(aws-lambda): Switching scaling option doesn't update the Provisioned Concurrency

[garysassano]

Describe the bug

Starting point:

const scalableFunction = new NodejsFunction(this, "ScalableFunction", {
  functionName: "scalable-function",
  entry: join(__dirname, "..", "functions", "scalable", "index.ts"),
  runtime: Runtime.NODEJS_20_X,
  architecture: Architecture.ARM_64,
  memorySize: 1024,
  timeout: Duration.minutes(5),
  loggingFormat: LoggingFormat.JSON,
});

const scalableFunctionAlias = new Alias(this, "ScalableFunctionAlias", {
  aliasName: "live",
  version: scalableFunction.currentVersion,
});

scalableFunctionAlias
  .addAutoScaling({
    minCapacity: 1,
    maxCapacity: 10,
  })
  .scaleOnSchedule("ScaleUpInMorning", {
    schedule: Schedule.cron({ hour: "3", minute: "30" }),
    minCapacity: 5,
  });

I deploy the code, wait for the scheduled time and check that the Provisioned Concurrency correctly changed from 1 to 5 in Lambda AWS Console.

Then I update the code as follows:

scalableFunctionAlias
  .addAutoScaling({
    minCapacity: 1,
    maxCapacity: 10,
  })
  .scaleOnUtilization({
    utilizationTarget: 0.7,
  });

I deploy it and go check again in Lambda AWS Console:

The Provisioned Concurrency is still 5, it didn't get updated to the default minCapacity.

Expected Behavior

see above

Current Behavior

see above

Reproduction Steps

see above

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.145.0

Framework Version

No response

Node.js Version

20.13.1

OS

Ubuntu 22.04.3 LTS

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

I think it makes sense here.

minCapacity is the minimal capacity to scale to. It doesn't mean it has to scale to that value on stack update.

Per CFN doc[1]:

The minimum value that you plan to scale in to. When a scaling policy is in effect, Application Auto Scaling can scale in (contract) as needed to the minimum capacity limit in response to changing demand.

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