Create a private DNS zone

The app on vm-app connects to its database, vm-db, by its IP 10.1.3.4, and that IP is about to change. Give vm-db a name instead. DNS is what turns a name into an IP. Create the private DNS zone lab.internal, add a record db pointing at 10.1.3.4, so db.lab.internal means vm-db, link the zone to vnet-app, and check the name from vm-app.

1. Create the zone.

   az network private-dns zone create -g rg-lab --name lab.internalType it
   What's this?

   Works with a private DNS zone: the names it holds, or which virtual networks can use it.

   • -g the resource group the resources live in
   • --name the name of the thing to look at or change

2. Add the db record.

   az network private-dns record-set a add-record -g rg-lab --zone-name lab.internal --record-set-name db --ipv4-address 10.1.3.4Type it
   What's this?

   Adds or changes an A record: a name in the zone that points to an IP address.

   • -g the resource group the resources live in
   • --zone-name the private DNS zone
   • --record-set-name db the name inside the zone, so db.lab.internal
   • --ipv4-address the address it answers with

3. Link the zone to vnet-app, without auto-registration.

   az network private-dns link vnet create -g rg-lab --zone-name lab.internal --name link-app --virtual-network vnet-app --registration-enabled falseType it
   What's this?

   Creates a virtual network with its address space.

   • -g the resource group the resources live in
   • --zone-name the private DNS zone
   • --name the name of the thing to look at or change

4. Connect to vm-app.

   ssh vm-appType it
   What's this?

   Opens a shell on vm-app, so the next commands run on that VM. In this lab it's a shortcut. In real Azure you'd connect through something like Azure Bastion, or SSH to an address you can reach.

5. Look the name up. nslookup asks DNS for a name's IP. It should answer 10.1.3.4. Type exit when done.

   nslookup db.lab.internalType it
   What's this?

   Asks the VM's DNS server what IP address a name points to. Run it on the VM that has the problem, because each VM can get a different answer.