[aws-lambda] lambda.Function.fromFunctionArn is not returning the role, role is undefined

[I2olanD]

lambda.Function.fromFunctionArn is not returning the role

Reproduction Steps

const lambdaProperties = {...};

const myFn = lambda.Function.fromFunctionArn(....);

lambdaProperties.onFailure = new destinations.LambdaDestination(myFn);

new lambda.Function(scope, lambdaName, lambdaProperties);

What did you expect to happen?

fromFunctionArn() returns all information needed to add a destination.

What actually happened?

It throws following error: No child with id:....

Environment

• CLI Version: latest
• Framework Version: latest
• Node.js Version: 10.19.0
• OS :
• Language (Version): [TypeScript (3.7.2)]

Other

It seems like, that the role information is getting lost after calling fromFunctionArn().

static fromFunctionArn(scope, id, functionArn) {
  return Function.fromFunctionAttributes(scope, id, { functionArn });
}

static fromFunctionAttributes(scope, id, attrs) {
  const functionArn = attrs.functionArn;
  const functionName = extractNameFromArn(attrs.functionArn);
  const role = attrs.role;
  console.log(role); // undefined since attrs only contains functionArn
  ......
}

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

Line 362 in ad9a705

return Function.fromFunctionAttributes(scope, id, { functionArn });

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This is 🐛 Bug Report

[nija-at]

Hello @I2olanD -

Currently, the CDK cannot determine the IAM role you are using based on just the function ARN.

You will need to use fromFunctionAttributes() for your use case, and explicitly specify the IAM role. Most likely the IAM role is also defined outside of the CDK app, so it will also have to be imported. Your code will look something like -

const myFn = lambda.Function.fromFunctionArn(this, 'function', {
  functionArn: 'function-arn',
  role: iam.Role.fromRoleArn(this, 'role', 'role-arn'),
});

Let me know if I missed something here.

[alonsnir]

@nija-at

const myFn = lambda.Function.fromFunctionArn(this, 'function', {
  functionArn: 'function-arn',
  role: iam.Role.fromRoleArn(this, 'role', 'role-arn'),
});

How is this possible given the api?

/**
   * Import a lambda function into the CDK using its ARN
   */
  public static fromFunctionArn(scope: Construct, id: string, functionArn: string): IFunction {
    return Function.fromFunctionAttributes(scope, id, { functionArn });
  }