feat(autoscaling): instance maintenance policy for AutoScalingGroup

[go-to-k]

This PR supports for configuring AutoScalingGroup's instance maintenance policy.

• https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-autoscaling-autoscalinggroup-instancemaintenancepolicy.html
• https://docs.aws.amazon.com/autoscaling/ec2/userguide/ec2-auto-scaling-instance-maintenance-policy.html
• https://docs.aws.amazon.com/autoscaling/ec2/userguide/instance-maintenance-policy-overview-and-considerations.html

Closes #28042.

---

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[lpizzinidev]

Thanks 👍
I added some suggestions for improvements, feel free to comment.

[go-to-k]

@lpizzinidev

Thanks for your review. I fixed them!

[go-to-k]

@lpizzinidev

I changed the properties to flat and optional! Please check them.

[lpizzinidev]

Thanks 👍
Just some minor adjustments and it will be good to go for me.

[go-to-k]

@lpizzinidev

I changed. Please look at this comment.

[lpizzinidev]

Thanks 👍

[kaizencc]

Thanks @go-to-k. Some minor comments, but great start!

[kaizencc]

Suggested change

	The instance maintenance policy allows you to configure an instance maintenance policy for
	You can configure an instance maintenance policy for

[go-to-k]

I changed.

[kaizencc]

I'm not necessarily against this, but what was the reasoning against just minHealthPercentage and maxHealthPercentage? I think i prefer that unless it would be confusing if minimum health could point to other things besides maintenance policy.

[go-to-k]

Yes, I was not sure at first, but I think I will do that.

[go-to-k]

Changed to minHealthyPercentage and maxHealthyPercentage to match CloudFormation (with Health'y').

[kaizencc]

If possible, I think we should just set the default to -1. If I am reading the docs correctly, this is equivalent to undefined in CloudFormation. The only issue I see is if CloudFormation somehow fails if you set the value to -1 and there wasn't any previous value to clear. If that happens, then lets go down this path. If not, we can treat -1 and undefined equivalently in CDK.

[go-to-k]

When I tried to run CloudFormation with -1 from the beginning, I got the following error in CFn. In other words, it seems that -1 and undefined must be distinguished.

MinHealthyPercentage must be between 0 and 100 (inclusive).

[kaizencc]

:(

[kaizencc]

Suggested change

	if (maxHealthPercentage === -1 && minHealthPercentage === -1) {
	return {
	maxHealthyPercentage: maxHealthPercentage,
	minHealthyPercentage: minHealthPercentage,
	};
	}
	if (minHealthPercentage === -1 || maxHealthPercentage === -1) {
	throw new Error(`Both maintenancePolicyMinHealthPercentage and maintenancePolicyMaxHealthPercentage must be -1 to clear the previously set value, got maintenancePolicyMinHealthPercentage: ${minHealthPercentage} and maintenancePolicyMaxHealthPercentage: ${maxHealthPercentage}`);
	}
	if (minHealthPercentage === -1 || maxHealthPercentage === -1 && minHealthPercentage !== maxHealthPercentage) {
	throw new Error(`Both maintenancePolicyMinHealthPercentage and maintenancePolicyMaxHealthPercentage must be -1 to clear the previously set value, got maintenancePolicyMinHealthPercentage: ${minHealthPercentage} and maintenancePolicyMaxHealthPercentage: ${maxHealthPercentage}`);
	}

This would be equivalent and remove an additional if condition, but isn't a huge deal.

[go-to-k]

No, in the case for the code and both maxHealthPercentage and minHealthPercentage is -1, the next branch causes an error.

    if (maxHealthPercentage < 100 || maxHealthPercentage > 200) {
      throw new Error(`maxHealthPercentage must be between 100 and 200, or -1 to clear the previously set value, got ${maxHealthPercentage}`);
    }
    if (minHealthPercentage < 0 || minHealthPercentage > 100) {
      throw new Error(`minHealthPercentage must be between 0 and 100, or -1 to clear the previously set value, got ${minHealthPercentage}`);
    }

So, if both are -1, we need to return them as soon as possible.

