What Is The Cheapest VM That Can Be Used As An AKS Node?

You need to select an instance with at least 3.5 GB of memory. Read A note on node size from this blog. You can list the VM size and price on the Azure sales site.

Currently, the cheapest is Standard_B2s with 4 GB RAM. You can also sort it directly in the Azure portal.

You do a B1 which is cheaper than B2 if you resize the vmss, then upgrade the instance.This one is $3.80/month for Linux and $10.22/month for Windows

For whatever reason you can't do this in Terraform yet.

Step 1:Click on vmss -> settings -> size -> see all sizes (in small print) -> resize

Step 2:Click on vmss -> settings -> instance -> _0 -> upgrade (at top controller bar)

I wouldn't worry about the vm instance size too much. This is where Terraform rips you off. os_disk_size_gb. Set this lower otherwise it defaults to $20/month per instance. There seems to be no way to change the tier, they defaulted to a premium 128GB disk, and made it seem like you would only spend $30 per node.

UPDATE:I started experiencing some problems with instance at size b1ls.

Just to add to existing answer. I dont think there is an enum to list all the valid sizes of vms, but if you look at the API definition, it lists all of them pretty clearly.

And you can use azureprice.net or something similar to figure out cheapest vm for your region (usually its B series).