[apigateway] Add validations to the 'variables' property on Stage resource

[igilham]

• I'm submitting a ...

  • 🪲 bug report
  • 🚀 feature request
  • 📚 construct library gap
  • ☎️ security issue or vulnerability => Please see policy
  • ❓ support request => Please see note at the top of this template.

• What is the current behavior?

API Gateway Stage variables must match a regex to be valid (See the documentation). When adding variables using CDK, this regex is not enforced, so it can synthesize a CloudFormation template that cannot be deployed.

    // const myFunction: IFunction;

    const versionAlias = lambda.Version.fromVersionAttributes(this, 'VersionInfo', {
        lambda: myFunction,
        version: '${stageVariables.lambdaAlias}'
    });

    const api: apiGateway.RestApi = new apiGateway.LambdaRestApi(this, 'RestApi', {
        restApiName: 'my-test-api',
        handler: versionAlias,
        deployOptions: {
          variables: {
            lambdaAlias: myFunction.latestVersion // == '$LATEST'
          }
        }
      });

• What is the expected behavior (or behavior of feature suggested)?

CDK could throw an error if the variable values do not match the regex, preventing invalid templates from being created.

• What is the motivation / use case for changing the behavior or adding this feature?

In a Blue/Green Deployment use case, I might have blue, green and production stages on my RestAPI, using Stage variables to define which Lambda alias each stage integrates with. It is currently illegal to use the $LATEST alias in a Stage variable.

• Please tell us about your environment:

  • CDK CLI Version: 1.3.0
  • Module Version: @aws-cdk/aws-apigateway@1.3.0
  • OS: OSX Mojave 10.14.5
  • Language: TypeScript

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. associated pull-request, stackoverflow, gitter, etc)

[github-actions]

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[igilham]

Perhaps this should be documented as a known limitation if there's not enough interest to work on it?

[github-actions]

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