rustfs/docs/operations/kms-observability-runbook.md

KMS observability runbook

This runbook covers the KMS metrics, the Grafana dashboard that visualizes them, and the response procedure for each Prometheus alert shipped in .docker/observability/prometheus-rules/rustfs-kms-alerts.yml. It is the runbook_url target for those alerts. For what each KMS backend protects and how Vault authentication behaves, see the KMS backend security properties and the Vault KMS authentication runbook.

Metric reference

Across every family below, label values are exclusively static enum strings — key identifiers, key material, ciphertext, paths, and tokens never appear in metric labels, and any change that would add such a label is a regression.

Backend operation metrics

All four are emitted at the single operation-policy choke point (crates/kms/src/policy.rs) that every instrumented KMS backend call flows through.

Metric	Type	Labels	Meaning
rustfs_kms_backend_operations_total	counter	operation, op_class, outcome	Operations executed under the operation policy, counted once per terminal outcome
rustfs_kms_backend_attempt_failures_total	counter	operation, error_class	Individual failed attempts, including attempts the retry policy later absorbed
rustfs_kms_backend_operation_duration_seconds	histogram	operation, outcome	Wall-clock duration of a whole operation, including retries and backoff sleeps
rustfs_kms_backend_operation_attempts	histogram	operation, outcome	Number of attempts one operation used before completing

Label values:

• outcome: success, fatal (a non-retryable failure ended the operation on first observation), budget_exhausted (the attempt budget ran out on retryable failures), deadline_exceeded (the operation deadline ran out before another attempt could complete), cancelled (shutdown or caller cancellation).
• op_class: read_idempotent (safe to retry), mutating_non_idempotent (never replayed — a retryable failure terminates after a single attempt because the server may have processed the request), auth (login and token renewal).
• error_class: retryable_conn (connection-level failure: dial, TLS, broken connection), retryable_status (retryable backend status, e.g. Vault 5xx or a sealed Vault's 503), attempt_timeout (the per-attempt timeout cut the attempt off; retried like a connection failure because the server may still have processed the request), fatal (non-retryable: authentication, permissions, malformed request, missing key or version).
• operation: static per-call-site names, e.g. vault_kv2_read_key_version, vault_kv2_cas_write_key, vault_transit_encrypt, vault_transit_decrypt, vault_login, vault_token_renew.

Instrumentation boundary: the Local and Static backends do not flow through the choke point and emit no operation metrics; bringing them under the same instrumentation is tracked separately (rustfs/backlog#1569). Absence of these four series on a cluster using those backends is expected, not an outage. The families below sit above the backend layer and are emitted regardless.

Key metadata cache metrics

Emitted by the manager-level key metadata cache (crates/kms/src/cache.rs), which every backend shares. Publication is gated by the cache's enable_metrics setting, which defaults to on and which no configure-request field sets today, so in practice these are always published. The counters behind the admin status API are maintained either way, so the switch could never blind kms service-status.

Metric	Type	Labels	Meaning
rustfs_kms_metadata_cache_lookups_total	counter	result	Key metadata lookups, by hit or miss
rustfs_kms_metadata_cache_evictions_total	counter	cause	Entries dropped from the cache, by removal cause
rustfs_kms_metadata_cache_entries	gauge	—	Entries the cache currently holds

cause is expired (TTL), size (capacity), explicit (invalidated by a key lifecycle operation), or replaced (overwritten by a newer value). Only expired and size are true evictions — a sustained explicit/replaced rate is lifecycle traffic, not cache pressure.

The entry gauge is republished from every write path and from lookups that miss, because TTL expiry drops entries without any write taking place; a cache that goes completely idle can therefore hold a stale value until the next lookup. Note also that this cache only serves key metadata reads such as describe_key — encrypt, decrypt and data key generation never consult it, so a low hit ratio is not a data-path problem.

Key lifecycle metrics

Published by the background deletion worker (crates/kms/src/deletion_worker.rs) at the end of each sweep, derived from the pages the sweep already walks, so observing the lifecycle costs no extra backend call. The worker only runs on backends whose capabilities include schedule_deletion, so a deployment on a backend without it emits none of these.

