fix(ci): serialize AWS and GCP Terraform state writers on environment, not branch

.github/workflows/cleanup-staging.yml

@@ -98,6 +98,13 @@ jobs:
     name: Destroy AWS Lambda (staging)
     runs-on: ubuntu-24.04-arm
     needs: guard
+    # Shares s3://<bucket>/github-staging/terraform.tfstate with
+    # deploy-aws-lambda.yml and rollback.yml, so it shares their concurrency
+    # group: one writer per state file, whatever workflow or ref it came from
+    # (#1806). The suffix is a literal because this job's state key is too.
+    concurrency:
+      group: aws-tfstate-staging
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read
@@ -175,6 +182,14 @@ jobs:
     name: Destroy AWS Fargate (staging)
     runs-on: ubuntu-24.04-arm
     needs: guard
+    # Shares s3://<bucket>/github-fargate-staging/terraform.tfstate with
+    # deploy-aws-fargate.yml, so it shares that workflow's concurrency group
+    # (#1806). This is a different state object from destroy-aws-lambda's
+    # above, so the two jobs are deliberately in different groups and may run
+    # concurrently. The suffix is a literal because this job's state key is too.
+    concurrency:
+      group: aws-fargate-tfstate-staging
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read
@@ -322,6 +337,13 @@ jobs:
     name: Destroy GCP (staging)
     runs-on: ubuntu-latest
     needs: guard
+    # Shares gs://<bucket>/github-staging/default.tfstate with deploy-gcp.yml
+    # and rollback.yml, so it shares their concurrency group (#1806). This job
+    # writes state twice: the `terraform state rm` calls below as well as the
+    # destroy. The suffix is a literal because this job's backend prefix is too.
+    concurrency:
+      group: gcp-tfstate-staging
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read

.github/workflows/deploy-all.yml

@@ -50,6 +50,14 @@ on:
   release:
     types: [created]
 
+# None of the four `uses:` caller jobs below carries a `concurrency` group, and
+# that is deliberate (#1801, #1806). The Terraform state guard is the group on
+# each called workflow's own deploying job, which runs as a real job of THIS run
+# and is serialized there. Putting the same group on a caller job would deadlock:
+# the caller would hold the group while waiting on the inner job queued behind
+# it. GitHub documents the sibling hazard for `cancel-in-progress: true` (sharing
+# a group between caller and called cancels the already-running caller); at
+# `false` it stalls instead. The per-job note on `deploy-azure` spells this out.
 jobs:
   # Determine deployment strategy
   determine-deployment:

.github/workflows/deploy-aws-fargate.yml

@@ -25,10 +25,13 @@ permissions:
   id-token: write
   contents: read
 
-concurrency:
-  group: deploy-fargate-${{ github.ref }}
-  cancel-in-progress: false
-
+# No workflow-level `concurrency` on purpose. What needs protecting is the
+# Terraform state object, which is keyed on the environment, and only the
+# job-level key can see `needs.prepare.outputs.environment` -- this level is
+# limited to the `github`, `inputs` and `vars` contexts. Keying it on
+# `github.ref` put two runs on different refs that both resolve to the same
+# environment into different groups against one state file (#1806). The group
+# lives on `deploy` below.
 on:
   workflow_dispatch:
     inputs:
@@ -113,6 +116,21 @@ jobs:
     name: Deploy to Fargate
     runs-on: ubuntu-24.04-arm
     needs: prepare
+    # Every run that writes
+    # s3://<bucket>/github-fargate-<environment>/terraform.tfstate serializes
+    # here, whatever ref or workflow it came from (#1806). This is a DIFFERENT
+    # state object from the Lambda one (github-<environment>/), so it takes its
+    # own group rather than sharing `aws-tfstate-*`; sharing would serialize two
+    # independent state files against each other for no gain. The suffix is the
+    # exact value the backend key below is built from, and `prepare` fails the
+    # run on anything outside dev|staging|prod so it can never be empty.
+    #
+    # `cancel-in-progress: false` is stated rather than left to the default:
+    # cancelling mid-`terraform apply` is how you get a half-applied stack and a
+    # lock nobody releases.
+    concurrency:
+      group: aws-fargate-tfstate-${{ needs.prepare.outputs.environment }}
+      cancel-in-progress: false
     outputs:
       alb_url: ${{ steps.outputs.outputs.alb_url }}
       service_name: ${{ steps.outputs.outputs.service_name }}

