Add experimental validation

variables.tf

@@ -1,6 +1,13 @@
 variable "project_slug" {
   type = string
   description = "A slugified name, used to label AWS resources."
+  validation {
+    // Ensures that the slug does not start or end with a period or dash
+    // Ensures that the overall slug is no longer than 52 characters, which allows this to be used
+    // for the assetstore bucket name (the overall bucket name must be less than 63 characters)
+    condition     = can(regex("^[a-z0-9]+[a-z0-9.-]{0,50}[a-z0-9]+$", var.project_slug))
+    error_message = "The project_slug value may contain only lowercase letters, numbers, periods, and dashes."
+  }
 }
 
 variable "ec2_instance_type" {
@@ -12,6 +19,10 @@ variable "ec2_ami" {
   type = string
   default = "ami-0ac80df6eff0e70b5"
   description = "The base AMI ID for the server."
+  validation {
+    condition     = can(regex("^ami-", var.ec2_ami))
+    error_message = "The ec2_ami value must be a valid AMI id, starting with \"ami-\"."
+  }
 }
 variable "ssh_public_key" {
   type = string