Adding existing Azure VMs (classic) to a virtual network
On Azure, I have a two-VM set (both classic), whereby my web application resides on one VM, my database on another. Both map to the same DNS and belong to the same Resource Group, but both are acting as standalone cloud services at the moment. Let me explain: currently the web application communicates with the database over the public DNS. However, I need them to be on the same lan, so I can de-risk security and improve latency.
I know for a fact that they're not part of a virtual network because when I try to affix a static private IP to my database VM, I'm shown the following prompt in the portal:
This virtual machine can't be configured with a static private IP address because it's not deployed in a virtual network.
How should I proceed to fix this misconfiguration and what should my next concrete step be? The website is live, and I don't want to risk service interruption. Ideally, both VMs should be in the same virtual network, and should communicate with eachother via a static internal IP. Please forgive my ignorance. Any help would be greatly appreciated.
I guess i'll be the bearer of bad news. You have to delete both VMs while keeping the VHDs in the storage account, then recreate the VMs (reattaching the disks) in the Virtual Network.
Since these are Classic VMs you can use the old Portal when re-creating them. You'll find the VHDs under "My Disks" in the VM creation workflow.
Alternatively, just restrict the inbound access with an ACL on the database Endpoint. Allow the VIP of the first VM and deny everything else. This is good enough for almost any scenario, since if your Web Server gets compromised it's game over. It makes no difference how they exfiltrate stuff off your database (over a VNET or over VIP).
Here's the relevant documentation page for setting up Endpoint ACLs: