exercise_cluster

Exercise Cluster Skill

Goal: Find bugs in the multigres operator and upstream multigres by deploying real MultigresCluster configurations, mutating them through operator-driven workflows, and using the observer to verify true end-to-end cluster health.

Core principles:

• The observer is the single source of truth for cluster health. CRD phase Healthy is necessary but NOT sufficient — it misses broken replication, connection failures, and multi-primary states.
• You drive kubectl directly. Read the live CR, understand its structure, construct correct patches. Fixtures have different structures (.spec.pools vs .overrides.pools).
• Every post-grace-period error is potentially a real bug. NEVER dismiss errors — operator logs, RBAC warnings, webhook warnings, kubectl output. Investigate everything, report everything, including transient findings that resolved.

Phase 0: Cluster Setup

Verify the kind cluster and observer are running:

KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl cluster-info
KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl get pods -l app.kubernetes.io/name=multigres-observer -n multigres-operator

If cluster is down: make kind-deploy. If only observer is missing: make kind-deploy-observer.

Define the observer helper:

observer() {
  KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl exec -n multigres-operator deploy/multigres-observer -- curl -sf "http://localhost:9090$1"
}

Verify: observer /api/status | jq '.summary'

Phase 1: Deploy Fixture & Baseline

Pick a fixture from Fixture Selection below. For topology fixtures, read references/topology-awareness.md first.

1. Deploy prerequisites if they exist, wait for pods to be Running:

   KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl apply -f fixtures/<fixture>/prerequisites.yaml
   

2. Deploy the cluster. Read the kubectl output — webhook warnings mean real problems. Stop and fix before proceeding.

   KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl apply -f fixtures/<fixture>/cluster.yaml
   

3. Run the Stability Verification Protocol (below) with tier lifecycle. Baseline must be fully clean — any error is a bug.
4. For template/override fixtures: run references/template-verification.md.

Phase 2: Mutation Testing

Consult references/scenarios/index.md for the full scenario catalog. For each scenario:

1. Read the live CR: KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl get multigrescluster <name> -n <ns> -o yaml
2. Save pre-mutation state for teardown.
3. Construct and apply the correct patch based on the actual CR.
4. Verify using the appropriate protocol:
   • Fast-path eligible → references/fast-path-verification.md
   • Concurrent mutations → references/concurrent-mutations.md
   • Negative assertions → references/negative-assertions.md
   • All others → Stability Verification Protocol below
5. Log results, teardown if applicable, verify stability again. Proceed only after confirmed stable.

Stability Verification Protocol

Run after EVERY cluster change: deploy, mutation, teardown.

Tiers

Step 1 — CRD Phase Gate

Poll .status.phase every 5s until Healthy:

KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl get multigrescluster <name> -n <ns> -o jsonpath='{.status.phase}'

If Degraded/Failed persists >2 min or timeout reached → STOP, investigate.

Step 2 — Grace Period

The observer suppresses pool pod errors for 2 min after creation. Wait until ALL pool pods are at least 150s old:

KUBECONFIG=$(pwd)/kubeconfig.yaml kubectl get pods -n <ns> -l app.kubernetes.io/component=shard-pool \
  -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.metadata.creationTimestamp}{"\n"}{end}'

Step 3 — Stability Observation

Poll every 10s, tracking: consecutive_clean (polls with 0 errors/fatals), all_findings (every error/fatal seen), elapsed.

observer /api/status | jq '{
  summary: .summary,
  errors: [(.findings // [])[] | select(.level == "error" or .level == "fatal")],
  warns: [(.findings // [])[] | select(.level == "warn")]
}'

Exit conditions:

A finding "persists" when the same check+component appears in consecutive polls. Use /api/history to classify.

Step 4 — Result Classification

• STABLE (clean): No findings during observation.
• STABLE (transients observed): Errors appeared then resolved. List each with check, component, message, duration. Report these — they may indicate intermittent bugs.
• UNSTABLE: Persistent errors. Investigate via references/deep-investigation.md.

Step 5 — Post-Stability Checks

Run all three after stability is confirmed:

Warn review:

observer /api/status | jq '[(.findings // [])[] | select(.level == "warn")]'

Note persistent warnings (replication lag, WAL replay paused).

Primary verification — catches stale podRoles bugs:

# Exactly 1 PRIMARY per pool per cell in CRD
kubectl get shard -n <ns> -o json | jq '[.items[].status.podRoles | to_entries[] | select(.value == "PRIMARY")] | length'

# Cross-reference with actual PG state
for pod in $(kubectl get pods -n <ns> -l app.kubernetes.io/component=shard-pool -o name); do
  echo -n "$pod: "
  kubectl exec -n <ns> $pod -c postgres -- psql -h 127.0.0.1 -p 5432 -U postgres -tAc "SELECT CASE WHEN pg_is_in_recovery() THEN 'REPLICA' ELSE 'PRIMARY' END"
done

CRD PRIMARY must match SQL pg_is_in_recovery() = false. Mismatch → trigger reconcile, report as "error".

Observer history assertion:

observer /api/history | jq '{persistent: .persistent, flapping: .flapping, transientCount: (.transient | length)}'

Assert persistent == [] and flapping == []. Investigate before proceeding if not.

Execution Modes

Default to core when unspecified.

Fixture Selection

Prerequisites are self-contained (except s3-backup). Deploy prereqs first, wait for pods Running.

Recommended order: minimal-retain → minimal-delete → templated-full → overrides-complex → external-etcd-mixed → multi-cell-topology

Reporting

Create report at agent-docs/exerciser/exercise-run-<YYYY-MM-DD-HHMMSS>.md:

• Environment (cluster, observer, operator image, multigres images)
• Per-fixture: baseline, each scenario (mutation, stability result, all findings, teardown)
• Summary: fixtures tested, scenarios run, bugs found, transients observed

Reference Documents