Metric	Type	Labels	Meaning
rustfs_kms_pending_deletion_keys	gauge	—	Keys scheduled for deletion whose deadline has not passed
rustfs_kms_deletion_tombstone_keys	gauge	—	Keys left tombstoned by an interrupted removal, still awaiting the sweep
rustfs_kms_oldest_key_rotation_age_seconds	gauge	—	Seconds since the least recently rotated usable key was rotated, counting from creation for keys never rotated; 0 when there are none
rustfs_kms_deletion_sweep_keys_total	counter	outcome	Keys the sweep acted on, by outcome

outcome is removed, blocked (live configuration — the default key, or a reference reported by the injected checker — still points at the key, so the sweep refuses to remove it), skipped (pending but not yet due, or the state changed between inspection and removal), or failed (the removal attempt failed and is retried next sweep). Every series is emitted at zero from the first sweep on, so a rate() over it is defined immediately.

The three gauges are republished only by a sweep that saw the whole key set; a sweep that could not finish listing leaves the previous, complete values standing rather than understating them. Keys already on their way out are excluded from the rotation-age gauge, so it does not stay pinned high by a key that will never be rotated again.

Vault credential metrics

Published by the Vault credential provider (crates/kms/src/backends/vault_credentials.rs), so they exist only on Vault-backed backends. Both are label-less: there is exactly one credential generation to describe, and the Vault address, mount, auth path and token are all off limits as label values.

Metric	Type	Labels	Meaning
rustfs_kms_vault_token_ttl_seconds	gauge	—	Seconds left before the active Vault token expires; 0 once it has
rustfs_kms_vault_credentials_fail_closed	gauge	—	1 while the provider refuses to hand out its token because it is inside the fail-closed safety window, 0 otherwise

The renewal loop republishes both on a 10-second cadence while it waits, generating no extra Vault traffic, so a scrape landing between refresh cycles never reads a TTL frozen at the last refresh. rustfs_kms_vault_credentials_fail_closed at 1 is the metric form of the fail-closed window described in the Vault KMS authentication runbook: while it is set, Vault-backed operations fail rather than run on a credential that may already be invalid.

Synthetic probe metrics

Published by the background probe worker (crates/kms/src/probe.rs), which generates a data key under a reserved probe key, decrypts it, and compares the material. It runs every RUSTFS_KMS_PROBE_INTERVAL_SECS seconds (default 60, raised to a floor of 5, 0 disables the probe entirely), and the status it publishes is what KMS readiness reads.

Metric	Type	Labels	Meaning
rustfs_kms_probe_rounds_total	counter	result	Probe rounds completed, by success, failure or unsupported
rustfs_kms_probe_failures_total	counter	failure_kind	Failed rounds, by the round-trip stage that failed
rustfs_kms_probe_duration_seconds	histogram	result	Wall-clock duration of one probe round
rustfs_kms_probe_last_success_timestamp_seconds	gauge	—	Unix timestamp of the most recent successful round
rustfs_kms_probe_consecutive_failures	gauge	—	Rounds that have failed since the last success

failure_kind is key_provisioning (the probe key could not be described or created), generate, decrypt, or mismatch — the last means both calls answered but the material did not survive the round trip, which is as serious as an outage and is reported as loudly.

unsupported means the backend cannot host the probe key. It is deliberately counted as its own result and never as a failure, and the worker stops after recording it, so failure-counter alerts stay silent on such deployments; the AWS KMS backend is the case in practice, because it refuses a caller-named create. Note also that rustfs_kms_probe_last_success_timestamp_seconds only ever moves forward on a success, so while the probe fails its age keeps growing — alert on that age, not on the presence of a failure counter.

Export path: the metrics facade feeds the OTel recorder in crates/obs, which exports over OTLP to the collector scraped by Prometheus. Histograms therefore appear in Prometheus as _bucket/_sum/_count series. None of these metrics carry the RustFS server label used by the node observability dashboard — distinguish nodes through your scrape topology (job/instance or promoted OTel resource attributes such as service_instance_id).

Dashboard

Import deploy/observability/grafana/rustfs-kms-observability.json into Grafana and select a Prometheus data source that scrapes RustFS metrics. The dashboard has two variables: datasource (Prometheus data source) and operation (multi-select over the operation label). In the docker-compose observability stack (.docker/observability/), dashboards are provisioned from a directory (grafana/provisioning/dashboards/dashboard.yml points at /etc/grafana/dashboards), so no per-file registration is needed there.

The shipped dashboard covers the backend operation metrics only. Its "Planned Panels (TODO)" text panel still describes the cache, lifecycle, Vault credential and probe families as not landed — that panel is stale: the emitting code is merged and the metric names, types and label values are in Metric reference above. Until real panels replace it, query those families ad hoc; nothing in the shipped dashboard or alert rules reads them. See Coverage gaps.

