Ignore autoscaling changes

For platform engineers deciding whether to apply lifecycle_ignore_autoscaling_changes: what it changes, how to enable it, and how to check it worked.

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

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

Affected resources

Before and after

Before (a module without the change):

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.

The example above is illustrative. To see this rule run for real, open it in the Rules Playground: it applies lifecycle_ignore_autoscaling_changes to a reviewed upstream module that declares the resources this rule targets, and shows the diff the registry would serve. No account needed.

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

Limitations this rule answers

Per-module pages under Workarounds where this rule is the answer, each with the native workaround first and the diff the rule makes:

• DynamoDB table: DynamoDB read and write capacity reverts on every plan

Default configuration

These are the values the rule ships with. Parameters never travel in a module source URL, so a rule named there runs with exactly these defaults. Your organization sets them per rule, in its Baseline or in a ruleset.

The HCL this rule is written in, with its parameters and the transformers it runs, is published at lifecycle_ignore_autoscaling_changes.

How to enable

On a framework host, add the rule on top of your organization's Baseline with ?add_rules= in the HTTPS module source:

module "dynamodb_table" {
  source = "https://soc2.compliance.tf/terraform-aws-modules/dynamodb-table/aws?version=x.y.z&add_rules=lifecycle_ignore_autoscaling_changes"
}

On your organization's host, an org admin adds the rule to the Baseline, which reaches every module served from that host, or to a named ruleset that a module selects with ?ruleset=:

module "dynamodb_table" {
  source = "https://bobthecorp.compliance.tf/terraform-aws-modules/dynamodb-table/aws?version=x.y.z&ruleset=<ruleset-name>"
}

Replace x.y.z with the release you use and bobthecorp with your organization's alias. Which parameters each host accepts, and which it refuses with a 400, is on Rulesets in the console.

How to check it worked

Read compliancetf-manifest.json in the module you received. Its entry for this rule carries an outcome: enforced means the change was made, not_applicable means nothing matched - no resource of a targeted type, or the module already carried the identical change. Do not infer enforcement from a successful terraform init; a rule that changes nothing also inits cleanly.

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.
• Works with Terraform 1.x and OpenTofu 1.6 and later. The rule reads ordinary HCL, and anything it changes stays ordinary HCL.

Failure modes

Related

• DynamoDB table workarounds
• Ignore tag changes
• Ignore AMI changes
• Rulesets in the console - where an org admin adds this rule to the Baseline or a ruleset
• Rule catalog - every rule, with what each one changes