Acessing the 'DistributionConfig' of the 'CfnDistribution_' throws an error

[McDoit]

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• I'm submitting a ...

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

• What is the current behavior?
  If the current behavior is a 🪲bug🪲: Please provide the steps to reproduce

Create a new CloudFrontWebDistribution, var cf = new CloudFrontWebDistribution
Access the underlying CfnDistribution_ with var cfd = cf.Node.FindChild("CFDistribution") as CfnDistribution_;
Acessing the DistributionConfig of the CfnDistribution_ throws an error:

Got 'undefined' for non-optional instance of {"abstract":true,"docs":{"remarks":"If this returns an empty array the stack will not be attached.","stability":"stable","summary":"The creation stack of this resolvable which will be appended to errors thrown during resolution."},"immutable":true,"locationInModule":{"filename":"lib/resolvable.ts","line":38},"name":"creationStack","type":{"collection":{"elementtype":{"primitive":"string"},"kind":"array"}}}

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

To be able to see the DistributionConfig of the CfnDistribution_

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

I was trying to work around other bugs in the CloudFrontWebDistribution by accessing the DistributionConfig to modify and add it back as overrides

• Please tell us about your environment:

  • CDK CLI Version: 0.39
  • Module Version: 0.39
  • OS: [Windows 10]
  • Language: [C#]

• 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)
  Stacktrace:

Got 'undefined' for non-optional instance of {"abstract":true,"docs":{"remarks":"If this returns an empty array the stack will not be attached.","stability":"stable","summary":"The creation stack of this resolvable which will be appended to errors thrown during resolution."},"immutable":true,"locationInModule":{"filename":"lib/resolvable.ts","line":38},"name":"creationStack","type":{"collection":{"elementtype":{"primitive":"string"},"kind":"array"}}}

   at Amazon.JSII.Runtime.Services.Client.TryDeserialize[TResponse](String responseJson)
   at Amazon.JSII.Runtime.Services.Client.ReceiveResponse[TResponse]()
   at Amazon.JSII.Runtime.Deputy.DeputyBase.GetPropertyCore[T](JsiiPropertyAttribute propertyAttribute, Func`2 getFunc)

[RomainMuller]

Does this problem still exist with cdk >= 1.0.0?

[McDoit]

Still get the same error message in 1.1.0-devpreview

[McDoit]

Still get the same error in 1.4-devpreview

[McDoit]

Here is a samll repro:

public class ReproCloudFrontStack : Stack
        {
            public ReproCloudFrontStack(Construct scope, string name, IStackProps props) : base(scope, name, props)
            {
                var cf = new CloudFrontWebDistribution(this, "MyDistribution", new CloudFrontWebDistributionProps
                {
                    HttpVersion = HttpVersion.HTTP2,
                    PriceClass = PriceClass.PRICE_CLASS_ALL,
                    OriginConfigs = new ISourceConfiguration[]
                        {
                            new SourceConfiguration
                            {
                                CustomOriginSource = new CustomOriginConfig
                                {
                                    DomainName = "example.com",
                                    HttpPort = 80,
                                    OriginProtocolPolicy = OriginProtocolPolicy.HTTP_ONLY,
                                },
                               Behaviors = new IBehavior[]
                               {
                                   new Behavior
                                   {
                                       AllowedMethods = CloudFrontAllowedMethods.ALL,
                                       Compress = true,
                                       IsDefaultBehavior = true
                                   }
                               }
                            }
                        }
                });

                var cfd = cf.Node.FindChild("CFDistribution") as CfnDistribution;

                var dcp = cfd.DistributionConfig as CfnDistribution.DistributionConfigProperty;

                var ir = cfd.DistributionConfig as IIResolvable;

                Console.WriteLine(ir.CreationStack);
            }
        }

cdp is null as DistributionConfig can't be resolved into CfnDistribution.DistributionConfigProperty

But casting DistributionConfig into a IIResolvable will make the ir.CreationStack throw the error

[McDoit]

Still an issue with CDK 1.8 and JSII 0.17 sadly

[McDoit]

Still an issue with CDK 1.10.1 and JSII 0.18 sadly

[RomainMuller]

Alright - thanks for providing the repro code. We'll be having a look into the cause of this (hopefully) shortly, and will update the issue with our findings!

[McDoit]

Perfect, thank you @RomainMuller!

