feat: [MSSQL] dont mask invalid iops combinations

[#185149472]

So far, other services preferred ignoring iops field when storage
type was not io1 or gp3. This implementation raises error instead.

The reasoning is to follow the principle of least surprise. If a
specific combination is invalid, enforce users to clearly specify
correct values.

There is some level of surprise though, because iops is 3000 by
default, so a customer might not be aware of this and still get
the error. However, even in that case, it might be useful to
surface the error to make the default value explicit and evident.

terraform-tests/mssql_test.go

@@ -330,43 +330,26 @@ var _ = Describe("mssql", Label("mssql-terraform"), Ordered, func() {
 			})
 		})
 
-		Context("storage_type gp2", func() {
-			BeforeAll(func() {
-				plan = ShowPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, map[string]any{
-					"storage_type": "gp2",
-				}))
-			})
-
-			It("iops should not be set", func() {
-				instanceData := AfterValuesForType(plan, "aws_db_instance")
-				Expect(instanceData).To(MatchKeys(IgnoreExtras, Keys{
-					"storage_type": Equal("gp2"),
-				}))
-				Expect("iops").NotTo(BeKeyOf(instanceData))
-			})
-		})
-
-		When("valid type for iops", func() {
-			DescribeTable("iops should be set",
-				func(storageTypeParam map[string]any) {
-					plan := ShowPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, storageTypeParam))
-					instanceData := AfterValuesForType(plan, "aws_db_instance")
-
-					Expect(instanceData).To(
-						MatchKeys(IgnoreExtras, Keys{
-							"storage_type": Equal(storageTypeParam["storage_type"]),
-						}),
-					)
-					Expect("iops").To(BeKeyOf(instanceData))
+		Context("storage_type and iops validation", func() {
+			DescribeTable("matrix with valid and invalid combinations",
+				func(extraParams map[string]any, expectedError string) {
+					if expectedError == "" {
+						ShowPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, extraParams))
+					} else {
+						session, _ := FailPlan(terraformProvisionDir, buildVars(defaultVars, requiredVars, extraParams))
+						Expect(session.ExitCode()).NotTo(Equal(0))
+						Expect(session).To(gbytes.Say(expectedError))
+
+					}
 				},
-				Entry(
-					"io1",
-					map[string]any{"storage_type": "io1"},
-				),
-				Entry(
-					"gp3",
-					map[string]any{"storage_type": "gp3"},
-				),
+				Entry("standard & iops", map[string]any{"storage_type": "standard", "iops": 3000}, "set `iops` to `null` or pick a valid `storage_type` such as io1, gp3"),
+				Entry("gp2      & iops", map[string]any{"storage_type": "gp2"     , "iops": 3000}, "set `iops` to `null` or pick a valid `storage_type` such as io1, gp3"),
+				Entry("gp3      & iops", map[string]any{"storage_type": "gp3"     , "iops": 3000}, ""),
+				Entry("io1      & iops", map[string]any{"storage_type": "io1"     , "iops": 3000}, ""),
+				Entry("standard ! iops", map[string]any{"storage_type": "standard", "iops": nil}, ""),
+				Entry("gp2      ! iops", map[string]any{"storage_type": "gp2"     , "iops": nil}, ""),
+				Entry("gp3      ! iops", map[string]any{"storage_type": "gp3"     , "iops": nil}, "specify an `iops` value or pick a `storage_type` different than io1, gp3"),
+				Entry("io1      ! iops", map[string]any{"storage_type": "io1"     , "iops": nil}, "specify an `iops` value or pick a `storage_type` different than io1, gp3"),
 			)
 		})
 	})

terraform/mssql/provision/data.tf

@@ -5,8 +5,6 @@ locals {
   subnet_ids         = try(data.aws_db_subnet_group.provided[0].subnet_ids, data.aws_subnets.in_provided_vpc[0].ids, data.aws_subnets.in_default_vpc[0].ids)
   security_group_ids = try(data.aws_security_groups.provided[0].ids, [aws_security_group.rds-sg[0].id])
   subnet_group_name  = try(data.aws_db_subnet_group.provided[0].name, aws_db_subnet_group.rds-private-subnet[0].name)
-
-  valid_storage_types_for_iops = ["io1", "gp3"]
 }
 
 data "aws_vpc" "default" {

terraform/mssql/provision/main.tf

@@ -51,7 +51,7 @@ resource "aws_db_instance" "db_instance" {
   kms_key_id             = var.kms_key_id == "" ? null : var.kms_key_id
   skip_final_snapshot    = true
   storage_type           = var.storage_type
-  iops                   = contains(local.valid_storage_types_for_iops, var.storage_type) ? var.iops : null
+  iops                   = var.iops
 
   lifecycle {
     prevent_destroy = true

terraform/mssql/provision/validations.tf

@@ -8,3 +8,26 @@ resource "terraform_data" "kms_key_was_provided" {
     }
   }
 }
+
+resource "terraform_data" "iops-based-storage-type" {
+  count = var.iops != null ? 1 : 0
+
+  lifecycle {
+    precondition {
+      condition     = contains(["io1", "gp3"], var.storage_type)
+      error_message = "set `iops` to `null` or pick a valid `storage_type` such as io1, gp3"
+    }
+  }
+}
+
+resource "terraform_data" "non-iops-based-storage-type" {
+  count = var.iops == null ? 1 : 0
+
+  lifecycle {
+    precondition {
+      condition     = !contains(["io1", "gp3"], var.storage_type)
+      error_message = "specify an `iops` value or pick a `storage_type` different than io1, gp3"
+    }
+  }
+}
+