feat(lambda): autoscaling for lambda aliases

[kaizencc]

Add support for autoscaling provisioned concurrency on lambda (closes #6400).
To set autoscaling on a function alias use the addAutoScaling() method:

const alias = new lambda.Alias(stack, 'Alias', {
  aliasName: 'prod',
  version,
});

// Create AutoScaling Target
const as = alias.addAutoScaling({ maxCapacity: 50 })

// Configure target tracking
as.scaleOnUtilization({ utilizationTarget: 0.5 });

// or configure schedule scaling
as.scaleOnSchedule('ScaleUpInTheMorning', {
  schedule: appscaling.Schedule.cron({ hour: '8', minute: '0'}),
  minCapacity: 20,
});

It's possible to set PC on a function version, why didn't you add this option?
Following guidance from @iph:

The resource: AWS::Lambda::Version today is brittle and a sharp edge for many customers in how it behaves. We have a small flag in our cfn docs which needs to be bolder, in red, and said twice for ProvisionedConcurrencyConfig.
Versions do not support updates, so if you try to set a PC value on a version that already exists -- your cfn rolls back permanently. If you try to only update a PC configuration on a version cfn rolls back permanently. If you replace a version by changing the logical id, but set your version to retain-- your previous PC Configuration values are stranded, costing the customer. Overall, the Lambda team went back and forth whether we wanted to keep this functionality at all in cloudformation and decided "some customers may find a way to use it, and we should not inhibit them -- but direct everyone else to Alias-PC".
I would like us to retain that same philosophy in the L2 by not exposing the sharp edge to customers --they can still use it in the L1 if they so desire.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

Pull request has been modified.

[nija-at]

Looks mostly good to me. A few small comments below.

[nija-at]

Would this be a better user experience if we change this to a getter autoscaling that (instantiates, if not already, and) returns scalableAlias?

[NetaNir]

I think we might want to keep the same pattern as we have in all other L2 which implements autoscaling (ecs, ddb, ec2)

[nija-at]

I agree with returning IScalableFunctionAttribute in the addAutoScaling() method.

My question is if this should be -

export class ScalableFunctionAttribute extends appscaling.BaseScalableAttribute implements IScalableFunctionAttribute {

Keeps the type expectations in the correct place and any mismatches will be reported at the correct locations by the compiler.

[NetaNir]

I see, you are right, I have change it!

[nija-at]

Is there a nice default we can configure here? 0.9 maybe?

[nija-at]

Ping. This comment is not addressed.

[NetaNir]

There is no good default here, every use case will have a different "best" target value, depending on the customer provision concurrency value, target cost and other usage pattern, requiring the value here makes the customer fully aware of the cost associate with the value.

[nija-at]

Ping. This comment is not addressed.

[nija-at]

I agree with returning IScalableFunctionAttribute in the addAutoScaling() method.

My question is if this should be -

export class ScalableFunctionAttribute extends appscaling.BaseScalableAttribute implements IScalableFunctionAttribute {

Keeps the type expectations in the correct place and any mismatches will be reported at the correct locations by the compiler.

[nija-at]

Same here. Drop this in favour of the documentation on utilizationTarget property.

[NetaNir]

I have removed it in all places you commented on, since I rename the file it does not show it.

[nija-at]

Suggested change

	new cdk.CfnOutput(this, 'Output', {
	new cdk.CfnOutput(this, 'FunctionName', {

[nija-at]

Suggested change

	throw new Error('Utilization Target should be between 0.1 and 0.9.');
	throw new Error(`Utilization Target should be between 0.1 and 0.9. Found ${options.utilizationTarget}`);

[aws-cdk-automation]

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[NetaNir]

@Mergifyio refresh