List of RDS instances in cloudformation template as parameters

Question

Hello ,

How can I get dynamically list of RDS instances IDs to use it as parameter in cloudformation template ?

Something like below but generated dynamically  :

```
 Parameters:
  RDSInstanceIDParameter:
    Type: String
    Default: rds-a1
    AllowedValues:
      - !Select [ "1", [ "rds-a1", "rds-a2", "rds-a3", "rds-a4" ] ]
      - !Select [ "2", [ "rds-a1", "rds-a2", "rds-a3", "rds-a4" ] ]
      - !Select [ "3", [ "rds-a1", "rds-a2", "rds-a3", "rds-a4" ] ]
    Description: Enter logical name ID of RDS which You want to integrate with EFS .
```

How can I  get  list of  RDS ids    etc. " [ "rds-a1", "rds-a2", "rds-a3", "rds-a4" ] ]"

It is possible to use some inline javascript/python code here ? What are my options ?

Giovanni Lauria · Answer

Hello, I think this can help you in obtaining the dynamic list.

- Create an SSM parameter (e.g., `/myapp/rds_instance_ids`) of type `String` to store the list of RDS instance IDs.
- Develop a Lambda function with permissions to call the `ssm:GetParametersByPath` API.
- Write code in the Lambda function to fetch the list of RDS instance IDs and update the SSM parameter.
- Configure a CloudWatch Event rule to trigger the Lambda function at regular intervals (e.g., every hour).
- Define a parameter in the CloudFormation template (e.g., `RDSInstanceIDParameter`) with `AllowedValues` referencing the SSM parameter created in step 1.

CloudFormation template will dynamically fetch the latest list of RDS instance IDs from the SSM parameter upon deploy of the stack.
Hope This Helps

List of RDS instances in cloudformation template as parameters

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