diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..24e2673
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.terraform
+.cache
\ No newline at end of file
diff --git a/alarms.tf b/alarms.tf
index dccf270..d9c5b76 100644
--- a/alarms.tf
+++ b/alarms.tf
@@ -1,5 +1,5 @@
 resource "aws_cloudwatch_metric_alarm" "alarm_rds_DatabaseConnections_writer" {
-  count               = "${var.cw_alarms ? 1 : 0}"
+  count               = var.cw_alarms ? 1 : 0
   alarm_name          = "${aws_rds_cluster.default.id}-alarm-rds-writer-DatabaseConnections"
   comparison_operator = "GreaterThanOrEqualToThreshold"
   evaluation_periods  = "1"
@@ -7,19 +7,19 @@ resource "aws_cloudwatch_metric_alarm" "alarm_rds_DatabaseConnections_writer" {
   namespace           = "AWS/RDS"
   period              = "60"
   statistic           = "Sum"
-  threshold           = "${var.cw_max_conns}"
+  threshold           = var.cw_max_conns
   alarm_description   = "RDS Maximum connection Alarm for ${aws_rds_cluster.default.id} writer"
-  alarm_actions       = ["${var.cw_sns_topic}"]
-  ok_actions          = ["${var.cw_sns_topic}"]
+  alarm_actions       = [var.cw_sns_topic]
+  ok_actions          = [var.cw_sns_topic]
 
-  dimensions {
-    DBClusterIdentifier = "${aws_rds_cluster.default.id}"
+  dimensions = {
+    DBClusterIdentifier = aws_rds_cluster.default.id
     Role                = "WRITER"
   }
 }
 
 resource "aws_cloudwatch_metric_alarm" "alarm_rds_DatabaseConnections_reader" {
-  count               = "${var.cw_alarms && var.replica_count > 0 ? 1 : 0}"
+  count               = var.cw_alarms && var.replica_count > 0 ? 1 : 0
   alarm_name          = "${aws_rds_cluster.default.id}-alarm-rds-reader-DatabaseConnections"
   comparison_operator = "GreaterThanOrEqualToThreshold"
   evaluation_periods  = "1"
@@ -27,19 +27,19 @@ resource "aws_cloudwatch_metric_alarm" "alarm_rds_DatabaseConnections_reader" {
   namespace           = "AWS/RDS"
   period              = "60"
   statistic           = "Maximum"
-  threshold           = "${var.cw_max_conns}"
+  threshold           = var.cw_max_conns
   alarm_description   = "RDS Maximum connection Alarm for ${aws_rds_cluster.default.id} reader(s)"
-  alarm_actions       = ["${var.cw_sns_topic}"]
-  ok_actions          = ["${var.cw_sns_topic}"]
+  alarm_actions       = [var.cw_sns_topic]
+  ok_actions          = [var.cw_sns_topic]
 
-  dimensions {
-    DBClusterIdentifier = "${aws_rds_cluster.default.id}"
+  dimensions = {
+    DBClusterIdentifier = aws_rds_cluster.default.id
     Role                = "READER"
   }
 }
 
 resource "aws_cloudwatch_metric_alarm" "alarm_rds_CPU_writer" {
-  count               = "${var.cw_alarms ? 1 : 0}"
+  count               = var.cw_alarms ? 1 : 0
   alarm_name          = "${aws_rds_cluster.default.id}-alarm-rds-writer-CPU"
   comparison_operator = "GreaterThanOrEqualToThreshold"
   evaluation_periods  = "2"
@@ -47,19 +47,19 @@ resource "aws_cloudwatch_metric_alarm" "alarm_rds_CPU_writer" {
   namespace           = "AWS/RDS"
   period              = "60"
   statistic           = "Maximum"
-  threshold           = "${var.cw_max_cpu}"
+  threshold           = var.cw_max_cpu
   alarm_description   = "RDS CPU Alarm for ${aws_rds_cluster.default.id} writer"
-  alarm_actions       = ["${var.cw_sns_topic}"]
-  ok_actions          = ["${var.cw_sns_topic}"]
+  alarm_actions       = [var.cw_sns_topic]
+  ok_actions          = [var.cw_sns_topic]
 
