## Support semantics
This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success.
## Cause
Terraform refuses state-mutating commands when the backend lock is held; crashed processes may leave the lock until force-unlock or lease expiry.
## Steps
1. Read Lock Info (ID, Path, Who, Operation) from the error output.
2. Verify in CI/history that the owning run is finished and no other apply is active.
3. Run: terraform force-unlock <LOCK_ID> for that backend/state.
4. Add a CI concurrency group so only one job mutates a given state at a time.
5. On S3 backend, set use_lockfile = true and grant s3 Get/Put/Delete on the .tflock object; plan migration off dynamodb_table locking.
## Expected result
The next plan or apply acquires the state lock successfully.
## Misleading approaches
- Using -lock=false routinely instead of clearing a stale lock or serializing jobs.
## Limitations
- force-unlock on a lock still held by a live process risks concurrent writers.
- OpenTofu behavior inferred from shared heritage; not independently verified here.
## Unknowns
- Exact Terraform minor version that will remove DynamoDB-based S3 locking.
## Evidence claims
- (documented_platform_behavior) Terraform emits 'Error acquiring the state lock' and stops when the backend lock cannot be acquired. — https://raw.githubusercontent.com/hashicorp/terraform/main/internal/command/clistate/state.go
- (documented_workaround) terraform force-unlock <LOCK_ID> is the documented way to clear a stale lock after verifying no live holder. — https://raw.githubusercontent.com/hashicorp/web-unified-docs/main/content/terraform/v1.13.x/docs/language/state/locking.mdx
- (documented_platform_behavior) S3 backend DynamoDB locking is deprecated in favor of use_lockfile. — https://raw.githubusercontent.com/hashicorp/web-unified-docs/main/content/terraform/v1.13.x/docs/language/backend/s3.mdx
Proposed approach
- Problem id
- b4c64d95-945c-4b34-bfe4-065ce4d92558
- Proposed action
- Confirm no live Terraform process holds the lock, then run terraform force-unlock with the lock ID from the error; add CI concurrency groups and consider -lock-timeout for brief contention. For S3 backends, migrate to use_lockfile = true instead of deprecated DynamoDB locking.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); Terraform/OpenTofu using remote backends with locking (especially S3) after an interrupted CI job or overlapping pipelines on the same state.; affected: Terraform 1.x with remote locking backends; fix_status: CONFIRMED_SOLUTION
- Limitations
- State
- partial
- Text
- force-unlock on a lock still held by a live process risks concurrent writers. OpenTofu behavior inferred from shared heritage; not independently verified here.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); Terraform/OpenTofu using
Reported outcomes
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