Add lifecyle ignore changes on AZs to aws_rds_cluster resource

[AkramDhiabi]

Is your request related to a new offering from AWS?

Is this functionality available in the AWS provider for Terraform? See CHANGELOG.md, too.

• Yes ✅: aws version : 5.42

Is your request related to a problem? Please describe.

RDS automatically assigns 3 AZs if less than 3 AZs are configured, which will show as a difference requiring resource recreation next Terraform apply

Describe the solution you'd like.

I'm requesting an update to our RDS cluster Aurora module to include a lifecycle block with the ignore_changes configuration for the availability_zones argument. This change is necessary to address the following issue:

• When specifying fewer than three availability zones (AZs), RDS automatically assigns three AZs, which Terraform interprets as a configuration change requiring resource recreation during subsequent plans.
• Resource recreation leads to downtime, which we want to avoid.

By adding the lifecycle block to ignore changes in availability_zones, we can maintain consistency in our configuration and avoid unnecessary resource recreation and downtime.

Describe alternatives you've considered.

Here is the code snippet to add here:

lifecycle {
  ignore_changes = [
    "availability_zones"
  ]
}

Additional context

N/A

[bryantbiggs]

I don't see a valid reason to ignore this - the API is clear in that its a replace operation when the value has changed https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-rds-dbcluster.html#cfn-rds-dbcluster-availabilityzones

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