-  dimensions {
-    DBClusterIdentifier = "${aws_rds_cluster.default.id}"
+  dimensions = {
+    DBClusterIdentifier = aws_rds_cluster.default.id
     Role                = "WRITER"
   }
 }
 
 resource "aws_cloudwatch_metric_alarm" "alarm_rds_CPU_reader" {
-  count               = "${var.cw_alarms && var.replica_count > 0 ? 1 : 0}"
+  count               = var.cw_alarms && var.replica_count > 0 ? 1 : 0
   alarm_name          = "${aws_rds_cluster.default.id}-alarm-rds-reader-CPU"
   comparison_operator = "GreaterThanOrEqualToThreshold"
   evaluation_periods  = "2"
@@ -67,19 +67,19 @@ resource "aws_cloudwatch_metric_alarm" "alarm_rds_CPU_reader" {
   namespace           = "AWS/RDS"
   period              = "60"
   statistic           = "Maximum"
-  threshold           = "${var.cw_max_cpu}"
+  threshold           = var.cw_max_cpu
   alarm_description   = "RDS CPU Alarm for ${aws_rds_cluster.default.id} reader(s)"
-  alarm_actions       = ["${var.cw_sns_topic}"]
-  ok_actions          = ["${var.cw_sns_topic}"]
+  alarm_actions       = [var.cw_sns_topic]
+  ok_actions          = [var.cw_sns_topic]
 
-  dimensions {
-    DBClusterIdentifier = "${aws_rds_cluster.default.id}"
+  dimensions = {
+    DBClusterIdentifier = aws_rds_cluster.default.id
     Role                = "READER"
   }
 }
 
 resource "aws_cloudwatch_metric_alarm" "alarm_rds_replica_lag" {
-  count               = "${var.cw_alarms && var.replica_count > 0 ? 1 : 0}"
+  count               = var.cw_alarms && var.replica_count > 0 ? 1 : 0
   alarm_name          = "${aws_rds_cluster.default.id}-alarm-rds-reader-AuroraReplicaLag"
   comparison_operator = "GreaterThanOrEqualToThreshold"
   evaluation_periods  = "5"
@@ -87,13 +87,14 @@ resource "aws_cloudwatch_metric_alarm" "alarm_rds_replica_lag" {
   namespace           = "AWS/RDS"
   period              = "60"
   statistic           = "Maximum"
-  threshold           = "${var.cw_max_replica_lag}"
+  threshold           = var.cw_max_replica_lag
   alarm_description   = "RDS CPU Alarm for ${aws_rds_cluster.default.id}"
-  alarm_actions       = ["${var.cw_sns_topic}"]
-  ok_actions          = ["${var.cw_sns_topic}"]
+  alarm_actions       = [var.cw_sns_topic]
+  ok_actions          = [var.cw_sns_topic]
 
-  dimensions {
-    DBClusterIdentifier = "${aws_rds_cluster.default.id}"
+  dimensions = {
+    DBClusterIdentifier = aws_rds_cluster.default.id
     Role                = "READER"
   }
 }
+
diff --git a/main.tf b/main.tf
index 50dbf35..2dc3638 100644
--- a/main.tf
+++ b/main.tf
@@ -162,94 +162,94 @@
 
 // DB Subnet Group creation
 resource "aws_db_subnet_group" "main" {
-  name        = "${var.name}"
+  name        = var.name
   description = "Group of DB subnets"
-  subnet_ids  = ["${var.subnets}"]
+  subnet_ids  = var.subnets
 
-  tags {
-    envname = "${var.envname}"
-    envtype = "${var.envtype}"
+  tags = {
+    envname = var.envname
+    envtype = var.envtype
   }
 }
 
 // Create single DB instance
 resource "aws_rds_cluster_instance" "cluster_instance_0" {
-  identifier                   = "${var.identifier_prefix != "" ? format("%s-node-0", var.identifier_prefix) : format("%s-aurora-node-0", var.envname)}"
-  cluster_identifier           = "${aws_rds_cluster.default.id}"
-  engine                       = "${var.engine}"
-  engine_version               = "${var.engine-version}"
-  instance_class               = "${var.instance_type}"
-  publicly_accessible          = "${var.publicly_accessible}"
-  db_subnet_group_name         = "${aws_db_subnet_group.main.name}"
-  db_parameter_group_name      = "${var.db_parameter_group_name}"
-  preferred_maintenance_window = "${var.preferred_maintenance_window}"
-  apply_immediately            = "${var.apply_immediately}"
-  monitoring_role_arn          = "${join("", aws_iam_role.rds-enhanced-monitoring.*.arn)}"
-  monitoring_interval          = "${var.monitoring_interval}"
-  auto_minor_version_upgrade   = "${var.auto_minor_version_upgrade}"
+  identifier                   = var.identifier_prefix != "" ? format("%s-node-0", var.identifier_prefix) : format("%s-aurora-node-0", var.envname)
+  cluster_identifier           = aws_rds_cluster.default.id
+  engine                       = var.engine
+  engine_version               = var.engine-version
+  instance_class               = var.instance_type
+  publicly_accessible          = var.publicly_accessible
+  db_subnet_group_name         = aws_db_subnet_group.main.name
+  db_parameter_group_name      = var.db_parameter_group_name
+  preferred_maintenance_window = var.preferred_maintenance_window
+  apply_immediately            = var.apply_immediately
+  monitoring_role_arn          = join("", aws_iam_role.rds-enhanced-monitoring.*.arn)
+  monitoring_interval          = var.monitoring_interval
+  auto_minor_version_upgrade   = var.auto_minor_version_upgrade
   promotion_tier               = "0"
-  performance_insights_enabled = "${var.performance_insights_enabled}"
+  performance_insights_enabled = var.performance_insights_enabled
 