[go-to-k]

Or, the following code would work. I will go with this!

    if ((minHealthPercentage === -1 || maxHealthPercentage === -1) && minHealthPercentage !== maxHealthPercentage) {
      throw new Error(`Both minHealthPercentage and maxHealthPercentage must be -1 to clear the previously set value, got minHealthPercentage: ${minHealthPercentage} and maxHealthPercentage: ${maxHealthPercentage}`);
    }
    if (maxHealthPercentage !== -1 && (maxHealthPercentage < 100 || maxHealthPercentage > 200)) {
      throw new Error(`maxHealthPercentage must be between 100 and 200, or -1 to clear the previously set value, got ${maxHealthPercentage}`);
    }
    if (minHealthPercentage !== -1 && (minHealthPercentage < 0 || minHealthPercentage > 100)) {
      throw new Error(`minHealthPercentage must be between 0 and 100, or -1 to clear the previously set value, got ${minHealthPercentage}`);
    }

[go-to-k]

I changed.

[kaizencc]

We can store all errors we get in an array and throw them all at the same time, so the user will know all the issues present.

[go-to-k]

Hmmm, is that necessary?

I think the information given to the user would be more complex, and type inference would not work and branching would become more complicated.

(Because of the eslint error, in numerical comparisons, minHealthyPercentage !== undefined and maxHealthyPercentage !== undefined must be added to the numerical comparison.)

    const errors: string[] = [];

    if (minHealthyPercentage === undefined && maxHealthyPercentage === undefined) return;
    if (minHealthyPercentage === undefined || maxHealthyPercentage === undefined) {
      errors.push(`Both or neither of minHealthyPercentage and maxHealthyPercentage must be specified, got minHealthyPercentage: ${minHealthyPercentage} and maxHealthyPercentage: ${maxHealthyPercentage}`);
    }
    if ((minHealthyPercentage === -1 || maxHealthyPercentage === -1) && minHealthyPercentage !== maxHealthyPercentage) {
      errors.push(`Both minHealthyPercentage and maxHealthyPercentage must be -1 to clear the previously set value, got minHealthyPercentage: ${minHealthyPercentage} and maxHealthyPercentage: ${maxHealthyPercentage}`);
    }
    if (minHealthyPercentage !== -1 && minHealthyPercentage !== undefined && (minHealthyPercentage < 0 || minHealthyPercentage > 100)) {
      errors.push(`minHealthyPercentage must be between 0 and 100, or -1 to clear the previously set value, got ${minHealthyPercentage}`);
    }
    if (maxHealthyPercentage !== -1 && maxHealthyPercentage !== undefined && (maxHealthyPercentage < 0 || maxHealthyPercentage > 100)) {
      errors.push(`maxHealthyPercentage must be between 100 and 200, or -1 to clear the previously set value, got ${maxHealthyPercentage}`);
    }
    if (maxHealthyPercentage !== undefined && minHealthyPercentage !== undefined && maxHealthyPercentage - minHealthyPercentage > 100) {
      errors.push(`The difference between minHealthyPercentage and maxHealthyPercentage cannot be greater than 100, got ${maxHealthyPercentage - minHealthyPercentage}`);
    }

    if (errors.length > 0) {
      throw new Error(errors.join('\n'));
    }

    return {
      minHealthyPercentage,
      maxHealthyPercentage,
    };

Pull request has been modified.

[go-to-k]

@kaizencc

Thanks for your review!

I fixed and commented back. I would especially appreciate it if you would read the following comment.

#28092 (comment)

[kaizencc]

I think the -1 thing is kind of dumb but I can't think of a reasonable way of doing it in cdk-land besides just passing on that user-experience to the user. Oh well. Everything else looks good -- my comments on the errors were just nits anyway. Thanks again.

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