.github/workflows/deploy-aws-lambda.yml

@@ -30,10 +30,13 @@ name: Deploy to AWS Lambda
 permissions:
   contents: read
 
-concurrency:
-  group: deploy-lambda-${{ github.ref }}
-  cancel-in-progress: false
-
+# No workflow-level `concurrency` on purpose. What needs protecting is the
+# Terraform state object, which is keyed on the environment, and only the
+# job-level key can see `needs.prepare.outputs.target_environment` -- this level
+# is limited to the `github`, `inputs` and `vars` contexts. Keying it on
+# `github.ref` put two runs on different refs that both resolve to the same
+# environment into different groups against one state file (#1806). The group
+# lives on `build-and-deploy` below.
 on:
   push:
     branches: [main]
@@ -206,6 +209,18 @@ jobs:
       # change none of this repo's Environments have any. See #1648.
       id-token: write
       contents: read
+    # Every run that writes s3://<bucket>/github-<environment>/terraform.tfstate
+    # serializes here, whatever ref or workflow it came from (#1806). The suffix
+    # is the exact value the backend key below is built from, so the group and
+    # the state object cannot drift apart, and `prepare` fails the run on
+    # anything outside dev|staging|prod so it can never be empty.
+    #
+    # `cancel-in-progress: false` is stated rather than left to the default:
+    # cancelling mid-`terraform apply` is how you get a half-applied stack and a
+    # lock nobody releases.
+    concurrency:
+      group: aws-tfstate-${{ needs.prepare.outputs.target_environment }}
+      cancel-in-progress: false
     # Bind to the named GitHub Environment matching the target so
     # secrets.* resolve to environment-scoped values when defined,
     # falling back to repo-scoped secrets otherwise. Without this,
@@ -280,18 +295,19 @@ jobs:
           cd terraform/environments/aws
           terraform apply -auto-approve tfplan
 
-      - name: Release state lock on failure
-        if: failure() || cancelled()
-        env:
-          TF_BACKEND: ${{ secrets.TF_BACKEND_AWS }}
-          ENVIRONMENT: ${{ needs.prepare.outputs.target_environment }}
-        run: |
-          BUCKET=$(grep -E '^\s*bucket\s*=' /tmp/backend.tfbackend 2>/dev/null | tr -d ' "' | cut -d= -f2)
-          if [ -n "$BUCKET" ]; then
-            LOCK_KEY="github-${ENVIRONMENT}/terraform.tfstate.tflock"
-            echo "Releasing S3 state lock: s3://${BUCKET}/${LOCK_KEY}"
-            aws s3 rm "s3://${BUCKET}/${LOCK_KEY}" 2>/dev/null || echo "No lock file found (already clean)"
-          fi
+      # No automatic state-lock release on failure. The step that used to live
+      # here ran on `failure() || cancelled()` with no age check and no check
+      # that the lock was this run's, so it deleted whatever lock object was
+      # there. The `cancelled()` half is the decisive one: GitHub runs those
+      # steps while `terraform apply` is still shutting down and may still be
+      # writing state, so it destroyed a lock out from under an active writer.
+      # A run that failed *because* it could not acquire the lock would also
+      # have deleted the lock held by the run still applying. Removed with
+      # #1806, matching the shape deploy-aws-fargate.yml already uses.
+      # Terraform releases its own lock on a clean apply error; a lock that
+      # survives a run means the run died abnormally, which needs operator
+      # confirmation that the owning run is dead. Recovery is
+      # `terraform force-unlock <ID>` -- see runbooks/terraform-stuck-lock.md.
 
