fix: improve doc for Spanner instance_config input and update env_vars output (GoogleCloudPlatform#75)

Author: q2w

README.md

@@ -62,7 +62,7 @@ Functional examples are included in the
 | enable\_autoscaling | Enable autoscaling for the Spanner Instance | `bool` | `false` | no |
 | force\_destroy | Whether to force destroy the instance and its backups. | `bool` | `false` | no |
 | high\_priority\_cpu\_utilization\_percent | Target high priority CPU utilization percentage for autoscaling. | `number` | `60` | no |
-| instance\_config | The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance. | `string` | n/a | yes |
+| instance\_config | The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance. It determines where your data is stored. Values are typically of the form regional-europe-west1, us-central etc. In order to obtain a valid list please consult the https://cloud.google.com/spanner/docs/instance-configurations | `string` | n/a | yes |
 | instance\_display\_name | The descriptive name for this instance as it appears in UIs. | `string` | `"spanner-instance"` | no |
 | instance\_iam | The list of permissions on spanner instance | `list(string)` | `[]` | no |
 | instance\_labels | A set of key/value label pairs to assign to the spanner instance | `map(string)` | `{}` | no |

metadata.yaml

@@ -56,7 +56,7 @@ spec:
         varType: string
         defaultValue: spanner-instance
       - name: instance_config
-        description: The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance.
+        description: The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance. It determines where your data is stored. Values are typically of the form regional-europe-west1, us-central etc. In order to obtain a valid list please consult the https://cloud.google.com/spanner/docs/instance-configurations
         varType: string
         required: true
       - name: instance_size

outputs.tf

@@ -39,7 +39,7 @@ output "env_vars" {
   description = "Map of environment variables for Spanner databases with keys as project_id:instance_name:database_name and values as fully qualified database paths"
   value = {
     for k, v in local.database_creation_list :
-    "${var.project_id}:${var.instance_name}:${k}" => "projects/${var.project_id}/instances/${var.instance_name}/databases/${k}"
+    replace("${var.project_id}_${var.instance_name}_${k}", "-", "_") => "projects/${var.project_id}/instances/${var.instance_name}/databases/${k}"
   }
 }
 

variables.tf

@@ -31,7 +31,7 @@ variable "instance_display_name" {
 }
 
 variable "instance_config" {
-  description = "The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance."
+  description = "The name of the instance's configuration (similar but not quite the same as a region) which defines the geographic placement and replication of your databases in this instance. It determines where your data is stored. Values are typically of the form regional-europe-west1, us-central etc. In order to obtain a valid list please consult the https://cloud.google.com/spanner/docs/instance-configurations"
   type        = string
 }