(aws-cloudfront): Unexpected diffs caused by cloudfront.Function #15523

iliapolo · 2021-07-13T11:41:32Z

Non deterministic auto-generated function name causing unexpected diffs.

Reproduction Steps

Using this code:

new cloudfront.Function(stack, 'Function', {
  code: cloudfront.FunctionCode.fromInline('function handler(event) { return event.request }'),
});

synth and extract the function name
synth again and extract the function name

The function name is different for every synth.

What did you expect to happen?

The function name should be the same.

What actually happened?

Function name changes per synth.

Environment

CDK CLI Version : ALL
Framework Version: 1.109.0
Node.js Version: ALL
OS : ALL
Language (Version): ALL

Other

This happens because of:

aws-cdk/packages/@aws-cdk/aws-cloudfront/lib/function.ts

Lines 178 to 185 in 94f81c4

    
             private generateName(): string { 
        
               const name = Stack.of(this).region + Names.uniqueId(this); 
        
               if (name.length > 64) { 
        
                 return name.substring(0, 32) + name.substring(name.length - 32); 
        
               } 
        
               return name; 
        
             } 
        
           }

Where Stack.of(this).region is an unresolved token that can have a different sequence number every time the program is executed.

A workaround right now would be to provide a name explicitly and not rely on this logic.

Workaround

Provide an explicit name for cloudfront.Function. Using this.node.addr or Node.of(this).addr will return a stable fixed length unique id. Example:

const functionId = `MyFunction${this.node.addr}`;

new cloudfront.Function(stack, functionId, {
  code: cloudfront.FunctionCode.fromInline('function handler(event) { return event.request }'),
  functionName: functionId
});

This is 🐛 Bug Report

The text was updated successfully, but these errors were encountered:

hoegertn · 2021-07-13T11:44:26Z

Shouldn't the region be !Ref AWS::Region in the template and be stable?

eladb · 2021-07-13T12:34:50Z

I would recommend using Node.of(this).addr which returns a stable fixed length unique id

hoegertn · 2021-07-13T12:56:44Z

@njlynch 's wish was to add the region information as CF is a global service. But if this is no longer needed happy to remove it. This would be a breaking change for the implementation afaik.

eladb · 2021-07-13T14:16:12Z

@njlynch 's wish was to add the region information as CF is a global service. But if this is no longer needed happy to remove it. This would be a breaking change for the implementation afaik.

What kind of breaking change?

hoegertn · 2021-07-13T14:23:54Z

If we change the generation of the name it will recreate the CF functions on the next deployment. The name is the physicalName of the function.

eladb · 2021-07-13T14:28:36Z

Will it cause outage or availability risk?

hoegertn · 2021-07-13T14:31:55Z

The ARN will change and this will break CF Distributions using it if not within the same stack. A short outage might as well be a thing as it removes one CFF and then registers the new CFF.

eladb · 2021-07-13T14:35:16Z

I think CFN will first create the new CFF, update the distribution and only then remove the old one (that's how resource replacement works)

hoegertn · 2021-07-13T14:55:29Z

I meant on the distribution. So there might be a time where no CFF is registered.

jogold · 2021-07-14T09:40:08Z

Where Stack.of(this).region is an unresolved token that can have a different sequence number every time the program is executed.

I don't understand how it can be different... at synth time the token is resolved no? so you get a Fn::Join:

aws-cdk/packages/@aws-cdk/aws-cloudfront/test/function.test.ts

Lines 48 to 58 in 94f81c4

    
           Name: { 
        
             'Fn::Join': [ 
        
               '', 
        
               [ 
        
                 { 
        
                   Ref: 'AWS::Region', 
        
                 }, 
        
                 'StackCF2CE3F783F', 
        
               ], 
        
             ], 
        
           },

If you snapshot it, it should always return the same Name?

eladb · 2021-07-15T07:58:47Z

I think the problem is not the sequence number but actually the length of the unresolved token which is truncated (but I am not 100% sure). This requires taking a closer look.

eladb · 2021-07-15T08:02:21Z

@njlynch as you are fixing this, please notice that there seems to be an issue with the AWS::CloudFront::Function resource which causes an update failure if the function name is changed:

Resource handler returned message: "Resource of type 'AWS::CloudFront::Function' with identifier 'us-west-2-c84c29a89f49a9c52cb7670f010af5cc67269f8077' was not found." (RequestToken: dc479a93-2786-8270-92a1-81e3e808eb91, HandlerErrorCode: NotFound)

This is not very surprising since the physical name is explicitly specified. CFN will send an UPDATE operation with the new physical name and the resource provider won't be able to find it (because it should actually delete the old resource and create a new one instead of attempting to update).