-  tags {
-    envname = "${var.envname}"
-    envtype = "${var.envtype}"
+  tags = {
+    envname = var.envname
+    envtype = var.envtype
   }
 }
 
 // Create 'n' number of additional DB instance(s) in same cluster
 resource "aws_rds_cluster_instance" "cluster_instance_n" {
-  depends_on                   = ["aws_rds_cluster_instance.cluster_instance_0"]
-  count                        = "${var.replica_scale_enabled ? var.replica_scale_min : var.replica_count}"
-  engine                       = "${var.engine}"
-  engine_version               = "${var.engine-version}"
-  identifier                   = "${var.identifier_prefix != "" ? format("%s-node-%d", var.identifier_prefix, count.index + 1) : format("%s-aurora-node-%d", var.envname, count.index + 1)}"
-  cluster_identifier           = "${aws_rds_cluster.default.id}"
-  instance_class               = "${var.instance_type}"
-  publicly_accessible          = "${var.publicly_accessible}"
-  db_subnet_group_name         = "${aws_db_subnet_group.main.name}"
-  db_parameter_group_name      = "${var.db_parameter_group_name}"
-  preferred_maintenance_window = "${var.preferred_maintenance_window}"
-  apply_immediately            = "${var.apply_immediately}"
-  monitoring_role_arn          = "${join("", aws_iam_role.rds-enhanced-monitoring.*.arn)}"
-  monitoring_interval          = "${var.monitoring_interval}"
-  auto_minor_version_upgrade   = "${var.auto_minor_version_upgrade}"
-  promotion_tier               = "${count.index + 1}"
-  performance_insights_enabled = "${var.performance_insights_enabled}"
+  depends_on                   = [aws_rds_cluster_instance.cluster_instance_0]
+  count                        = var.replica_scale_enabled ? var.replica_scale_min : var.replica_count
+  engine                       = var.engine
+  engine_version               = var.engine-version
+  identifier                   = var.identifier_prefix != "" ? format("%s-node-%d", var.identifier_prefix, count.index + 1) : format("%s-aurora-node-%d", var.envname, count.index + 1)
+  cluster_identifier           = aws_rds_cluster.default.id
+  instance_class               = var.instance_type
+  publicly_accessible          = var.publicly_accessible
+  db_subnet_group_name         = aws_db_subnet_group.main.name
+  db_parameter_group_name      = var.db_parameter_group_name
+  preferred_maintenance_window = var.preferred_maintenance_window
+  apply_immediately            = var.apply_immediately
+  monitoring_role_arn          = join("", aws_iam_role.rds-enhanced-monitoring.*.arn)
+  monitoring_interval          = var.monitoring_interval
+  auto_minor_version_upgrade   = var.auto_minor_version_upgrade
+  promotion_tier               = count.index + 1
+  performance_insights_enabled = var.performance_insights_enabled
 
-  tags {
-    envname = "${var.envname}"
-    envtype = "${var.envtype}"
+  tags = {
+    envname = var.envname
+    envtype = var.envtype
   }
 }
 
 // Create DB Cluster
 resource "aws_rds_cluster" "default" {
-  cluster_identifier = "${var.identifier_prefix != "" ? format("%s-cluster", var.identifier_prefix) : format("%s-aurora-cluster", var.envname)}"
-  availability_zones = ["${var.azs}"]
-  engine             = "${var.engine}"
+  cluster_identifier = var.identifier_prefix != "" ? format("%s-cluster", var.identifier_prefix) : format("%s-aurora-cluster", var.envname)
+  availability_zones = var.azs
+  engine             = var.engine
 
