fix: prevent creating empty replicas record

[syphernl]

what

• Prevent creating empty DNS replicas record when cluster_size < 1

why

• If the cluster_size = 0 this would result in an attempt to create an empty DNS record, which is not permitted by the Route53 API

references

• Follow-up to changes done in Additional inputs #124

[bridgecrew]

Bridgecrew has found infrastructure configuration errors in this PR ⬇️

[bridgecrew]

  Ensure RDS instances have backup policy
    Resource: aws_rds_cluster.secondary | ID: BC_AWS_GENERAL_46

How to Fix

resource "aws_rds_cluster" "test" {
  ...
+ backup_retention_period = 35
}

Description

This check examines the attribute **backup_retention_period** this should have a value 1-35, and checks if its set to 0 which would disable the backup.

This check is currently under review and maybe suppressed in future releases.

Dependent Resources

Path	Resource	Connecting Attribute
/main.tf	aws_rds_cluster_instance.default	depends_on
cluster	coalesce(join(, aws_rds_cluster.primary.*.id), join(, aws_rds_cluster.secondary.*.id))	resource_id

[bridgecrew]

  Ensure Postgres RDS has Query Logging enabled
    Resource: aws_rds_cluster.secondary | ID: BC_AWS_GENERAL_96

Description

TBD Dependent Resources

Path	Resource	Connecting Attribute
/main.tf	aws_rds_cluster_instance.default	depends_on
cluster	coalesce(join(, aws_rds_cluster.primary.*.id), join(, aws_rds_cluster.secondary.*.id))	resource_id

[bridgecrew]

  Ensure RDS clusters have an AWS Backup backup plan
    Resource: aws_rds_cluster.secondary | ID: BC_AWS_GENERAL_49

How to Fix

resource "aws_rds_cluster" "rds_cluster_good" {
  cluster_identifier      = "aurora-cluster-demo"
  engine                  = "aurora-mysql"
  engine_version          = "5.7.mysql_aurora.2.03.2"
  availability_zones      = ["us-west-2a", "us-west-2b", "us-west-2c"]
  database_name           = "mydb"
  master_username         = "foo"
  master_password         = "bar"
}


resource "aws_backup_plan" "example" {
  name = "tf_example_backup_plan"

  rule {
    rule_name         = "tf_example_backup_rule"
    target_vault_name = "vault-name"
    schedule          = "cron(0 12 * * ? *)"
  }
}

resource "aws_backup_selection" "backup_good" {
  iam_role_arn = "arn:partition:service:region:account-id:resource-id"
  name         = "tf_example_backup_selection"
  plan_id      = aws_backup_plan.example.id

  resources = [
    aws_rds_cluster.rds_cluster_good.arn
  ]
}

Description

TBA

Dependent Resources

Path	Resource	Connecting Attribute
/main.tf	aws_rds_cluster_instance.default	depends_on
cluster	coalesce(join(, aws_rds_cluster.primary.*.id), join(, aws_rds_cluster.secondary.*.id))	resource_id

[max-lobur]

/test all

[max-lobur]

Thanks for your PR @syphernl !
I have created #127 to track BridgeCrew.
This PR is good to go!