A reasonable work around is to find the logical ID of the function to the function name itself so that when the function name changes, a new logical ID will be allocated and the resource will effectively be replaced.

See cdklabs/construct-hub#171

Explicitly set the CloudFront function name so snapshot is stable (see aws/aws-cdk#15523). This also requires updating the logical ID of the AWS::CloudFront::Function resource because it seems like there's a bug in the resource provider that won't allow changing the function name. So changing the logical ID would effectively replace the resource. Re-enable the snapshot test.

madeline-k · 2021-07-16T22:48:39Z

@njlynch Is on vacation until July 22 and I am triaging his issues in the meantime. It looks like this should be a p2 since customers have a workaround to provide an explicit name. Please let me know if anyone disagrees! I will make sure to raise this to Nick as soon as he is back.

eladb · 2021-07-18T08:03:17Z

@madeline-k I don't believe I would tag it as p2 as basically the entire cloudfront.Function feature is broken in this situation. I would tag it as a p1.

Also, please add the workaround to the issue description so people don't have to search for it.

Here is what we did in construct-hub (source).

KTamas · 2021-08-16T15:48:12Z

Tracking this, we got bitten by this as well. Using the workaround for now.

There's an upstream bug in CDK that results in unstable generation of CloudFront function names: aws/aws-cdk#15523

kiernan · 2022-05-16T08:16:37Z

I think the problem is not the sequence number but actually the length of the unresolved token which is truncated (but I am not 100% sure).

This sounds like the behaviour I've just seen.

I had deployed a stack containing a cloudfront function, then went to deploy it again and got an error that it couldn't find a function with the expected ID:

3:58:23 pm | UPDATE_FAILED        | AWS::CloudFront::Function                       | CfnFunctionD7182995
Resource handler returned message: "Resource of type 'AWS::CloudFront::Function' with identifier 'ap-southeast-2kiernanSuSheetWebStackCfnFunction6F1B71FB' was not fo
und."

The ID it's trying to find is almost correct, but has one character missing in the middle compared with the actual ID of the created function.

I hadn't actually made any changes to the anything in the stack containing the cloudfront function, diff shows just the ID changing:

cdk diff kiernan-...omitted/WebStack
Resources
[~] AWS::CloudFront::Function WebStack/CfnFunction CfnFunctionD7182995
 ├─ [~] FunctionConfig
 │   └─ [~] .Comment:
 │       └─ [~] .Fn::Join:
 │           └─ @@ -4,6 +4,6 @@
 │              [ ]     {
 │              [ ]       "Ref": "AWS::Region"
 │              [ ]     },
 │              [-]     "kiernanSupSheetWebStackCfnFunction6F1B71FB"
 │              [+]     "kiernanSuSheetWebStackCfnFunction6F1B71FB"
 │              [ ]   ]
 │              [ ] ]
 └─ [~] Name
     └─ [~] .Fn::Join:
         └─ @@ -4,6 +4,6 @@
            [ ]     {
            [ ]       "Ref": "AWS::Region"
            [ ]     },
            [-]     "kiernanSupSheetWebStackCfnFunction6F1B71FB"
            [+]     "kiernanSuSheetWebStackCfnFunction6F1B71FB"
            [ ]   ]
            [ ] ]

- The bug that a CloudFront function name fluctuated over deployment to deployment is worked around. There is a bug in CDK that it may generate different function names at different deployments. Please see the following issue for more details, - aws/aws-cdk#15523 As suggested in the above issue, I decided to give a fixed name to my CloudFront function. Function names never conflict between development and production stacks because `Node.addr` that is different between them is appended. issue codemonger-io#2

SachinShekhar · 2022-08-10T15:45:11Z

Any update on this? Sometimes my deployment succeeds; sometimes it doesn’t.

joyfulelement · 2023-10-06T14:36:09Z

I think the problem is not the sequence number but actually the length of the unresolved token which is truncated (but I am not 100% sure).

This sounds like the behaviour I've just seen.

I had deployed a stack containing a cloudfront function, then went to deploy it again and got an error that it couldn't find a function with the expected ID:
3:58:23 pm | UPDATE_FAILED        | AWS::CloudFront::Function                       | CfnFunctionD7182995
Resource handler returned message: "Resource of type 'AWS::CloudFront::Function' with identifier 'ap-southeast-2kiernanSuSheetWebStackCfnFunction6F1B71FB' was not fo
und."
The ID it's trying to find is almost correct, but has one character missing in the middle compared with the actual ID of the created function.

