A method to override configuration and meta arguments within a module

[elliott-weston-cko]

Current Terraform Version

Terraform v0.14.3

Use-cases

Terraform currently only allows the lifecycle meta-argument to be used within the declaration of a resource. It would be really useful if users were able to specify lifecycle blocks in modules that can then be applicable to some/all of the resources within that module.

The main use-case I have is being able to use the ignore_changes to instruct terraform to ignore changes to resources or particular attributes of resources.

Proposal

For example, lets assume I create a terraform module to be used in AWS, and as part of that module I create a dynamodb table. DynamoDB tables (among other resources) have the ability to autoscale, the autoscaling configuration is defined by another resource. Consequently, a lifecycle block must be used to prevent the resource that creates the dynamodb table from modifying the read/write capacity.

In this scenario I currently have to choose to either to support autoscaling or to not support autoscaling, as I cannot pass define a lifecycle block with the ignore_changes argument.
Ideally, I'd like to be able to do something like this:

module "my-module" {
  source = "./my-module/"
  name = "foo-service"

  hash_key = "FooID"
  attributes = [
    {
      name = "FooID"
      type = "S"
    }
  ]
  lifecycle {
    ignore_changes = [
      aws_dynamodb_table.table.read_capacity,
      aws_dynamodb_table.table.write_capacity
    ]
  }
}

Being able to apply lifecycle blocks similarly to the way shown above, would enable me to manage the attributes of this resource outside of this module (whether that's via some automated process, or another resource/module definition), and would allow more people to use this module as it would be usable for a wider range of use-cases.

The documentation states that the lifecycle block can only support literal values, I'm unsure if my proposal would fall under that, as its referring to resources (and possibly attributes) that are created within the module itself 🤔

References

• Partial/Progressive Configuration Changes #4149 (Possibly)

[jleloup]

I am also interested by such feature though it would be to use a prevent_destroy lifecycle directive.

[jaceklabuda]

It will be very useful with AWD RDS module.

module "db" {
  source = "terraform-aws-modules/rds/aws"
  ...
  snapshot_identifier = "..."
  password = "..."
  
  lifecycle {
    ignore_changes = [
      snapshot_identifier,
      password
    ]
  }
  ...
 }

[ibacalu]

This would be a great feature, especially now that Terraform Modules support for_each

[rjcoelho]

My main use case is prevent_destroy on DDB and S3, both persistent end-user data that I want to preserve against the accidental replacement of objects

[Shocktrooper]

Good addition as more and more people are starting to use modules like resources so being able to use the lifecycle block on the module level would be amazing

[chancez]

It feels like having lifecycle blocks support dynamic configuration in general would be better than adding support for lifecycle blocks I modules. It would mean modules wouldn't need special support for this, and instead vars and custom logic could be used to set different lifecycle options on resources inside the module (ensuring you can encapsulate the logic, which the approach suggested in this ticket doesn't allow for).

[nitmatgeo]

Hi @antonbabenko, any possibility considering below request?
#28913

[jbdevprimary]

This would also be incredibly helpful for preventing things from ever being part of a destroy