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Updated README.md to include information about conditionalCreateOnlyP… #148

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Updated README.md to include information about conditionalCreateOnlyP… #148

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Expand Up @@ -34,6 +34,7 @@ Certain properties of a resource are _semantic_ and have special meaning when us
* **`readOnlyProperties`**: A property in the `readOnlyProperties` list cannot be specified by the customer.
* **`writeOnlyProperties`**: A property in the `writeOnlyProperties` cannot be returned in a **READ** or **LIST** request, and can be used to express things like passwords, secrets or other sensitive data.
* **`createOnlyProperties`**: A property in the `createOnlyProperties` cannot be specified in an **UPDATE** request, and can only be specified in a **CREATE** request. Another way to think about this - these are properties which are 'write-once', such as the [`Engine`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-rds-database-instance.html#cfn-rds-dbinstance-engine) property for an [`AWS::RDS::DBInstance`](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-rds-database-instance.html) and if you wish to change such a property on a live resource, you should replace that resource by creating a new instance of the resource and terminating the old one. This is the behaviour CloudFormation follows for all properties documented as _'Update Requires: Replacement'_. An attempt to supply these properties to an **UPDATE** request will produce a runtime error from the handler.
* **`conditionalCreateOnlyProperties`**: A property in the `conditionalCreateOnlyProperties` can only be updated under certain conditions. For example, you can upgrade the engine version of an RDS DBInstance but you cannot downgrade it. When updating this property for a resource in a CloudFormation stack, the resource will be replaced if it cannot be updated.
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I think we need to mention that such properties behave like createOnlyProperties only when specific values are changed. Such scenarios MUST be handled by UpdateHandler throwing NotUpdatable exception

* **`deprecatedProperties`**: A property in the `deprecatedProperties` is not guaranteed to be present in the response from a **READ** request. These fields will still be accepted as input to **CREATE** and **UPDATE** requests however they may be ignored, or converted to new API forms when outbound service calls are made.
* **`replacementStrategy`**: As mentioned above, changing a `createOnlyProperty` requires replacement of the resource by creating a new one and deleting the old one. The default CloudFormation replacement behavior is to create a new resource first, then delete the old resource, so as to avoid any downtime. However, some resources are singleton resources, meaning that only one can exist at a time. In this case, it is not possible to create a second resource first, so CloudFormation must Delete first and then Create. Specify either `create_then_delete` or `delete_then_create`. Default value is `create_then_delete`
* **`taggable`**: [DEPRECATED] ~~A boolean type property which defaults to true, indicating this resource type supports updatable [`tagging property`](https://docs.aws.amazon.com/general/latest/gr/aws_tagging.html). Otherwise, it indicates this resource type does not contain any updatable [`tagging properties`](https://docs.aws.amazon.com/general/latest/gr/aws_tagging.html)~~.
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