Updates StringParameter.valueFromLookup with an optional "defaultValue" When specified this value will be used:

• in place of the standard dummyValue
• to signal that an Error should not be raised during synthesis if the parameter is not found in the account.

Test are updated to prove that this works

Issue # (if applicable)

Resolves #7051

There are some closed issues which also benefit from this change:

• SSM: StringParameter.valueFromLookup should return undefined if SSM parameter not available #22064
• SSM StringParameter should query multiple paths #7259

Reason for this change

We have a library which has a fixed set of SSM parameters on which it depends. The values from those parameters are made available as attributes of a custom Stack. We have many users in many different AWS accounts, and not all of the parameters are guaranteed to exist. This is okay. In general, teams would simply not use those values and be happy with that outcome. Unfortunately, CDK crashes when you look up an SSM parameter that does not exist in the account. This is unacceptable.

Description of changes

To address the issue described above, I implemented an optional parameter on the valueFromLookup method: defaultValue. The idea is that if this value is specified, and we fail to look up a parameter in the account, we will return this value and suppress the Error that is currently raised when a parameter is not found.

To implement that functionality, I added a field to the GetContextValueOptions interface which is used to flag that we're not going to raise the error. Then, in valueFromLookup, I set that flag to true if the dummyValue is specified. valueFromLookup then calls ContextProvider.getValue passing along those values.

ContextProvider.getValue is modified so that when it calls stack.reportMissingContextKey it passes a modified set of props which include the defaultValue and the ignoreErrorOnMissingContext flag.

These finally land in the aws-cdk context provider for ssm-parameter. That code has been updated so that if the value is not found in SSM, and we're told to suppress the error, then we'll simply return the defaultValue that was passed in.

Description of how you validated changes

I added a unit tests which covers when the default value is set. I also updated the original unit test as the props now contain some additional field.

I added an integration test which calls valueFromLookup with a defaultValue set and then confirms that no exception is raised and that valueFromLookup returned the defaultValue

NOTE
I considered that the changes made might need to be a part of the cloud-assembly-schema but chose to work around that for now. I'm open to incorporating them there if that's a more correct path.

NOTE 2
I'm unsure about how to update API documentation for this change. This does alter the public API for valueFromLookup and the function doesn't appear to have a proper TSDoc header on it. Please let me know if there's a proper way for me to update the documentation.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license