Alert rules

The rules live in .docker/observability/prometheus-rules/rustfs-kms-alerts.yml. The docker-compose Prometheus loads /etc/prometheus/rules/*.yml, so the .yml extension is load-bearing. Validate edits with promtool check rules rustfs-kms-alerts.yml.

Every threshold in that file is a conservative default chosen without a production baseline; see Threshold calibration before treating a firing alert as an SLO breach or a quiet one as health.

Alert response procedures

KmsBackendFatalErrors

Meaning: attempts are failing with error_class="fatal" — failures the policy never retries. Each one is a KMS backend call that failed permanently (authentication, permissions, malformed request, or a missing key/version), so callers are seeing errors right now. This is the highest-signal KMS alert: fatal failures do not appear as background noise in a healthy system.

Investigation:

1. Break the rate down by operation: sum by (operation) (rate(rustfs_kms_backend_attempt_failures_total{error_class="fatal"}[5m])).
2. If the failing operations are vault_login or vault_token_renew (op_class="auth"), the Vault credentials are invalid or expired. Follow the Vault KMS authentication runbook — note that credential refresh is fail-closed, so a broken credential eventually takes down all Vault-backed operations, not just auth. Look for the Vault token renewal failed; falling back to a fresh login and Vault credential refresh failed; retrying until the credentials recover warnings in the RustFS logs; rustfs_kms_vault_credentials_fail_closed at 1, or rustfs_kms_vault_token_ttl_seconds at or near 0, confirms that state without reading logs.
3. If the failing operations are vault_kv2_* or vault_transit_*, check for Vault permission denials: compare the token's policy against the minimal policy in KMS backend security properties (a policy that drifted or was re-scoped produces 403s that classify as fatal), and check the Vault audit log for the corresponding denied requests.
4. A fatal KeyVersionNotFound on decrypt-path operations means a DEK envelope references a key version whose record is missing. Decryption deliberately fails closed with no fallback — see the rotation retention preconditions in KMS backend security properties and verify nobody destroyed version records under the key subtree.
5. Confirm blast radius with the outcome view: sum by (operation) (rate(rustfs_kms_backend_operations_total{outcome="fatal"}[5m])).

Related signals: the "Attempt Failure Rate by Error Class" and "Backend Operation Rate by Outcome" dashboard panels; Vault server audit and server logs; S3-level 5xx on encrypted buckets.

KmsBackendHighErrorRate

Meaning: more than 5% of KMS operations are terminating without success (fatal, budget_exhausted, or deadline_exceeded; cancelled is excluded because shutdown windows legitimately produce it). A traffic guard suppresses the alert below ~0.02 ops/s so a single failure on a near-idle cluster does not page.

Investigation:

1. Break the failures down by outcome: sum by (outcome) (rate(rustfs_kms_backend_operations_total{outcome!~"success|cancelled"}[5m])).
2. If fatal dominates, follow KmsBackendFatalErrors.
3. If budget_exhausted or deadline_exceeded dominates, follow KmsBackendRetryBudgetExhausted — the backend is unavailable or too slow for longer than the retry policy can bridge.
4. Correlate with client impact: encrypted-object PUT/GET failures and S3 error rates on buckets with encryption configured.

Related signals: the "Non-Success Outcome Ratio" dashboard panel; the KMS-related warnings listed under the other alerts in this runbook.

KmsBackendP99LatencyHigh

Meaning: the p99 wall-clock duration of KMS operations is sustained above 2s. The histogram includes retries and backoff sleeps, so a high p99 with a healthy p50 usually means a slow retry tail (a subset of calls failing and being retried), not a uniform slowdown.

Investigation:

1. Compare p50 and p99 on the "Operation Duration p50 / p99" panel. Flat p50 with elevated p99 points at retries; both elevated points at the backend or the network path being uniformly slow.
2. Split by operation with histogram_quantile(0.99, sum by (le, operation) (rate(rustfs_kms_backend_operation_duration_seconds_bucket[5m]))) to see whether one backend call or all of them regressed.
3. Check the attempts histogram: an average meaningfully above 1 confirms the latency is retry-driven; follow KmsBackendAttemptFailureSpike for the failure classes.
4. If latency is not retry-driven, check the network path to Vault (TLS handshakes, DNS, proxies) and Vault's own telemetry (storage backend latency, load).
5. Remember that this latency sits inside S3 request latency for encrypted objects: sustained p99 near the operation deadline will start converting into deadline_exceeded outcomes.