I hadn't actually made any changes to the anything in the stack containing the cloudfront function, diff shows just the ID changing:

Encountering the exact same issue which causes the same stack to be re-deployed unexpectedly.

Here is one example with no change of code, but still causing the diff when running cdk diff.

Was using "aws-cdk": "2.99.1"

Resources
[~] AWS::CloudFront::Function ViewerRequestFunction ViewerRequestFunction48E73F66 
 ├─ [~] FunctionConfig
 │   └─ [~] .Comment:
 │       └─ [~] .Fn::Join:
 │           └─ @@ -4,6 +4,6 @@
 │              [ ]     {
 │              [ ]       "Ref": "AWS::Region"
 │              [ ]     },
 │              [-]     "webappriskntxViewerRequestFunction6E8AC013"
 │              [+]     "webapprisntxViewerRequestFunction6E8AC013"
 │              [ ]   ]
 │              [ ] ]
 └─ [~] Name
     └─ [~] .Fn::Join:
         └─ @@ -4,6 +4,6 @@
            [ ]     {
            [ ]       "Ref": "AWS::Region"
            [ ]     },
            [-]     "webappriskntxViewerRequestFunction6E8AC013"
            [+]     "webapprisntxViewerRequestFunction6E8AC013"
            [ ]   ]
            [ ] ]
[~] AWS::CloudFront::Function Function Function76856677 
 ├─ [~] FunctionConfig
 │   └─ [~] .Comment:
 │       └─ [~] .Fn::Join:
 │           └─ @@ -4,6 +4,6 @@
 │              [ ]     {
 │              [ ]       "Ref": "AWS::Region"
 │              [ ]     },
 │              [-]     "webapprisk4proddeploymentxFunction7C5F687C"
 │              [+]     "webappris4proddeploymentxFunction7C5F687C"
 │              [ ]   ]
 │              [ ] ]
 └─ [~] Name
     └─ [~] .Fn::Join:
         └─ @@ -4,6 +4,6 @@
            [ ]     {
            [ ]       "Ref": "AWS::Region"
            [ ]     },
            [-]     "webapprisk4proddeploymentxFunction7C5F687C"
            [+]     "webappris4proddeploymentxFunction7C5F687C"
            [ ]   ]
            [ ] ]
[~] Custom::CDKBucketDeployment DeployS3BucketContentWithCloudFrontInvalidation/CustomResource DeployS3BucketContentWithCloudFrontInvalidationCustomResource101552DD 
 └─ [~] SourceObjectKeys
     └─ @@ -1,3 +1,3 @@
        [ ] [
        [-]   "da1[22](https://adc.github.trendmicro.com/Cloud-ASRM/web-app-risk-explorer/actions/runs/2137227/job/6035773#step:21:23)bd1f16[28](https://adc.github.trendmicro.com/Cloud-ASRM/web-app-risk-explorer/actions/runs/2137227/job/6035773#step:21:29)bbd4164cb84bdcc0457d066c1c83bb28feef9034f9114a5d995.zip"
        [+]   "5aec016f2bc03e9f75f88e434ef2e747e5d47aff17a9d0465eee0[30](https://adc.github.trendmicro.com/Cloud-ASRM/web-app-risk-explorer/actions/runs/2137227/job/6035773#step:21:31)5bb[36](https://adc.github.trendmicro.com/Cloud-ASRM/web-app-risk-explorer/actions/runs/2137227/job/6035773#step:21:37)9eb6.zip"
        [ ] ]


✨  Number of stacks with differences: 1

kiernan · 2023-10-30T09:32:59Z

Here's a CDK Aspect we've used to apply this work-around to functions created within 3rd party constructs, where we can't control the functionName property directly.

import { IAspect } from "aws-cdk-lib";
import { CfnFunction } from "aws-cdk-lib/aws-cloudfront";
import { IConstruct } from "constructs";

/**
 * Work-around a CDK bug which is causing CloudFront Functions to
 * have their Logical ID changed unnecessarily each deployment:
 * https://github.com/aws/aws-cdk/issues/15523
 *
 * Usage example:
 * cdk.Aspects.of(app).add(new RenameCloudFrontFunctionAspect());
 */
export class RenameCloudFrontFunctionAspect implements IAspect {
  visit(node: IConstruct): void {
    if (node instanceof CfnFunction) {
      const name = `CloudFrontFunction${node.node.addr}`;
      node.name = name;
      node.overrideLogicalId(node.name);
    }
  }
}

If you had a lot of functions, you could also look at getting a better prefix to use from the ID of the construct (or its parent, if any were intentionally given the special name, 'Default').
That is just so they are more recognisable when viewing in the console, or in the generated CloudFormation output.