       - name: Get Terraform outputs
         id: outputs

.github/workflows/deploy-gcp.yml

@@ -24,10 +24,13 @@ permissions:
   id-token: write
   contents: read
 
-concurrency:
-  group: deploy-gcp-${{ github.ref }}
-  cancel-in-progress: false
-
+# No workflow-level `concurrency` on purpose. What needs protecting is the
+# Terraform state object, which is keyed on the environment, and only the
+# job-level key can see `needs.prepare.outputs.environment` -- this level is
+# limited to the `github`, `inputs` and `vars` contexts. Keying it on
+# `github.ref` put two runs on different refs that both resolve to `dev` into
+# different groups against one state file (#1806). The group lives on
+# `build-and-deploy` below.
 on:
   push:
     branches: [main]
@@ -115,6 +118,18 @@ jobs:
     name: Build & Deploy
     runs-on: ubuntu-latest
     needs: prepare
+    # Every run that writes gs://<bucket>/github-<environment>/default.tfstate
+    # serializes here, whatever ref or workflow it came from (#1806). The suffix
+    # is the exact value the backend prefix below is built from, so the group and
+    # the state object cannot drift apart, and `prepare` fails the run on
+    # anything outside dev|staging|prod so it can never be empty.
+    #
+    # `cancel-in-progress: false` is stated rather than left to the default:
+    # cancelling mid-`terraform apply` is how you get a half-applied stack and a
+    # lock nobody releases.
+    concurrency:
+      group: gcp-tfstate-${{ needs.prepare.outputs.environment }}
+      cancel-in-progress: false
     outputs:
       service_url: ${{ steps.deploy.outputs.service_url }}
 
@@ -136,18 +151,20 @@ jobs:
         with:
           terraform_version: ${{ env.TF_VERSION }}
 
+      # This step used to `gsutil rm` the state lock object before every init,
+      # unconditionally and with no check that the lock was stale or anyone
+      # else's, so it deleted a live lock held by a concurrent writer. Removed
+      # with #1806; the job-level `concurrency` group above is what keeps
+      # writers apart now, and a loud "Error acquiring the state lock" is the
+      # correct outcome if one ever slips through. Recovery from a genuinely
+      # stranded lock is `terraform force-unlock <ID>` -- see
+      # runbooks/terraform-stuck-lock.md.
       - name: Terraform Init
         env:
           TF_BACKEND: ${{ secrets.TF_BACKEND_GCP }}
           ENVIRONMENT: ${{ needs.prepare.outputs.environment }}
         run: |
           printf '%s\nprefix = "github-%s"\n' "$TF_BACKEND" "$ENVIRONMENT" > /tmp/backend.tfbackend
-          # Break any stale state lock from a previous failed run
-          BUCKET=$(grep -E '^\s*bucket\s*=' /tmp/backend.tfbackend 2>/dev/null | tr -d ' "' | cut -d= -f2)
-          if [ -n "$BUCKET" ]; then
-            LOCK_FILE="gs://${BUCKET}/github-${ENVIRONMENT}/default.tflock"
-            gsutil rm "${LOCK_FILE}" 2>/dev/null || true
-          fi
           cd terraform/environments/gcp
           terraform init -backend-config=/tmp/backend.tfbackend
 
@@ -173,17 +190,16 @@ jobs:
           SERVICE_URL=$(terraform output -raw cloud_run_service_url 2>/dev/null | grep -v '::' || echo "")
           echo "service_url=$SERVICE_URL" >> $GITHUB_OUTPUT
 
-      - name: Release state lock on failure
-        if: failure() || cancelled()
-        env:
-          ENVIRONMENT: ${{ needs.prepare.outputs.environment }}
-        run: |
-          BUCKET=$(grep -E '^\s*bucket\s*=' /tmp/backend.tfbackend 2>/dev/null | tr -d ' "' | cut -d= -f2)
-          if [ -n "$BUCKET" ]; then
-            LOCK_FILE="gs://${BUCKET}/github-${ENVIRONMENT}/default.tflock"
-            echo "Releasing GCS state lock: ${LOCK_FILE}"
-            gsutil rm "${LOCK_FILE}" 2>/dev/null || echo "No lock file found (already clean)"
-          fi
+      # No automatic state-lock release on failure. The step that used to live
+      # here ran on `failure() || cancelled()` with no age check and no check
+      # that the lock was this run's, so it deleted whatever lock object was
+      # there. The `cancelled()` half is the decisive one: GitHub runs those
+      # steps while `terraform apply` is still shutting down and may still be
+      # writing state, so it destroyed a lock out from under an active writer.
+      # Terraform releases its own lock on a clean apply error; a lock that
+      # survives a run means the run died abnormally, which needs operator
+      # confirmation that the owning run is dead. Recovery is
+      # `terraform force-unlock <ID>` -- see runbooks/terraform-stuck-lock.md.
 