Related signals: the "Operation Duration p99 by Operation" and "Operation Attempts Distribution" panels; KMS backend attempt failed with a retryable error; backing off before retry warnings (fields: operation, attempt, error_class, backoff).

KmsBackendAttemptFailureSpike

Meaning: individual attempts are failing at a sustained rate across all error classes. The retry policy may still be absorbing these — operations can keep succeeding while this alert fires — but the system is burning retry budget and running degraded, and a small further degradation will surface to callers.

Investigation:

1. Break the rate down by class: sum by (error_class) (rate(rustfs_kms_backend_attempt_failures_total[5m])).
2. retryable_conn: network-level failures — check connectivity, TLS, DNS, and whether Vault is down or restarting.
3. retryable_status: the backend answered with a retryable error — check Vault health and seal status (a sealed Vault returns 503, which lands here), and Vault-side rate limiting.
4. attempt_timeout: attempts are being cut off by the per-attempt timeout — either the backend is slow (correlate with KmsBackendP99LatencyHigh) or the configured attempt timeout is too tight for the deployment's network path.
5. fatal: follow KmsBackendFatalErrors.
6. Grep RustFS logs for KMS backend attempt failed with a retryable error; backing off before retry — the structured fields (operation, attempt, error_class, backoff) identify which call sites are cycling.

Related signals: the "Attempt Failure Rate by Error Class" panel; the attempts histogram average rising above 1.

KmsBackendRetryBudgetExhausted

Meaning: operations are terminating as budget_exhausted or deadline_exceeded — every individual failure was retryable, but the backend stayed unhealthy for longer than the retry policy could bridge, so callers received hard failures.

Investigation:

1. Identify the failing operations: sum by (operation) (rate(rustfs_kms_backend_operations_total{outcome=~"budget_exhausted|deadline_exceeded"}[5m])).
2. Establish how long the underlying failure has persisted from the attempt-failure rate history; follow KmsBackendAttemptFailureSpike for the class-specific diagnosis.
3. Note the by-design case: mutating_non_idempotent operations (e.g. vault_kv2_cas_write_key, vault_transit_create_key) are never replayed, so a single retryable failure terminates them as budget_exhausted after one attempt. A spike confined to mutating operations means write-path failures, not an exhausted retry loop.
4. deadline_exceeded clustering with duration p99 near the operation deadline means the budget is being spent on slow attempts rather than fast failures — treat as a latency problem first.
5. Confirm client impact and, if the backend outage is confirmed external (Vault down), coordinate recovery there; RustFS will resume without intervention once the backend recovers.

Related signals: the "Backend Operation Rate by Outcome" panel; retry-backoff warnings in RustFS logs; Vault availability monitoring.

Threshold calibration

Every numeric threshold in rustfs-kms-alerts.yml (5% error ratio, 2s p99, 0.5/s attempt failures, 0.05/s budget exhaustion) is a conservative default chosen without a production baseline, biased toward not paging on healthy-but-busy systems. Before relying on these alerts for paging: run the workload in staging for at least a week, record the steady-state values of the expressions above, then tighten thresholds to sit clearly above observed peaks. Once a stable baseline exists, consider converting KmsBackendAttemptFailureSpike to a baseline-relative form (offset 1d ratio, see .docker/observability/prometheus-rules/rustfs-get-optimization-alerts.yaml for the pattern). Formal SLO targets for KMS operations are deliberately out of scope until that baseline exists (rustfs/backlog#1584).

Coverage gaps

The four metric families designed under rustfs/backlog#1584 — key-cache effectiveness, key lifecycle, Vault credentials, synthetic probe — have all landed and are documented in Metric reference. What is still missing:

• No dashboard panels and no alert rules for those four families. They are emitted but neither visualized nor alerted on, so they surface only in ad-hoc queries. Building against them is safe now: the names and label values above are what the code emits.
• The Local and Static backends emit no operation metrics, because they do not flow through the operation-policy choke point; bringing them under the same instrumentation is tracked separately (rustfs/backlog#1569). Their cache metrics are emitted normally.
• No formal SLO targets, deliberately, until a production baseline exists — see Threshold calibration.

When a panel or alert rule for one of the landed families is added, replace the corresponding TODO bullet in the dashboard's "Planned Panels" text panel and update this section.

Related documents

• KMS backend security properties — backend trust boundaries, minimal Vault policies, rotation retention preconditions.
• Vault KMS authentication runbook — credential sources, refresh behavior, and the fail-closed window.
• deploy/observability/README.md — dashboard import notes for all RustFS dashboards.