You can call DescribeValidDBInstanceModifications to learn what modifications you can make to your DB instance. You can use this information when you call ModifyDBInstance .
See also: AWS API Documentation
See ‘aws help’ for descriptions of global parameters.
  describe-valid-db-instance-modifications
--db-instance-identifier <value>
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]
[--cli-auto-prompt <value>]
--db-instance-identifier (string)
The customer identifier or the ARN of your DB instance.
--cli-input-json | --cli-input-yaml (string)
Reads arguments from the JSON string provided. The JSON string follows the format provided by --generate-cli-skeleton. If other arguments are provided on the command line, those values will override the JSON-provided values. It is not possible to pass arbitrary binary values using a JSON-provided value as the string will be taken literally. This may not be specified along with --cli-input-yaml.
--generate-cli-skeleton (string)
Prints a JSON skeleton to standard output without sending an API request. If provided with no value or the value input, prints a sample input JSON that can be used as an argument for --cli-input-json. Similarly, if provided yaml-input it will print a sample input YAML that can be used with --cli-input-yaml. If provided with the value output, it validates the command inputs and returns a sample output JSON for that command.
--cli-auto-prompt (boolean)
Automatically prompt for CLI input parameters.
See ‘aws help’ for descriptions of global parameters.
To describe valid modifications for a DB instance
The following describe-valid-db-instance-modifications example retrieves details about the valid modifications for the specified DB instance.
aws rds describe-valid-db-instance-modifications \
    --db-instance-identifier test-instance
Output:
{
    "ValidDBInstanceModificationsMessage": {
        "ValidProcessorFeatures": [],
        "Storage": [
            {
                "StorageSize": [
                    {
                        "Step": 1,
                        "To": 20,
                        "From": 20
                    },
                    {
                        "Step": 1,
                        "To": 6144,
                        "From": 22
                    }
                ],
                "ProvisionedIops": [
                    {
                        "Step": 1,
                        "To": 0,
                        "From": 0
                    }
                ],
                "IopsToStorageRatio": [
                    {
                        "To": 0.0,
                        "From": 0.0
                    }
                ],
                "StorageType": "gp2"
            },
            {
                "StorageSize": [
                    {
                        "Step": 1,
                        "To": 6144,
                        "From": 100
                    }
                ],
                "ProvisionedIops": [
                    {
                        "Step": 1,
                        "To": 40000,
                        "From": 1000
                    }
                ],
                "IopsToStorageRatio": [
                    {
                        "To": 50.0,
                        "From": 1.0
                    }
                ],
                "StorageType": "io1"
            },
            {
                "StorageSize": [
                    {
                        "Step": 1,
                        "To": 20,
                        "From": 20
                    },
                    {
                        "Step": 1,
                        "To": 3072,
                        "From": 22
                    }
                ],
                "ProvisionedIops": [
                    {
                        "Step": 1,
                        "To": 0,
                        "From": 0
                    }
                ],
                "IopsToStorageRatio": [
                    {
                        "To": 0.0,
                        "From": 0.0
                    }
                ],
                "StorageType": "magnetic"
            }
        ]
    }
}
ValidDBInstanceModificationsMessage -> (structure)
Information about valid modifications that you can make to your DB instance. Contains the result of a successful call to the
DescribeValidDBInstanceModificationsaction. You can use this information when you callModifyDBInstance.Storage -> (list)
Valid storage options for your DB instance.
(structure)
Information about valid modifications that you can make to your DB instance. Contains the result of a successful call to the
DescribeValidDBInstanceModificationsaction.StorageType -> (string)
The valid storage types for your DB instance. For example, gp2, io1.
StorageSize -> (list)
The valid range of storage in gibibytes. For example, 100 to 16384.
(structure)
A range of integer values.
From -> (integer)
The minimum value in the range.
To -> (integer)
The maximum value in the range.
Step -> (integer)
The step value for the range. For example, if you have a range of 5,000 to 10,000, with a step value of 1,000, the valid values start at 5,000 and step up by 1,000. Even though 7,500 is within the range, it isn’t a valid value for the range. The valid values are 5,000, 6,000, 7,000, 8,000…
ProvisionedIops -> (list)
The valid range of provisioned IOPS. For example, 1000-20000.
(structure)
A range of integer values.
From -> (integer)
The minimum value in the range.
To -> (integer)
The maximum value in the range.
Step -> (integer)
The step value for the range. For example, if you have a range of 5,000 to 10,000, with a step value of 1,000, the valid values start at 5,000 and step up by 1,000. Even though 7,500 is within the range, it isn’t a valid value for the range. The valid values are 5,000, 6,000, 7,000, 8,000…
IopsToStorageRatio -> (list)
The valid range of Provisioned IOPS to gibibytes of storage multiplier. For example, 3-10, which means that provisioned IOPS can be between 3 and 10 times storage.
(structure)
A range of double values.
From -> (double)
The minimum value in the range.
To -> (double)
The maximum value in the range.
SupportsStorageAutoscaling -> (boolean)
Whether or not Amazon RDS can automatically scale storage for DB instances that use the new instance class.
ValidProcessorFeatures -> (list)
Valid processor features for your DB instance.
(structure)
Contains the available processor feature information for the DB instance class of a DB instance.
For more information, see Configuring the Processor of the DB Instance Class in the Amazon RDS User Guide.
Name -> (string)
The name of the processor feature. Valid names are
coreCountandthreadsPerCore.DefaultValue -> (string)
The default value for the processor feature of the DB instance class.
AllowedValues -> (string)
The allowed values for the processor feature of the DB instance class.