       - name: Save deployment info
         run: |

.github/workflows/destroy-fargate-dev.yml

@@ -75,6 +75,15 @@ jobs:
     name: Terraform Destroy (Fargate dev)
     runs-on: ubuntu-24.04-arm
     needs: guard
+    # Destroys s3://<bucket>/github-fargate-dev/terraform.tfstate, the same
+    # state object deploy-aws-fargate.yml and cleanup-staging.yml write, so it
+    # takes the same concurrency group: one writer per state file, whatever
+    # workflow or ref it came from (#1806). The suffix is a literal because this
+    # job's state key is too. `cancel-in-progress: false` because cancelling
+    # mid-`terraform destroy` leaves a half-destroyed stack and a stuck lock.
+    concurrency:
+      group: aws-fargate-tfstate-dev
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read
@@ -103,15 +112,19 @@ jobs:
         with:
           terraform_version: ${{ env.TF_VERSION }}
 
+      # This step used to `aws s3 rm` the state lock object before every init,
+      # unconditionally and with no check that the lock was stale or anyone
+      # else's, so it deleted a live lock held by a concurrent writer. Removed
+      # with #1806; the job-level `concurrency` group above is what keeps
+      # writers apart now, and a loud "Error acquiring the state lock" is the
+      # correct outcome if one ever slips through. Recovery from a genuinely
+      # stranded lock is `terraform force-unlock <ID>` -- see
+      # runbooks/terraform-stuck-lock.md.
       - name: Terraform Init
         env:
           TF_BACKEND: ${{ secrets.TF_BACKEND_AWS }}
         run: |
           printf '%s\nkey = "github-fargate-dev/terraform.tfstate"\n' "$TF_BACKEND" > /tmp/backend.tfbackend
-          BUCKET=$(grep -E '^\s*bucket\s*=' /tmp/backend.tfbackend 2>/dev/null | tr -d ' "' | cut -d= -f2)
-          if [ -n "$BUCKET" ]; then
-            aws s3 rm "s3://${BUCKET}/github-fargate-dev/terraform.tfstate.tflock" 2>/dev/null || true
-          fi
           cd terraform/environments/aws
           terraform init -backend-config=/tmp/backend.tfbackend
 

.github/workflows/rollback.yml

@@ -175,6 +175,16 @@ jobs:
     timeout-minutes: 30
     needs: validate
     if: inputs.cloud == 'aws-lambda'
+    # `terraform apply` against s3://<bucket>/github-<environment>/terraform.tfstate,
+    # the same object deploy-aws-lambda.yml and cleanup-staging.yml write, so it
+    # takes the same concurrency group (#1806). `inputs.environment` is a
+    # required `choice` constrained to dev|staging|prod, so the suffix is never
+    # empty; it is the same value this job interpolates into the state key below.
+    # The eviction and approval-gate caveats documented on `rollback-azure` apply
+    # here identically.
+    concurrency:
+      group: aws-tfstate-${{ inputs.environment }}
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read
@@ -263,6 +273,20 @@ jobs:
     timeout-minutes: 30
     needs: validate
     if: inputs.cloud == 'aws-fargate'
+    # NOTE the group is `aws-tfstate-*`, NOT `aws-fargate-tfstate-*`. Despite
+    # the job name, the state key this job builds below is
+    # `github-<environment>/terraform.tfstate` -- the LAMBDA namespace -- not
+    # `github-fargate-<environment>/` as deploy-aws-fargate.yml uses. The group
+    # must name the object this job actually locks, or it would serialize
+    # against a state file it never touches while writing one unguarded, which
+    # is #1806 reproduced in a new place. That namespace mismatch is a real
+    # pre-existing defect (a Fargate rollback applies into the Lambda state),
+    # tracked in #1811 rather than changed here, because moving the key changes
+    # which infrastructure a rollback rewrites. When #1811 lands, this group
+    # moves to `aws-fargate-tfstate-*` in the same commit as the key.
+    concurrency:
+      group: aws-tfstate-${{ inputs.environment }}
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read
@@ -335,6 +359,14 @@ jobs:
     timeout-minutes: 30
     needs: validate
     if: inputs.cloud == 'gcp'
+    # `terraform apply` against gs://<bucket>/github-<environment>/default.tfstate,
+    # the same object deploy-gcp.yml and cleanup-staging.yml write, so it takes
+    # the same concurrency group (#1806). `inputs.environment` is a required
+    # `choice` constrained to dev|staging|prod, so the suffix is never empty; it
+    # is the same value this job interpolates into the backend prefix below.
+    concurrency:
+      group: gcp-tfstate-${{ inputs.environment }}
+      cancel-in-progress: false
     permissions:
       id-token: write
       contents: read