-  engine_version                  = "${var.engine-version}"
-  master_username                 = "${var.username}"
-  master_password                 = "${var.password}"
+  engine_version                  = var.engine-version
+  master_username                 = var.username
+  master_password                 = var.password
   final_snapshot_identifier       = "${var.final_snapshot_identifier}-${random_id.server.hex}"
-  skip_final_snapshot             = "${var.skip_final_snapshot}"
-  backup_retention_period         = "${var.backup_retention_period}"
-  preferred_backup_window         = "${var.preferred_backup_window}"
-  preferred_maintenance_window    = "${var.preferred_maintenance_window}"
-  port                            = "${var.port}"
-  db_subnet_group_name            = "${aws_db_subnet_group.main.name}"
-  vpc_security_group_ids          = ["${var.security_groups}"]
-  snapshot_identifier             = "${var.snapshot_identifier}"
-  storage_encrypted               = "${var.storage_encrypted}"
-  apply_immediately               = "${var.apply_immediately}"
-  db_cluster_parameter_group_name = "${var.db_cluster_parameter_group_name}"
-  deletion_protection             = "${var.deletion_protection}"
+  skip_final_snapshot             = var.skip_final_snapshot
+  backup_retention_period         = var.backup_retention_period
+  preferred_backup_window         = var.preferred_backup_window
+  preferred_maintenance_window    = var.preferred_maintenance_window
+  port                            = var.port
+  db_subnet_group_name            = aws_db_subnet_group.main.name
+  vpc_security_group_ids          = var.security_groups
+  snapshot_identifier             = var.snapshot_identifier
+  storage_encrypted               = var.storage_encrypted
+  apply_immediately               = var.apply_immediately
+  db_cluster_parameter_group_name = var.db_cluster_parameter_group_name
+  deletion_protection             = var.deletion_protection
 }
 
 // Geneate an ID when an environment is initialised
 resource "random_id" "server" {
   keepers = {
-    id = "${aws_db_subnet_group.main.name}"
+    id = aws_db_subnet_group.main.name
   }
 
   byte_length = 8
@@ -268,30 +268,30 @@ data "aws_iam_policy_document" "monitoring-rds-assume-role-policy" {
 }
 
 resource "aws_iam_role" "rds-enhanced-monitoring" {
-  count              = "${var.monitoring_interval > 0 ? 1 : 0}"
+  count              = var.monitoring_interval > 0 ? 1 : 0
   name_prefix        = "rds-enhanced-mon-${var.envname}-"
-  assume_role_policy = "${data.aws_iam_policy_document.monitoring-rds-assume-role-policy.json}"
+  assume_role_policy = data.aws_iam_policy_document.monitoring-rds-assume-role-policy.json
 }
 
 resource "aws_iam_role_policy_attachment" "rds-enhanced-monitoring-policy-attach" {
-  count      = "${var.monitoring_interval > 0 ? 1 : 0}"
-  role       = "${aws_iam_role.rds-enhanced-monitoring.name}"
+  count      = var.monitoring_interval > 0 ? 1 : 0
+  role       = aws_iam_role.rds-enhanced-monitoring[0].name
   policy_arn = "arn:aws:iam::aws:policy/service-role/AmazonRDSEnhancedMonitoringRole"
 }
 
 // Autoscaling
 resource "aws_appautoscaling_target" "autoscaling" {
-  count              = "${var.replica_scale_enabled ? 1 : 0}"
-  max_capacity       = "${var.replica_scale_max}"
-  min_capacity       = "${var.replica_scale_min}"
+  count              = var.replica_scale_enabled ? 1 : 0
+  max_capacity       = var.replica_scale_max
+  min_capacity       = var.replica_scale_min
   resource_id        = "cluster:${aws_rds_cluster.default.cluster_identifier}"
   scalable_dimension = "rds:cluster:ReadReplicaCount"
   service_namespace  = "rds"
 }
 
 resource "aws_appautoscaling_policy" "autoscaling" {
-  count              = "${var.replica_scale_enabled ? 1 : 0}"
-  depends_on         = ["aws_appautoscaling_target.autoscaling"]
+  count              = var.replica_scale_enabled ? 1 : 0
+  depends_on         = [aws_appautoscaling_target.autoscaling]
   name               = "target-metric"
   policy_type        = "TargetTrackingScaling"
   resource_id        = "cluster:${aws_rds_cluster.default.cluster_identifier}"
@@ -303,8 +303,9 @@ resource "aws_appautoscaling_policy" "autoscaling" {
       predefined_metric_type = "RDSReaderAverageCPUUtilization"
     }
 
