DocumentDB encryption should use Customer Managed Keys

Explanation

Encryption using AWS keys provides protection for your DocumentDB underlying storage. To increase control of the encryption and manage factors like rotation use customer managed keys.

Possible Impact

Using AWS managed keys does not allow for fine grained control

Suggested Resolution

Enable encryption using customer managed keys

Insecure Example

The following example will fail the aws-documentdb-encryption-customer-key check.

resource "aws_docdb_cluster" "docdb" {
  cluster_identifier      = "my-docdb-cluster"
  engine                  = "docdb"
  master_username         = "foo"
  master_password         = "mustbeeightchars"
  backup_retention_period = 5
  preferred_backup_window = "07:00-09:00"
  skip_final_snapshot     = true
}

Secure Example

The following example will pass the aws-documentdb-encryption-customer-key check.

resource "aws_kms_key" "docdb_encryption" {
	enable_key_rotation = true
}
			
resource "aws_docdb_cluster" "docdb" {
  cluster_identifier      = "my-docdb-cluster"
  engine                  = "docdb"
  master_username         = "foo"
  master_password         = "mustbeeightchars"
  backup_retention_period = 5
  preferred_backup_window = "07:00-09:00"
  skip_final_snapshot     = true
  kms_key_id 			  = aws_kms_key.docdb_encryption.arn
}

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