These two are a bit related, at least the first, and might be beneficial to work on at the same time?

#3281
#3282

[RomainMuller]

Sorry it took me so long to come back. I'm looking into testing your reproduction against the current HEAD of aws/jsii, in hopes that the last kernel bug I fixed was the cause of this issue (I'm pretty optimistic!)

[McDoit]

No worries

Just tried the latest CDK with JSII 0.19 with no change
With JSII 0.20 and Visual studio 2019 i get a new error:
Unhandled exception. System.MissingMethodException: .ctor
I guess i should file that as a new issue

As a side note i get the following erro in my full code when using alias config and a ACM cert:
Unhandled Exception: Amazon.JSII.Runtime.JsiiException: acmCertificate certficate must be in the us-east-1 region, got eu-west-1
even if i specify "us-east-1" in the DnsValidatedCertificate i setup in the stack

[RomainMuller]

Yeah the problem is our dependencies are currently not modeled currently and this allowed an incompatible JSII runtime to be picked up by your install. We are going to release a fixed version very soon.

[McDoit]

Just tested this again, no error this time, but the object returned cant be cast into a DistributionConfigProperty, it returns a Amazon.JSII.Runtime.Deputy.AnonymousObject instead

It throws this:

System.InvalidCastException: 'Unable to cast object of type 'Amazon.JSII.Runtime.Deputy.AnonymousObject' to type 'DistributionConfigProperty'.'

[McDoit]

@RomainMuller is it possible to open this one up again, as it is still not fixed?

[njlynch]

I verified; just reproduced the above errors (Amazon.JSII.Runtime.Deputy.AnonymousObject/NPE) on CDK 1.68.0.

[McDoit]

@njlynch Maybe unassign @RomainMuller so someone else can take a look?

[RomainMuller]

The issue is that cfd.DistributionConfig is originally typed as a union, which prevents the .NET code from having enough type information to systematically back this cast. We'll probably need to offer a separate API to allow for this (one already exists, but it might still not allow what you are trying to do right now -- although it probably can be modified to allow that).

[njlynch]

@McDoit ,

Separate from the underlying issue, I wonder if we can help with anything with the construct library itself. What is it that CloudFront is missing such that you need to resort to these escape hatches and post-creation modifications?

[RomainMuller]

I've created aws/jsii#2192 to introduce an UnsafeCast<T>() method on DeputyBase (the parent class of AnonymousObject) to allow casting to an arbitrary interface type.

This would allow you to write something along the lines of:

var dcp = (cfd.DistributionConfig as DeputyBase).UnsafeCast<CfnDistribution.DistributionConfigProperty>();

Effectively un-blocking your use-case (and other use-cases that involve property overrides with complex/composite properties).

This might become more elegant in the future, as type unions are supported better (more info at aws/aws-cdk-rfcs#193).

[McDoit]

@McDoit ,

Separate from the underlying issue, I wonder if we can help with anything with the construct library itself. What is it that CloudFront is missing such that you need to resort to these escape hatches and post-creation modifications?

Trying to remember it from over a year ago, but I think the reason was to modify some option and naming to convert our existing CF stacks to using the CDK instead. So deploying the same stack name (and resources) but wrap it in the CDK instead.

Main issue there was that replacing the CF distributions as custom domains on them need to be unique, and we didn't want to deal with it manually or have downtime solving it.

[McDoit]

I've created aws/jsii#2192 to introduce an UnsafeCast<T>() method on DeputyBase (the parent class of AnonymousObject) to allow casting to an arbitrary interface type.

This would allow you to write something along the lines of:

var dcp = (cfd.DistributionConfig as DeputyBase).UnsafeCast<CfnDistribution.DistributionConfigProperty>();

Effectively un-blocking your use-case (and other use-cases that involve property overrides with complex/composite properties).

This might become more elegant in the future, as type unions are supported better (more info at aws/aws-cdk-rfcs#193).

I tried it with CDK 1.70 and JSII 1.14, but I got the following error running the repro stack above:
System.InvalidCastException: 'Unable to cast Amazon.JSII.Runtime.Deputy.AnonymousObject into Amazon.CDK.AWS.CloudFront.CfnDistribution+DistributionConfigProperty'

[RomainMuller]

Hmmm. Thanks for reporting. I'll have a look into it.

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