(aws_stepfunctions_tasks): Lambda Functions deployed with LambdaInvoke won't generate Cloudwatch metrics

[quentinbarbault]

Describe the bug

Hello,

I think I've found an issue with CDK and the way it adds Lambda function to the JSON definition with LambdaInvoke. This disables the possibility to get [Lambda Function Metrics] in Cloudwatch.

Let me explain.

We are using CDK to create our State Machine. To add Lambda Functions to our State Machine, we use LambdaInvoke, as intended. https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_stepfunctions_tasks.LambdaInvoke.html

This generates a definition, with States juste like this :

"LambdaState1": {
    "Next": "LambdaState2",
    "Type": "Task",
    "Resource": "arn:aws:states:::lambda:invoke",
    "Parameters": {
        "FunctionName": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
    }
},

Please note that this definition has :

• Resource as "arn:aws:states:::lambda:invoke"
• Parameters.FunctionName as our Lambda Arn

Our state machine is running fine but this definition doesn't generate any metrics (such as "LambdaFunctionsStarted", "LambdaFunctionsSucceeded" and so on) for our deployed lambda functions.

As a matter of fact, the State Machine does not consider this state (here LambdaState1) as a LambdaFunction, but as a simple Task. Which, I presume, is the issue here.

When playing with this, I've found that this following definition does work.

"LambdaState1": {
    "Next": "LambdaState2",
    "Type": "Task",
    "Resource": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
},

The state is considered a LambdaFunction, not a Task, from the state machine's point of view. And, more importantly, metrics from this Lambda are indeed created.

But I can't seem to figure out how to force LambdaInvoke to generate something like this. With the ARN as a ressource.

So I suspect something is not quite right here.

Expected Behavior

I would expect LambdaInvoke to add lambda functions as LambdaFunction, and not as Task.

Even if the documentation clealy states : "Invoke a Lambda function as a Task.". If so, how can I force CDK to treat my Lambda as a LambdaFunction ? Is there any property available to do that ?

Current Behavior

Adding a lambda function to a state machine like this:

const myLambdaState = new LambdaInvoke(
            this,
            "my-lambda-state",
            {
                lambdaFunction: new NodeJsFunction(...),
                retryOnServiceExceptions: false,
            }
        );

Generates the following definition :

"myLambdaState": {
    "End": "true",
    "Type": "Task",
    "Resource": "arn:aws:states:::lambda:invoke",
    "Parameters": {
        "FunctionName": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
    }
},

Instead of:

"myLambdaState": {
    "End": "true",
    "Type": "Task",
    "Resource": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
},

So the lambda is not considered a LambdaFunction, but a Task, for the StateMachine, hence not generating any Lambda specific metrics.

Reproduction Steps

Any lambda function deployed with LambdaInvoke will have the following definition:

"myLambdaState": {
    "End": "true",
    "Type": "Task",
    "Resource": "arn:aws:states:::lambda:invoke",
    "Parameters": {
        "FunctionName": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
    }
},

Any new execution will work but you'll find that no metrics in [Lambda Function Metrics] is available.

Possible Solution

When using LambdaInvoke, CDK could create the following definition instead:

"myLambdaState": {
    "End": "true",
    "Type": "Task",
    "Resource": "arn:aws:lambda:eu-west-3:ACCOUNT:function:Lambda1ARN"
},

Additional Information/Context

No response

CDK CLI Version

2.63.1

Framework Version

No response

Node.js Version

16

OS

Windows

Language

Typescript

Language Version

No response

Other information

No response

[pahud]

You are right. LambdaInvoke is actually a task that extends sfn.TaskStateBase and execute the lambda:Invoke API call.

And according to the doc, we can pass the lambda func arn in the Resource attribute:

Alternatively, you can invoke a Lambda function by specifying a function ARN directly in the "Resource" field. When you invoke a Lambda function in this way, you can't specify .waitForTaskToken, and the task result contains only the function output.

{  
   "StartAt":"CallFunction",
   "States":{  
      "CallFunction": {  
         "Type":"Task",
         "Resource":"arn:aws:lambda:us-east-1:123456789012:function:HelloFunction",
         "End": true
      }
   }
}     

It seems this alternative has some limitations though.

I am making this a p2 feature request. Any inputs on this are more than welcome here.