-    scale_in_cooldown  = "${var.replica_scale_in_cooldown}"
-    scale_out_cooldown = "${var.replica_scale_out_cooldown}"
-    target_value       = "${var.replica_scale_cpu}"
+    scale_in_cooldown  = var.replica_scale_in_cooldown
+    scale_out_cooldown = var.replica_scale_out_cooldown
+    target_value       = var.replica_scale_cpu
   }
 }
+
diff --git a/outputs.tf b/outputs.tf
index ac89aa7..a92e065 100644
--- a/outputs.tf
+++ b/outputs.tf
@@ -1,24 +1,25 @@
 // The 'writer' endpoint for the cluster
 output "cluster_endpoint" {
-  value = "${aws_rds_cluster.default.endpoint}"
+  value = aws_rds_cluster.default.endpoint
 }
 
 // Comma separated list of all DB instance endpoints running in cluster
 output "all_instance_endpoints_list" {
-  value = ["${aws_rds_cluster_instance.cluster_instance_0.endpoint}", "${aws_rds_cluster_instance.cluster_instance_n.*.endpoint}"]
+  value = [aws_rds_cluster_instance.cluster_instance_0.endpoint, aws_rds_cluster_instance.cluster_instance_n.*.endpoint]
 }
 
 // A read-only endpoint for the Aurora cluster, automatically load-balanced across replicas
 output "reader_endpoint" {
-  value = "${aws_rds_cluster.default.reader_endpoint}"
+  value = aws_rds_cluster.default.reader_endpoint
 }
 
 // Cluster ARN - can use when defining centralised backup
 output "cluster_arn" {
-  value = "${aws_rds_cluster.default.arn}"
+  value = aws_rds_cluster.default.arn
 }
 
 // Cluster ID - useful to any resources requiring cluster's ID, e.g. rds_cluster_role_association
 output "cluster_id" {
-  value = "${aws_rds_cluster.default.id}"
-}
\ No newline at end of file
+  value = aws_rds_cluster.default.id
+}
+
diff --git a/variables.tf b/variables.tf
index 297acbb..9d2f77f 100644
--- a/variables.tf
+++ b/variables.tf
@@ -1,53 +1,53 @@
 variable "name" {
-  type        = "string"
+  type        = string
   description = "Name given to DB subnet group"
 }
 
 variable "subnets" {
-  type        = "list"
+  type        = list(string)
   description = "List of subnet IDs to use"
 }
 
 variable "envname" {
-  type        = "string"
+  type        = string
   description = "Environment name (eg,test, stage or prod)"
 }
 
 variable "envtype" {
-  type        = "string"
+  type        = string
   description = "Environment type (eg,prod or nonprod)"
 }
 
 variable "identifier_prefix" {
-  type        = "string"
+  type        = string
   default     = ""
   description = "Prefix for cluster and instance identifier"
 }
 
 variable "azs" {
-  type        = "list"
+  type        = list(string)
   description = "List of AZs to use"
 }
 
 variable "replica_count" {
-  type        = "string"
+  type        = string
   default     = "0"
   description = "Number of reader nodes to create.  If `replica_scale_enable` is `true`, the value of `replica_scale_min` is used instead."
 }
 
 variable "security_groups" {
-  type        = "list"
+  type        = list(string)
   description = "VPC Security Group IDs"
 }
 
 variable "instance_type" {
-  type        = "string"
+  type        = string
   default     = "db.t2.small"
   description = "Instance type to use"
 }
 
 variable "publicly_accessible" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "Whether the DB should have a public IP address"
 }
@@ -58,174 +58,175 @@ variable "username" {
 }
 
 variable "password" {
-  type        = "string"
+  type        = string
   description = "Master DB password"
 }
 
 variable "final_snapshot_identifier" {
-  type        = "string"
+  type        = string
   default     = "final"
   description = "The name to use when creating a final snapshot on cluster destroy, appends a random 8 digits to name to ensure it's unique too."
 }
 
 variable "skip_final_snapshot" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "Should a final snapshot be created on cluster destroy"
 }
 
 variable "backup_retention_period" {
-  type        = "string"
+  type        = string
   default     = "7"
   description = "How long to keep backups for (in days)"
 }
 
