Adds default PostgreSQL server configuration

Signed-off-by: PhanikumarThodupunoori <[email protected]>

Author: PhanikumarThodupunoori

docs/CONFIG-VARS.md

@@ -278,6 +278,18 @@ Each server element, like `foo = {}`, can contain none, some, or all of the para
   - `edition` must be `"ENTERPRISE"`
   - `machine_type` must start with `"db-custom-"`
 
+*NOTE*: The default = {} elements is always required when creating external databases. This is the systems default database server.
+
+If you provide an empty block for default, the following default values will be used:
+terraform
+postgres_servers = {
+  default = {
+    server_version = "15"
+    edition        = "ENTERPRISE"
+    machine_type   = "db-custom-4-16384"
+  }
+}
+
 | Name | Description | Type | Default | Notes |
 | :--- | ---: | ---: | ---: | ---: |
 | machine_type| The machine type for the PostgreSQL server VMs" | string | "db-custom-4-16384" | Google Cloud Postgres supports only shared-core machine types such as db-f1-micro, and custom machine types such as db-custom-2-13312. Must match the PostgreSQL version requirements. |

variables.tf

@@ -390,7 +390,13 @@ variable "postgres_server_defaults" {
 variable "postgres_servers" {
   description = "Map of PostgreSQL server objects"
   type        = any
-  default     = null
+  default     = {
+    default = {
+      server_version = "15"
+      edition        = "ENTERPRISE"
+      machine_type   = "db-custom-4-16384"
+    }
+  }
 
   # Checking for user provided "default" server
   validation {
@@ -414,9 +420,14 @@ variable "postgres_servers" {
   validation {
     condition = var.postgres_servers != null ? length(var.postgres_servers) != 0 ? alltrue([
       for k, v in var.postgres_servers : (
-        v.server_version != null && (
-          (tonumber(v.server_version) >= 16 && v.edition == "ENTERPRISE_PLUS" && can(regex("^db-perf-optimized-N-", v.machine_type))) ||
-          (tonumber(v.server_version) < 16 && v.edition == "ENTERPRISE" && can(regex("^db-custom-", v.machine_type)))
+        # If the object is empty, use default values
+        length(keys(v)) == 0 ? true : (
+          can(try(v.server_version, null)) && 
+          can(try(v.edition, null)) && 
+          can(try(v.machine_type, null)) && (
+            (tonumber(try(v.server_version, "15")) >= 16 && try(v.edition, "ENTERPRISE") == "ENTERPRISE_PLUS" && can(regex("^db-perf-optimized-N-", try(v.machine_type, "")))) ||
+            (tonumber(try(v.server_version, "15")) < 16 && try(v.edition, "ENTERPRISE") == "ENTERPRISE" && can(regex("^db-custom-", try(v.machine_type, ""))))
+          )
         )
       )
     ]) : false : true