go: How to map Condition function return to specific type

[xrn]

Affected Languages

• [ x] Go

General Information

• JSII Version: v1.28.0
• Platform: SMP Debian 5.10.28-1 (2021-04-09) x86_64 GNU/Linux

The Question

I spent this long time and can not find an answer anywhere because go in still in development preview. I have code like

	// The code that defines your stack goes here
	lambdaFnA := awslambda.NewFunction(stack, jsii.String("Singleton"), &awslambda.FunctionProps{
		Code:    awslambda.NewAssetCode(jsii.String("lambda"), nil),
		Handler: jsii.String("handler.main"),
		Timeout: awscdk.Duration_Seconds(jsii.Number(300)),
		Runtime: awslambda.Runtime_PYTHON_3_6(),
	})

	lambdaFnB := awslambda.NewFunction(stack, jsii.String("Singleton"), &awslambda.FunctionProps{
		Code:    awslambda.NewAssetCode(jsii.String("lambda"), nil),
		Handler: jsii.String("handler.main"),
		Timeout: awscdk.Duration_Seconds(jsii.Number(300)),
		Runtime: awslambda.Runtime_PYTHON_3_6(),
	})

	awscognito.NewUserPool(stack, aws.String("UserPoll"), &awscognito.UserPoolProps{
		UserPoolName: awscdk.Fn_Sub(aws.String("${Environment}-SC-Pool"), nil),
		LambdaTriggers: awscdk.Fn_ConditionIf("Condition",
			&awscognito.UserPoolTriggers{
				PostAuthentication: lambdaFnA,
			},
			&awscognito.UserPoolTriggers{},
		),
	})

Which from perspective Cloudfroamtion should work - I can create if statement for the whole object. But Fn_ConditionIf returns type ICfnConditionExpression and I am expecting &awscognito.UserPoolTriggers - digging in code we can find sth from ts but I am not sure how to map this in go

new sqs.Queue(this, 'MyQueue', {
    queueName: Fn.conditionIf('Condition', 'Hello', 'World').toString()
});

[MrArnoldPalmer]

Hey @xrn, I believe your issue is related to the usage of CFN intrinsics within L2s. This is unrelated to downcasting #2819 I believe.

As you said UserPoolProps LambdaTriggers prop is expected to be *UserPoolTriggers. When using L2 constructs you should just use normal go if/else to perform conditional logic and go string interpolation.

UserPoolName: awscdk.Fn_Sub(aws.String("${Environment}-SC-Pool"), nil),
// should be
UserPoolName: aws.String(fmt.Sprintf("%s-SC-Pool", Environment)),

If you give an example of the condition you're using we may be able to give some more examples.

[xrn]

Normal If will not work here because I need that If in template which will be deployed on multiple env with different parameters. And condition will be cloudformation.condition - https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html like for example

"CreateBucket": {
            "Fn::Not": [
                {
                    "Fn::Equals": [
                        {
                            "Ref": "BucketName"
                        },
                        ""
                    ]
                }
            ]
        },

and then

awscognito.NewUserPool(stack, aws.String("UserPoll"), &awscognito.UserPoolProps{
		UserPoolName: awscdk.Fn_Sub(aws.String("${Environment}-SC-Pool"), nil),
		LambdaTriggers: awscdk.Fn_ConditionIf("CreateBucket",
			&awscognito.UserPoolTriggers{
				PostAuthentication: lambdaFnA,
			},
			&awscognito.UserPoolTriggers{},
		),
	})

From pure cloudformation yaml/json my example is correct I am using it already with goFormation

[xrn]

Example from working Cloudformation template

Conditions:
  CreateWithPreAuthTrigger:
    Fn::Or:
    - Fn::Equals:
      - Ref: Environment
      - PROD
    - Fn::Equals:
      - Ref: Environment
      - STG
  UserPool:
    Properties:
      AutoVerifiedAttributes:
      - email
      DeviceConfiguration:
        DeviceOnlyRememberedOnUserPrompt: true
      EmailVerificationMessage: Your verification code is {####}.
      EmailVerificationSubject: Your verification code
      LambdaConfig:
        Fn::If:
        - CreateWithPreAuthTrigger
        - PreAuthentication:
            Fn::Sub: arn:aws:lambda:${AWS::Region}:${AWS::AccountId}:function:${Environment}-PreAuthentication-Lambda
        - {}
      MfaConfiguration: "OFF"
      Policies:
        PasswordPolicy:
          MinimumLength: 8
          RequireLowercase: true
          RequireNumbers: true
          TemporaryPasswordValidityDays: 7
      UserPoolName:
        Fn::Sub: ${Environment}-SC-Pool
      UsernameAttributes:
      - email
    Type: AWS::Cognito::UserPool

My team is using conditions on objects in few other places like this

[xrn]

@MrArnoldPalmer any chance for help with this?

[MrArnoldPalmer]

@xrn I'll have to spend some time working through your specific examples which I don't have at the moment, but I would encourage you again to forget about what your existing cloudformation templates look like and just treat your CDK app like a normal program, and not a static template.

You can pass in your environment to your cdk app and then switch, if/else, etc based on that value and change what resources are created and how. I don't think this is a go specific problem, but I'll look into it more when I have time available so we can provide language specific guidance here if CFN intrinsics are required.

Have you tried using the L1 constructs instead?

[xrn]

Have you tried using the L1 constructs instead?

Tbh I am not sure what it mean

[MrArnoldPalmer]

@xrn sorry for the jargon 😄 . The L1s are the lower level constructs, ones named CfnXxx within each library. For example instead of NewUserPool you can try NewCfnUserPool. The L1's are a 1:1 represenation of the cloudformation APIs whereas the L2s, like UserPool, have some defaults and may build other resources automatically under the hood.

Additionally there are escape hatches that allow you to access the L1's from the L2's and edit any property however you want. There are some issues with these in go that we are currently working on though.

[xrn]

Hi @MrArnoldPalmer I used CfnUserPoolProps with LambdaConfig and looks like I was able to achieve what I need

	awscognito.NewCfnUserPool(stack, aws.String("UserPool"), &awscognito.CfnUserPoolProps{
		UserPoolName: awscdk.Fn_Sub(aws.String("${Environment}-SC-Pool"), nil),
		LambdaConfig: awscdk.Fn_ConditionIf(aws.String("Condition"),
			map[string]interface{}{
				"PostAuthentication": lambdaFn.FunctionArn(),
			},
			map[string]interface{}{},
		),
	})

It is not perfect user experience and there is lack of materials - but at least I was able to generate

UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      LambdaConfig:
        Fn::If:
          - Condition
          - PostAuthentication:
              Fn::GetAtt:
                - Singleton8C7B99F3
                - Arn
          - {}
      UserPoolName:
        Fn::Sub: ${Environment}-SC-Pool
    Metadata:
      aws:cdk:path: LambdaCronStack/UserPool

[MrArnoldPalmer]

@xrn gonna close this for now as it's not a JSII or language specific issue. Reopen in aws/aws-cdk if you want to continue the discussion. Glad you got it resolved for now though!

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