 variable "preferred_backup_window" {
-  type        = "string"
+  type        = string
   default     = "02:00-03:00"
   description = "When to perform DB backups"
 }
 
 variable "preferred_maintenance_window" {
-  type        = "string"
+  type        = string
   default     = "sun:05:00-sun:06:00"
   description = "When to perform DB maintenance"
 }
 
 variable "port" {
-  type        = "string"
+  type        = string
   default     = "3306"
   description = "The port on which to accept connections"
 }
 
 variable "apply_immediately" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "Determines whether or not any DB modifications are applied immediately, or during the maintenance window"
 }
 
 variable "monitoring_interval" {
-  type        = "string"
+  type        = string
   default     = 0
   description = "The interval (seconds) between points when Enhanced Monitoring metrics are collected"
 }
 
 variable "auto_minor_version_upgrade" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "Determines whether minor engine upgrades will be performed automatically in the maintenance window"
 }
 
 variable "db_parameter_group_name" {
-  type        = "string"
+  type        = string
   default     = "default.aurora5.6"
   description = "The name of a DB parameter group to use"
 }
 
 variable "db_cluster_parameter_group_name" {
-  type        = "string"
+  type        = string
   default     = "default.aurora5.6"
   description = "The name of a DB Cluster parameter group to use"
 }
 
 variable "deletion_protection" {
-  type        = "string"
+  type        = string
   default     = "true"
   description = "If the DB instance should have deletion protection enabled. The database can't be deleted when this value is set to true."
 }
 
 variable "snapshot_identifier" {
-  type        = "string"
+  type        = string
   default     = ""
   description = "DB snapshot to create this database from"
 }
 
 variable "storage_encrypted" {
-  type        = "string"
+  type        = string
   default     = "true"
   description = "Specifies whether the underlying storage layer should be encrypted"
 }
 
 variable "cw_alarms" {
-  type        = "string"
+  type        = string
   default     = false
   description = "Whether to enable CloudWatch alarms - requires `cw_sns_topic` is specified"
 }
 
 variable "cw_sns_topic" {
-  type        = "string"
+  type        = string
   default     = "false"
   description = "An SNS topic to publish CloudWatch alarms to"
 }
 
 variable "cw_max_conns" {
-  type        = "string"
+  type        = string
   default     = "500"
   description = "Connection count beyond which to trigger a CloudWatch alarm"
 }
 
 variable "cw_max_cpu" {
-  type        = "string"
+  type        = string
   default     = "85"
   description = "CPU threshold above which to alarm"
 }
 
 variable "cw_max_replica_lag" {
-  type        = "string"
+  type        = string
   default     = "2000"
   description = "Maximum Aurora replica lag in milliseconds above which to alarm"
 }
 
 variable "engine" {
-  type        = "string"
+  type        = string
   default     = "aurora"
   description = "Aurora database engine type, currently aurora, aurora-mysql or aurora-postgresql"
 }
 
 variable "engine-version" {
-  type        = "string"
+  type        = string
   default     = "5.6.10a"
   description = "Aurora database engine version."
 }
 
 variable "replica_scale_enabled" {
-  type        = "string"
+  type        = string
   default     = false
   description = "Whether to enable autoscaling for RDS Aurora (MySQL) read replicas"
 }
 
 variable "replica_scale_max" {
-  type        = "string"
+  type        = string
   default     = "0"
   description = "Maximum number of replicas to allow scaling for"
 }
 
 variable "replica_scale_min" {
-  type        = "string"
+  type        = string
   default     = "2"
   description = "Maximum number of replicas to allow scaling for"
 }
 
 variable "replica_scale_cpu" {
-  type        = "string"
+  type        = string
   default     = "70"
   description = "CPU usage to trigger autoscaling at"
 }
 
 variable "replica_scale_in_cooldown" {
-  type        = "string"
+  type        = string
   default     = "300"
   description = "Cooldown in seconds before allowing further scaling operations after a scale in"
 }
 
 variable "replica_scale_out_cooldown" {
-  type        = "string"
+  type        = string
   default     = "300"
   description = "Cooldown in seconds before allowing further scaling operations after a scale out"
 }
 
 variable "performance_insights_enabled" {
-  type        = "string"
+  type        = string
   default     = false
   description = "Whether to enable Performance Insights"
 }
+
diff --git a/versions.tf b/versions.tf
new file mode 100644
index 0000000..ac97c6a
--- /dev/null
+++ b/versions.tf
@@ -0,0 +1,4 @@
+
+terraform {
+  required_version = ">= 0.12"
+}