CDK Watch not working with NodejsFunction

[joshiatxcira]

I currently use NodejsFunction to create/update lambda resources. My lambda is written in typescript.
Key NodejsFunctionProps provided are "entry" and "minify=true bundling".

I was looking to hotswap the lambda modifications after each save using cdk watch.
What I have noticed is, each time I save my lambda handler, a new asset is created. As a result, cdk watch command thinks it has newer asset to deploy and it runs full deployment.
Please let me know if any options in NodejsFunction would help it work with "cdk watch".
Thanks.

[skinny85]

Can you show the relevant part of your CDK code, and the output of cdk diff when you make the change to your code?

[joshiatxcira]

Thank you for your response. Below is what "cdk diff" gave me after saving my lambda handler.
Sorry for the bad formatting earlier.

$ cdk diff MyStack

Bundling asset MyStack/Lambda_MY_LAMBDALambda/Code/Stage...
 cdk\cdk.out\bundling-temp-018bd6e5146cf42c67a631126c459ca3544b504118bfc91c399b2480b4abeaef\index.js  719b 
Done in 8ms
Stack MyStack
Resources
[ ~ ] AWS::AppSync::ApiKey MyAppSyncAPI/MyAppSyncAPIAccessKeyApiKey 
 MyAppSyncAPIMyAppSyncAPIAccessKeyKey5753F94E 
 └─ [ ~ ] Expires
     ├─ [-] 1658674237
     └─ [+] 1658776804
[ ~ ] AWS::Lambda::Function Lambda_MY_LAMBDALambda LambdaMY_LAMBDALambda570470AE
 ├─ [ ~] Code
 │   └─ [ ~] .S3Key:
 │       ├─ [-] 8af213236d80af46aba469396658496f6a141f65221ddf5915a7b15156ea3f41.zip
 │       └─ [+] eb22c10fdc03adde048df6dbee436f9c9a461517254410db93d6ccf9f1e542bb.zip
 └─ [ ~] Metadata
     └─ [ ~] .aws:asset:path:
         ├─ [-] asset.8af213236d80af46aba469396658496f6a141f65221ddf5915a7b15156ea3f41
         └─ [+] asset.eb22c10fdc03adde048df6dbee436f9c9a461517254410db93d6ccf9f1e542bb

Below are the relevant parts of the CDK code. My objection, I would like to hotswap my lambda handler changes when I run "cdk watch" command.

/* Lambda handler */
export const handler = async (event: any) => {

  // README - this is the piece of code that I need to hotswap during "cdk watch"
  
  // business logic to create object goes here
  return object;
}

/* Lambda creation code using NodejsFunction  */
export const MyObjectLambda = (scope: any) =>
  createLambda(scope, {
    functionName: MY_LAMBDA,
    entry: join(__dirname, 'MY_LAMBDA_DIR/index.ts'),
    timeout: Duration.seconds(60),
    tracing: Tracing.ACTIVE
  })

const createLambda = (scope: any, config: NodejsFunctionProps) => {

  const functionName = config.functionName
  const ResourcePrefix = `Lambda_${functionName}`

  const props: NodejsFunctionProps = {
    handler: 'handler',
    bundling: {
      minify: true
    },
    timeout: aws_lambda.Duration.seconds(15),
    tracing: Tracing.ACTIVE,
    architecture: Architecture.ARM_64,
    memorySize: 512,
    ...config
  };

  const lambda = new NodejsFunction(scope, ResourcePrefix, props);

  lambda.addEnvironment('branch_name', branch_name)

  return lambda
}

/* Stack to create/update lambda  */
export class MyStack extends Stack {

  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);

	configureAppSyncAPI();
	
    const { lambdas } = allApplicationLambdas;

    // Generate Lambdas -> calls MyObjectLambda function above
    Object.values(lambdas).forEach((configLambda: any) => configLambda(this))
  }
  
  configureAppSyncAPI() {
    const appsyncName = 'MyAppSyncAPI'
  
    new GraphqlApi(this, appsyncName, {
      name: appsyncName,
      logConfig: {
        fieldLogLevel: FieldLogLevel.ERROR
      },
      xrayEnabled: true,
      authorizationConfig: {
        defaultAuthorization: {
          authorizationType: AuthorizationType.API_KEY,
          apiKeyConfig: {
            description: 'MyAppSyncAPI Access key',
            expires: Expiration.after(Duration.days(90)),
            name: 'MyAppSyncAPIAccessKey'
          }
        }
      }
    })
}

[skinny85]

So the problem is this line in the diff:

[ ~ ] AWS::AppSync::ApiKey MyAppSyncAPI/MyAppSyncAPIAccessKeyApiKey 
 MyAppSyncAPIMyAppSyncAPIAccessKeyKey5753F94E 
 └─ [ ~ ] Expires
     ├─ [-] 1658674237
     └─ [+] 1658776804

Something changes about AWS::AppSync::ApiKey, and so hotswapping cannot proceed (it doesn't know how to handle changes to the Expires property of AWS::AppSync::ApiKey), and falls back to doing a full deployment.

Do you know where does that change in the Expires property come from, if you're only changing the code of your Function?

[joshiatxcira]

You are correct - the key comes from AppSync API Key configuration in the stack. I had it as

Expiration.after(Duration.days(90))

Above meant, CDK was extending the key by 90 days on each pass. I changed the key expiry logic and was able to successfully see "cdk watch" in action. Here is my updated expiry logic

Expiration.atDate(new Date('XXXX-XX-XXT00:00:00'))

@skinny85 Thank you for taking time to look into my problem.

[github-actions[bot]]

Hello! Reopening this discussion to make it searchable.