feat: Support no read-replication for Memorystore

Refs: #DEVOP-4801

Signed-off-by: Christian Witts <christian@honestbank.com>

modules/memstore_redis/README.md

@@ -9,7 +9,7 @@
 
 | Name | Version |
 |------|---------|
-| <a name="provider_google"></a> [google](#provider\_google) | 4.29.0 |
+| <a name="provider_google"></a> [google](#provider\_google) | 5.38.0 |
 
 ## Modules
 
@@ -33,7 +33,7 @@ No modules.
 | <a name="input_read_replicas_enabled"></a> [read\_replicas\_enabled](#input\_read\_replicas\_enabled) | Whether to enable read replicas | `bool` | `false` | no |
 | <a name="input_redis_version"></a> [redis\_version](#input\_redis\_version) | The version of Redis to use | `string` | n/a | yes |
 | <a name="input_region"></a> [region](#input\_region) | The region to create the instance in | `string` | `"asia-southeast2"` | no |
-| <a name="input_replicas"></a> [replicas](#input\_replicas) | The number of instances to create | `number` | `1` | no |
+| <a name="input_replicas"></a> [replicas](#input\_replicas) | The number of read replicas to create | `number` | `0` | no |
 | <a name="input_reserved_ip_range"></a> [reserved\_ip\_range](#input\_reserved\_ip\_range) | The reserved IP range to use for the instance | `string` | `null` | no |
 | <a name="input_tier"></a> [tier](#input\_tier) | The tier of the instance | `string` | n/a | yes |
 | <a name="input_zone"></a> [zone](#input\_zone) | The location to create the instance in | `string` | n/a | yes |

modules/memstore_redis/main.tf

@@ -11,13 +11,13 @@ terraform {
 resource "google_redis_instance" "cache" {
   name           = replace(var.name, " ", "-")
   tier           = var.tier
-  memory_size_gb = var.memory_size
+  memory_size_gb = local.memory_size
   auth_enabled   = true
 
   location_id             = "${var.region}-${var.zone}"
   alternative_location_id = var.tier == "STANDARD_HA" ? "${var.region}-${var.alternative_zone}" : ""
 
-  replica_count      = var.tier == "STANDARD_HA" ? var.replicas : 0
+  replica_count      = local.replica_count
   read_replicas_mode = var.read_replicas_enabled ? "READ_REPLICAS_ENABLED" : "READ_REPLICAS_DISABLED"
 
   authorized_network = var.network_id

modules/memstore_redis/validations.tf

@@ -0,0 +1,8 @@
+locals {
+  # Generate invalid values to be used so that the module fails based on composite
+  # scenarios as validation conditions only apply to the variable scoped for the
+  # validation condition.
+  memory_size   = var.read_replicas_enabled && var.memory_size >= 5 ? var.memory_size : 0
+  replicas      = var.tier == "STANDARD_HA" ? var.replicas : 0
+  replica_count = var.read_replicas_enabled && local.replicas > 0 ? var.replicas : 0
+}

modules/memstore_redis/variables.tf

@@ -40,7 +40,6 @@ variable "reserved_ip_range" {
   description = "The reserved IP range to use for the instance"
 }
 
-
 variable "memory_size" {
   type        = string
   default     = "2"
@@ -49,11 +48,11 @@ variable "memory_size" {
 
 variable "replicas" {
   type        = number
-  default     = 1
-  description = "The number of instances to create"
+  default     = 0
+  description = "The number of read replicas to create"
   validation {
-    condition     = var.replicas >= 1 && var.replicas <= 5
-    error_message = "The valid range for the Standard Tier with read replicas enabled is [1-5] and defaults to 1."
+    condition     = var.replicas <= 5
+    error_message = "The valid range for the Standard Tier with read replicas enabled is [1-5] and defaults to 0 as the default is zero read-replicas."
   }
 }