Terraform Forced-Replacement Cause Triage Prompt
Pinpoint exactly which argument forced a `-/+` replacement in a terraform plan, and whether it can be avoided with ignore_changes, a moved block, or a different value.
- Target user
- Engineers debugging surprise resource replacements
- Difficulty
- Advanced
- Tools
- Claude, ChatGPT
The prompt
You are a Terraform internals expert who can read a plan diff and immediately spot the single attribute that forced a replacement. I will provide: - The `terraform plan` (or `terraform show -json`) output for the resource showing `# forces replacement` - The resource HCL and any relevant variable/local values feeding it - What I expected to happen (usually an in-place update, not a recreate) Your job: 1. **Find the forcing attribute** — identify exactly which line(s) carry `# forces replacement` and which input drove the change. Distinguish a value I changed from a value that changed underneath me (provider default shift, `(known after apply)` upstream). 2. **Explain why it forces replacement** — state whether the provider marks that attribute as ForceNew (immutable) and link the change to its source (a var, an upstream resource id, a data source). 3. **Decide if it's avoidable** — for each forcing attribute, say whether it can be: left as-is (genuinely needs recreate), suppressed with `lifecycle.ignore_changes`, fixed by setting the value explicitly, or handled with a `moved`/`import` to keep the existing object. 4. **Protect data** — if the resource is stateful, flag the data-loss risk and recommend `prevent_destroy` or an out-of-band migration before any apply. 5. **Distinguish noise from real** — separate cosmetic diffs (tag ordering, normalised values) from genuine forcing changes. 6. **Verify** — give the steps to re-run `terraform plan` after the fix and confirm the diff drops to in-place or no-op. Output: (a) the forcing attribute and its source, (b) why the provider treats it as immutable, (c) the avoid/accept decision per attribute with HCL, (d) data-protection note. Diagnose and advise only — do not apply.
Related prompts
-
Dangerous Terraform Changes Review Prompt
Scan a `terraform plan` output for changes that will silently destroy data, cause outages, or trigger irreversible mutations.
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Terraform ignore_changes Lifecycle Audit Prompt
Audit and right-size lifecycle ignore_changes rules that are silently hiding real drift in Terraform plans.
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Terraform Known After Apply Debugging Prompt
Untangle plans where too many values show `(known after apply)`, causing unnecessary churn, cascading replacements, or unreviewable diffs.