RDS Cluster and RDS instance should have backup retention longer than default 1 day

Explanation

RDS backup retention for clusters defaults to 1 day, this may not be enough to identify and respond to an issue. Backup retention periods should be set to a period that is a balance on cost and limiting risk.

Possible Impact

Potential loss of data and short opportunity for recovery

Suggested Resolution

Explicitly set the retention period to greater than the default

Insecure Example

The following example will fail the aws-rds-backup-retention-specified check.

resource "aws_db_instance" "bad_example" {
	allocated_storage    = 10
	engine               = "mysql"
	engine_version       = "5.7"
	instance_class       = "db.t3.micro"
	name                 = "mydb"
	username             = "foo"
	password             = "foobarbaz"
	parameter_group_name = "default.mysql5.7"
	skip_final_snapshot  = true
}

resource "aws_rds_cluster" "bad_example" {
	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"
	preferred_backup_window = "07:00-09:00"
  }

Secure Example

The following example will pass the aws-rds-backup-retention-specified check.

resource "aws_rds_cluster" "good_example" {
	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"
	backup_retention_period = 5
	preferred_backup_window = "07:00-09:00"
  }

  resource "aws_db_instance" "good_example" {
	allocated_storage    = 10
	engine               = "mysql"
	engine_version       = "5.7"
	instance_class       = "db.t3.micro"
	name                 = "mydb"
	username             = "foo"
	password             = "foobarbaz"
	parameter_group_name = "default.mysql5.7"
	backup_retention_period = 5
	skip_final_snapshot  = true
}

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