How to make the allowed Values of a parameter depend on the selected value of another parameter in AWS Cloudformarion

user_13566251 0
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I am very new to aws Cloud and CloudFormation. I am trying to write a CloudFormation Template where a user can choose the DB Engine through a parameter. Depending on the choice made by the user I would like the instance type to change accordingly. For example: Say part of my template looks like this:

Parameters:
Engine:
    Default: sqlserver-ex
    Type: String
    AllowedValues:
      - sqlserver-se
      - sqlserver-ex
      - sqlserver-ee
DatabaseInstanceType:
    Default: db.t3.small
    AllowedValues:
      - db.t2.micro
      - db.t2.small
      - db.t2.medium
      - db.t2.large
      - db.t2.xlarge

When the user chooses the sqlserver-ex I only want the user to be able to choose an InstanceType like 

db.t2.micro
dbt2.medium
db.t3.small
db.t3.xlarge
db.t2.micro
dbt2.medium
db.t3.small
db.t3.xlarge

Is this posible? Is it also posible to use that technique multiple times in a template?

I have searched for a solution for this for a few days with no luck and decided to ask the more advanced developers. I hope that someone can clear this up for me. Thanks in advance.

amazon-cloudformation amazon-web-services
2 Answers
user_41228490

Update

If the cross-parameter validation solution (provided by @Pat Myron https://stackoverflow.com/a/61874910/842075) works then of course it's better to use that solution.

Original answer

Yes, possible but with tricks. Basically the trick is to replace two parameters with one parameter:

Parameters:
  EngineAndInstanceType:
    Default: sqlserver-ex/db.t3.small
    Type: String
    AllowedValues:
      - sqlserver-se/db.t2.micro
      - sqlserver-se/db.t2.small
      - sqlserver-se/db.t2.medium

      - sqlserver-ex/db.t3.micro
      - sqlserver-ex/db.t3.small
      - sqlserver-ex/db.t3.medium

      - sqlserver-ee/db.t2.large
      - sqlserver-ee/db.t2.xlarge

this of course will disable you from simply !Referencing engine and instance type later in template. You will have to use combination of !Select and !Split functions to be able to use one parameter in two different places:

Resources:
  MyDB:
    Type: 'AWS::RDS::DBInstance'
    Properties:
      Engine: !Select [0, !Split ["/", !Ref EngineAndInstanceType]]
      DBInstanceClass: !Select [1, !Split ["/", !Ref EngineAndInstanceType]]
user_8420750
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