🚢 SSM Parameters

[jamie-lynch]

Many stacks use parameters to allow values to be defined at deploy time. The GuParameter construct, built on top of the CfnParameter, allows these parameters to be defined. It takes a type value as an input, to denote the type of the expected value.

These parameters can either be provided directly or by reference to a path in Parameter Store. Where parameter values are to be resolved from Parameter Store, the type provided should be the type of the expected value wrapped with AWS::SSM::Parameter::Value - e.g. AWS::SSM::Parameter::Value<String>. Any valid type can be provided.

Currently we provide the GuSSMParameter which sets the type to AWS::SSM::Parameter::Value<String>. Clearly this means that only string values can be provided through parameter store without providing the entire type to the GuParameter construct.

Can we do better?!

Option 1

We could rename the GuSSMParameter to GuSSMStringParameter and also provide a number of other helper classes such as GuSSMStringListParameter which would implement the correct type in each case. This is likely to lead to the vast majority of the parameter classes being duplicated however.

Option 2

Provide a GuSSMParameter which takes the value type as a prop and wraps it with AWS::SSM:Parameter::Value for you. For example:

export class GuSSMParameter extends GuParameter {
  constructor(scope: GuStack, id: string, props: GuParameterProps) {
    super(scope, id, {
      ...props,
      type: `AWS::SSM::Parameter::Value<props.type>`,
    });
  }
}

Option 3

For all supported parameters, the construct could take a boolean prop to denote whether the value is provided directly or resolved from parameter store. Using this parameter would then look something like:

new GuSubnetListParameter(this, "SubnetListParameter", { useParameterStore: true }) // type -> AWS::SSM::Parameter::Value<List<AWS::EC2::Subnet::Id>>

new GuSubnetListParameter(this, "SubnetListParameter") // type -> List<AWS::EC2::Subnet::Id>

Option 4

Some other option as-yet-unthought-of option!

[akash1810]

I think generics might be of use here, will need to experiment a little.

[jamie-lynch]

#141 adds SSM support for all parameter constructs extending GuParameter