### Issue # (if applicable) Closes #20017 as well as #15523 and #28629 ### Reason for this change Due to the way function names are generated using token strings with either single- or double-digit numbers, longer function names can be truncated differently, leading to inconsistency in generated CloudFormation templates. ### Description of changes To ensure backwards compatibility, if names are longer than 64 characters and use region tokens, if the token uses a single-digit region number, it takes the first **31** characters + the last 32 characters; if the token uses a double-digit region number or otherwise, it takes the first **32** characters + the last 32 characters. This ensures it will always take the same first chunk of the actual function's name. ### Description of how you validated changes A new unit test was added to verify the consistency of function names in the template. ### Checklist - [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md) ---- *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

github-actions · 2024-06-12T13:31:52Z

⚠️COMMENT VISIBILITY WARNING⚠️

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If you need more assistance, please either tag a team member or open a new issue that references this one.
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### Issue # (if applicable) Closes aws#20017 as well as aws#15523 and aws#28629 ### Reason for this change Due to the way function names are generated using token strings with either single- or double-digit numbers, longer function names can be truncated differently, leading to inconsistency in generated CloudFormation templates. ### Description of changes To ensure backwards compatibility, if names are longer than 64 characters and use region tokens, if the token uses a single-digit region number, it takes the first **31** characters + the last 32 characters; if the token uses a double-digit region number or otherwise, it takes the first **32** characters + the last 32 characters. This ensures it will always take the same first chunk of the actual function's name. ### Description of how you validated changes A new unit test was added to verify the consistency of function names in the template. ### Checklist - [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md) ---- *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

iliapolo added bug This issue is a bug. needs-triage This issue or PR still needs to be triaged. labels Jul 13, 2021

github-actions bot added the @aws-cdk/aws-cloudfront Related to Amazon CloudFront label Jul 13, 2021

github-actions bot assigned njlynch Jul 13, 2021

iliapolo mentioned this issue Jul 13, 2021

fix: golden snapshot is unstable due to CF function name generation cdklabs/construct-hub#171

Merged

madeline-k added effort/medium Medium work item – several days of effort p2 and removed needs-triage This issue or PR still needs to be triaged. labels Jul 16, 2021

madeline-k added p1 and removed p2 labels Jul 19, 2021

njlynch removed their assignment Jul 23, 2021

njlynch mentioned this issue Aug 13, 2021

(cloudfront): identifier not found #15765

Closed

stekern added a commit to capralifecycle/liflig-cdk that referenced this issue Nov 8, 2021

fix(flaky-test): use stable logical id for CloudFront function

eae3dda

There's an upstream bug in CDK that results in unstable generation of CloudFront function names: aws/aws-cdk#15523

Leo10Gama mentioned this issue May 30, 2024

fix(cloudfront): make long function name deterministic #30392

Merged

1 task

pahud added p2 and removed p1 labels Jun 11, 2024

Leo10Gama closed this as completed Jun 12, 2024

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[Snyk] Upgrade: , aws-cdk NOUIY/aws-solutions-constructs#107

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[Snyk] Upgrade: , aws-cdk NOUIY/aws-solutions-constructs#108

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(aws-cloudfront): Unexpected diffs caused by cloudfront.Function #15523

(aws-cloudfront): Unexpected diffs caused by cloudfront.Function #15523

iliapolo commented Jul 13, 2021 •

edited by madeline-k

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jogold commented Jul 14, 2021

eladb commented Jul 15, 2021

eladb commented Jul 15, 2021

madeline-k commented Jul 16, 2021

eladb commented Jul 18, 2021

KTamas commented Aug 16, 2021

kiernan commented May 16, 2022

SachinShekhar commented Aug 10, 2022

joyfulelement commented Oct 6, 2023

kiernan commented Oct 30, 2023

github-actions bot commented Jun 12, 2024

(aws-cloudfront): Unexpected diffs caused by cloudfront.Function #15523

(aws-cloudfront): Unexpected diffs caused by cloudfront.Function #15523

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iliapolo commented Jul 13, 2021 • edited by madeline-k Loading

Reproduction Steps

What did you expect to happen?

What actually happened?

Environment

Other

Workaround

hoegertn commented Jul 13, 2021

eladb commented Jul 13, 2021 • edited Loading

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eladb commented Jul 13, 2021

hoegertn commented Jul 13, 2021

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eladb commented Jul 15, 2021

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madeline-k commented Jul 16, 2021

eladb commented Jul 18, 2021

KTamas commented Aug 16, 2021

kiernan commented May 16, 2022

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kiernan commented Oct 30, 2023

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iliapolo commented Jul 13, 2021 •

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