CloudFront.testFunction throws internal error

Question

I’m having a Cloudfront function that is working perfectly, as I expect. I have extended the deployment script to include a test, which was working fine in 2024. I’ve now applied some minor changes to the function, deployed it, and it works again all fine. But the tests are not working anymore, throwing an internal error (with the previous as well as the new version of the function code).

Here’s a version of the code that is simplified, but still generates the error.

```ts
import {CloudFront} from '@aws-sdk/client-cloudfront'

const cloudfront = new CloudFront({
  apiVersion: '2023-05-03',
  region: 'eu-central-1',
})

const Name = 'Bot_detector'

const EventObject = Buffer.from(
  JSON.stringify({
    version: '1.0',
    context: {eventType: 'viewer-request'},
    request: {method: 'GET', uri: '/'},
  })
)

const functionRef = await cloudfront.describeFunction({Name})

await cloudfront.testFunction({
  IfMatch: functionRef.ETag,
  Stage: 'DEVELOPMENT',
  Name,
  EventObject,
})

```

In this test code, the error throws on invocation of `testFunction` as prints the following.

```
/path/to/repository/node_modules/.pnpm/@smithy+smithy-client@3.1.1/node_modules/@smithy/smithy-client/dist-cjs/index.js:839
  const response = new exceptionCtor({
                   ^

CloudFrontServiceException [InternalError]: UnknownError
    at throwDefaultError (/path/to/repository/node_modules/.pnpm/@smithy+smithy-client@3.1.1/node_modules/@smithy/smithy-client/dist-cjs/index.js:839:20)
    at  (/path/to/repository/node_modules/.pnpm/@smithy+smithy-client@3.1.1/node_modules/@smithy/smithy-client/dist-cjs/index.js:848:5)
    at de_CommandError (/path/to/repository/node_modules/.pnpm/@aws-sdk+client-cloudfront@3.592.0/node_modules/@aws-sdk/client-cloudfront/dist-cjs/index.js:6810:14)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at  (/path/to/repository/node_modules/.pnpm/@smithy+middleware-serde@3.0.0/node_modules/@smithy/middleware-serde/dist-cjs/index.js:35:20)
    at  (/path/to/repository/node_modules/.pnpm/@smithy+core@2.2.0/node_modules/@smithy/core/dist-cjs/index.js:165:18)
    at  (/path/to/repository/node_modules/.pnpm/@smithy+middleware-retry@3.0.3/node_modules/@smithy/middleware-retry/dist-cjs/index.js:320:38)
    at  (/path/to/repository/node_modules/.pnpm/@aws-sdk+middleware-logger@3.577.0/node_modules/@aws-sdk/middleware-logger/dist-cjs/index.js:34:22)
    at testFunction (/path/to/repository/cloudfront/deploy.mts:128:26)
    at async Promise.all (index 0) {
  '$fault': 'client',
  '$metadata': {
    httpStatusCode: 500,
    requestId: '1858a535-8df8-4fd3-bf61-865870165bd4',
    extendedRequestId: undefined,
    cfId: undefined,
    attempts: 3,
    totalRetryDelay: 163
  },
  Type: 'Receiver',
  Code: 'InternalError'
}
```

Happens on `@aws-sdk/client-cloudfront` versions 3.592 and 3.777, running on Node 18.13.

Kidd Ip · Answer

It may related to several factors, please try at the following:

1. Validate the Event Object
Ensure that the event object is correctly formatted and adheres to the expected structure for CloudFront functions. The event object must be Base64-encoded binary data and follow the guidelines in the CloudFront documentation:

```
{
  "version": "1.0",
  "context": {
    "eventType": "viewer-request"
  },
  "request": {
    "method": "GET",
    "uri": "/",
    "headers": {
      "host": {
        "value": "example.com"
      }
    }
  }
}
```

Ensure that headers, cookies, and query strings are in lowercase as required.

2. Check the Function's Stage
Verify that the function's stage is set to DEVELOPMENT or LIVE correctly. If the function is unpublished or in an invalid stage, it might cause errors.

3. Update SDK and Dependencies
Ensure that you're using the latest version of the AWS SDK for JavaScript. Sometimes, bugs in older versions can cause unexpected errors:

```
npm update @aws-sdk/client-cloudfront
```

Also, check for compatibility between Node.js version 18.13 and the SDK.

4. Debugging the Function
Use the FunctionExecutionLogs returned by testFunction to identify issues within the function's code. If the logs are empty, it might indicate a problem with how the function is being invoked.

5. Retry Logic
The error metadata indicates multiple retry attempts. Implement exponential backoff in your code to handle transient errors:

```
const retryOptions = {
  maxRetries: 5,
  retryDelayOptions: { base: 200 }
};
const cloudfront = new CloudFront({ region: 'eu-central-1', retryOptions });
```

6. Test with CLI
If the SDK continues to throw errors, test the function using the AWS CLI to isolate the issue:

```
aws cloudfront test-function \
  --name Bot_detector \
  --if-match  \
  --event-object fileb://event.json \
  --stage DEVELOPMENT
```

This can help determine if the issue is with the SDK or the function itself.

Herman · Answer

In my case the problem was that my response object was missing the "statusDescription" field. I suggest generating an event using the UI and copying the JSON into your test.

CloudFront.testFunction throws internal error

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