Skip builder vhd upload if no builders created

Signed-off-by: Henri Rosten <[email protected]>

terraform/README.md

@@ -192,7 +192,7 @@ Example fix:
 │ If you wish to store the current configuration with no changes to the state, use "terraform init -reconfigure".
 ```
 
-Above error (or similar) is likely caused by changed terraform backend state.
+Above error (or similar) is caused by changed terraform backend state.
 Fix the local state reference by removing local state files and re-running `terraform-init.sh`:
 
 ```bash
@@ -202,3 +202,22 @@ Fix the local state reference by removing local state files and re-running `terr
 # Replace 'workspacename' with the name of the workspace you'll work with
 ❯ ./terraform-init.sh -w workspacename
 ```
+
+#### Error: creating/updating Image
+```bash
+❯ terraform apply -auto-approve
+...
+│ Error: creating/updating Image (Subscription: "<SUBID>"
+│ Resource Group Name: "ghaf-infra-henri"
+│ Image Name: "binary-cache"): performing CreateOrUpdate: unexpected status 400 (400 Bad Request) with error: InvalidParameter: The source blob https://imghenrieun.blob.core.windows.net/ghaf-infra-vm-images/binary-cache.vhd is not accessible.
+│
+│   with module.binary_cache_image.azurerm_image.default,
+│   on modules/azurerm-nix-vm-image/main.tf line 32, in resource "azurerm_image" "default":
+│   32: resource "azurerm_image" "default" {
+```
+
+Above error (or similar) is likely caused by a bug in terraform azurerm provider: it appears it tries to use the uploaded vhd image too soon after upload, while it's still not fully available. It frequently occurs on deploying a clean (previously undeployed) ghaf-infra environment. Fix the issue by running terraform apply again:
+
+```bash
+❯ terraform apply -auto-approve
+```

terraform/builder.tf

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 module "builder_image" {
+  count  = local.num_builders
   source = "./modules/azurerm-nix-vm-image"
 
   nix_attrpath   = ""
@@ -32,7 +33,7 @@ module "builder_vm" {
   virtual_machine_name         = "ghaf-builder-x86-${count.index}-${local.ws}"
   virtual_machine_size         = local.opts[local.conf].vm_size_builder_x86
   virtual_machine_osdisk_size  = local.opts[local.conf].osdisk_size_builder
-  virtual_machine_source_image = module.builder_image.image_id
+  virtual_machine_source_image = module.builder_image[count.index].image_id
 
   virtual_machine_custom_data = join("\n", ["#cloud-config", yamlencode({
     users = [{