def validate_target_types(target_type):
    """
    Target types validation rule.
    Property: SecretTargetAttachment.TargetType
    """

    VALID_TARGET_TYPES = (
        "AWS::RDS::DBInstance",
        "AWS::RDS::DBCluster",
        "AWS::Redshift::Cluster",
        "AWS::DocDB::DBInstance",
        "AWS::DocDB::DBCluster",
    )

    if target_type not in VALID_TARGET_TYPES:
        raise ValueError(
            "Target type must be one of : %s" % ", ".join(VALID_TARGET_TYPES)
        )
    return target_type