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A Terraform destroy count is a proposed plan result, not proof that Terraform is deleting the right things. Review the resource addresses and actions, confirm the workspace and configuration/state context, and approve only when the proposed target set matches your intent. If generated Terraform has a misplaced comment, first establish whether the file is native .tf or JSON-based .tf.json: their comment rules differ.
Why a Terraform destroy count needs a plan review
Terraform’s plan describes proposed actions. In plan output, + means create, - means destroy, ~ means update in place, and -/+ means replacement. A replacement includes destruction, so do not check only the headline destroy total; inspect each planned address and action.
terraform plan -destroy previews a destroy-mode plan. The terraform destroy command is a convenience form of applying in destroy mode. Destroy mode aims to destroy managed objects represented by the selected configuration, but an unseen plan cannot be validated from its count alone. Terraform plan command and Terraform destroy command document these behaviors.
Check scope before approving
- Compare every planned address with the resources you intend to remove, including numeric
countindexes orfor_eachkeys. - Confirm the active workspace, input values, configuration, and state context are the ones you expect; these determine which instances Terraform plans against.
- Pause if unexpected addresses appear. Investigate why Terraform considers those instances managed or why they are absent from the active configuration before applying.
The plan approval prompt is a consequential checkpoint, not a formality. HashiCorp’s plan tutorial demonstrates reviewing a plan and requesting approval before applying it.
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Inspect machine-readable output carefully
For automation, terraform show -json emits JSON representations of a plan, including configuration and planned changes. Consumers should account for the documented format and version behavior in the Terraform JSON output format. Plan files and their JSON output can contain sensitive values; do not commit them to version control.
Choose between count and for_each by instance identity
Both meta-arguments create multiple instances from one resource or module block, but they identify those instances differently. Use the model that fits the data and the references you need to maintain.
| Choice | Instance identity | Best fit | Important constraint |
|---|---|---|---|
count |
Zero-based numeric index, such as resource.example[0] |
Nearly identical instances when position is an adequate identity | The count must be a whole number known before Terraform performs remote resource operations. |
for_each |
Map key or set member, such as resource.example["api"] |
Instances with meaningful names or arguments associated with distinct keys or values | Accepts a map or a set of strings; expressions use each.key and each.value. |
The two arguments are mutually exclusive within a block. Terraform’s count reference and for_each reference describe their accepted values and instance-address behavior.
Review addresses when changing the repetition model
With count, instances are addressed by position; with for_each, they are addressed by key. If you change how a block is expanded, inspect the resulting addresses and full plan rather than assuming a change in the destroy total is harmless. A planned action against an unexpected index or key is a reason to stop and check the configuration and state relationship.
Put comments in the right Terraform file and location
Terraform configuration can use native syntax in .tf files or JSON syntax in .tf.json files. The JSON form is primarily intended for programmatic generation and consumption, rather than hand editing. Terraform JSON configuration syntax explains the distinction and the limited comment convention.
In generated .tf.json, use the special property only in supported objects
Terraform ignores a property named "//" when it appears in an object representing a block body, and it also permits the property at the configuration root. It is not a general JSON comment syntax: inside an object interpreted as an expression, "//" is an ordinary attribute name. Whether a misplaced property is treated as a comment therefore depends on the kind of object containing it.
{
"resource": {
"aws_instance": {
"example": {
"//": "Generated resource for scheduled tasks",
"instance_type": "t2.micro",
"ami": "ami-abc123"
}
}
}
}Here, the comment property is within the resource block body. If your generated file behaves differently, inspect the surrounding JSON nesting and determine whether that object is a block body or an expression; without the file, it is not possible to identify a specific parse error.
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In native .tf, use HCL comment syntax
Native Terraform files accept # and // line comments, as well as /* ... */ block comments. The style guide recommends # as the default idiom. See Terraform language style.
Quick Recap
Validate generated configuration and inspect the plan
- Identify the file format. Check whether the generated artifact ends in
.tfor.tf.jsonand use the corresponding syntax rules. - Inspect comment nesting. In JSON configuration, verify that each
"//"property is at the root or in a block-body object, not an expression object. - Check instance identity. Determine whether the block uses
countorfor_each, then review references and planned addresses against the intended indexes or keys. - Run the appropriate checks. Use
terraform fmtandterraform validateas applicable to the configuration. These checks do not replace review of the proposed plan. See the fmt command and validate command. - Review the complete plan before applying. Confirm every destroy and replacement action, along with the workspace and configuration/state context, before approving.
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