 80 from the App Gateway subnet.
However, sometimes these things just don’t work and you need to fault find. The problem I had was that the gateway kept reporting a 502 error, and stating that all the nodes in the backend pool were unhealthy. This is a great article to start with, but didn’t help my problem.
What I then did was create another subnet and dropped a Windows VM jumpbox into it. From here, I could adequately browse the Linux VM’s in IE, as well as SSH onto them to check configuration from inside the same virtual network.
In the end, I created 6 different VM’s with different configuration before the problem became clear. Httpd was the problem.
|Windows Server 2016||IIS||Yes|
Because all the traffic on the private IP’s worked correctly from the jumpoff box, it’s clear that it wasn’t a firewall or nic configuration problem. The one consistent issue was httpd. After trying a few different settings changes in http.conf, I found the solution.
The default welcome page was causing the probe not to work. By creating an index.html file in /var/www/html/ the health probe began reporting success.