Ignore Autoscaling Changes

Adds ignore_changes = [read_capacity, write_capacity] to DynamoDB tables. Prevents Terraform from reverting autoscaler adjustments.

Why this rule exists

DynamoDB tables with auto scaling enabled have their read and write capacity adjusted continuously by AWS Application Auto Scaling. Terraform sees these changes on every plan and proposes reverting them.

The fix is straightforward (add ignore_changes) but requires modifying every DynamoDB resource in every module. With upstream terraform-aws-modules, you cannot add this without forking.

Related Terraform and OpenTofu issues

Affected resources

What this rule does

Adds a lifecycle { ignore_changes = [...] } block to each matching resource. Terraform and OpenTofu will ignore external changes to the listed attributes on subsequent plans.

Ignored attributes: read_capacity, write_capacity

Before and after

Before (upstream module):

resource "aws_dynamodb_table" "this" {
  # ... resource configuration ...

  tags = var.tags
}

After (with Ignore Autoscaling Changes applied):

resource "aws_dynamodb_table" "this" {
  # ... resource configuration ...

  tags = var.tags

  lifecycle {
    ignore_changes = [read_capacity, write_capacity]
  }
}

The only change is the rule transformation. All existing arguments, outputs, and module behavior remain identical.

Known limits

• Only affects aws_dynamodb_table. Does not cover aws_dynamodb_global_table or other DynamoDB resources.
• Does not ignore changes to other auto-scaled attributes like GSI capacity.
• Only .tf and .tofu files are read. Modules written in JSON syntax (.tf.json, .tofu.json) are left untouched.
• Only the module's own directory and its first-level modules/* submodules are processed. Modules that this module calls by source URL are separate downloads and are handled on their own request.

Default configuration

These are the values the rule ships with. They are not settable from a module source URL: ?rules= carries rule names only, so a per-request enable uses exactly the defaults below. Your organization sets them per rule, in its Baseline or in a ruleset, from the Operational Rules page; see Baseline rules and rulesets.

How to enable

On a framework host, per request:

Add ?rules=lifecycle_ignore_autoscaling_changes to your HTTPS module source. Use the full namespaced id. A bare lifecycle_ignore_autoscaling_changes matches no rule: it is skipped server-side and your terraform init still succeeds, without the rule.

module "example" {
  source = "https://soc2.compliance.tf/terraform-aws-modules/s3-bucket/aws?version=5.0.0&rules=lifecycle_ignore_autoscaling_changes"
}

On your organization's host:

Add the rule to the organization's Baseline, which applies to every module served from the bare organization form <alias>.compliance.tf/<namespace>/<name>/<provider>, or to a named ruleset that one module selects with ?ruleset=<name> on the HTTPS form of that address. A project environment (<alias>.compliance.tf/<project>/<env>/<module>) serves the rules frozen in its bound snapshot instead: there the rule goes into the config draft and reaches the environment by promotion. On both organization forms ?rules= is refused with a 400 — including the subtractive - prefix — rather than dropped, so you cannot mistake an ignored override for an applied one. Change the configuration, not the URL. See Baseline rules and rulesets for the configuration flow, and registry resolution for how the address forms differ.

Failure modes