22-EFT.WP.Metrology.Instrument v1.0 | Chapter 14 — Runtime Monitoring & SLOs (Health, Drift Alerts)

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Chapter 14 — Runtime Monitoring & SLOs (Health, Drift Alerts)

One-Sentence Objective
Using standardized SLI/SLO and alerting strategies, continuously monitor and close the loop on instrument runtime health, metrological stability, and distribution drift—ensuring long-term availability, traceability, and auditability of the metrology chain.

I. Scope and Objects

1. Scope
   • Long-horizon runtime monitoring for general-purpose instruments accessed via SCPI/IVI in production and lab environments.
   • Covers connection health (session/protocol), data-plane health (throughput/loss/timebase), metrology health (drift/drift rate/uncertainty), and compliance health (manifests/signatures/certificates).
2. Inputs
   • Runtime telemetry: session_open_latency_ms, cmd_roundtrip_ms, throughput_sps, sample_loss_rate, buffer_util, STB/SRQ, err_code.
   • Metrology telemetry: offset/skew/J, u(ts), U = k * u_c, SNR, gain, offset, temp, humidity.
   • Distribution telemetry: psi, KL, W1, q_score.
3. Outputs
   Dashboard metrics panel.instrument.*, SLO assessment reports, tiered alerts and rollback actions, and incremental entries for manifest.instrument.sli.

II. Terms and Variables

• Time & timebase: ts, tau_mono, offset, skew, J, Delta_t.
• Queues & stability: lambda (enqueue rate), mu (service rate), rho = lambda / mu.
• Metrics & budgets: SLI, SLO, p95/p99, alpha_budget (false-alarm budget), downtime_budget.
• Drift measures: psi (population stability index), KL, W1, drift_level, drift_slope.
• Health score: H ∈ [0,1] (higher is better), weights w_i.

III. Postulates P714-*

• P714-1 (Reproducible observations): compute every SLI on a fixed window Delta_t, and record the computation convention and version.
• P714-2 (Unified timebase): aggregate monitoring on tau_mono; publish on ts, and co-record offset/skew/J with u(ts).
• P714-3 (Steady-state first): enforce the steady-state gate rho < 1; violations trigger rate-limiting or graceful degradation.
• P714-4 (Controlled false alarms): use sequential statistics for alerting; monthly false-alarm spend alpha_month ≤ alpha_budget.
• P714-5 (Metrology before throughput): when metrology conflicts with throughput, satisfy U and drift constraints first—even if rate or resolution must be lowered.
• P714-6 (Manifest as source of truth): all monitoring conclusions must be recorded and signed in manifest.instrument.sli.

IV. Minimal Equations S714-*

• S714-1 (Steady state & congestion)
  rho = lambda / mu, require rho < rho_max < 1.
• S714-2 (Health-score aggregation)
  H = 1 - ( w_1 * norm(sample_loss_rate) + w_2 * norm(ts_skew_p95) + w_3 * norm(J_p95) + w_4 * norm(err_rate) + w_5 * norm(drift_level) ), with ∑ w_i = 1.
• S714-3 (EWMA monitoring)
  z_t = lambda_ewma * x_t + ( 1 - lambda_ewma ) * z_{t-1 }, raise a pre-alert when | z_t - mu0 | > L * sigma_z.
• S714-4 (CUSUM drift detection)
  C_t^+ = max( 0, C_{t-1}^+ + ( x_t - mu0 ) - k ); C_t^- = max( 0, C_{t-1}^- + ( mu0 - x_t ) - k ); alert if C_t^+ > h or C_t^- > h.
• S714-5 (Distribution-drift measures)
  psi = ( 1 / B ) * ( ∑ ( ( p_i - q_i ) * ln( p_i / q_i ) ) ) (binned stability index; the convention must be fixed); compute KL and W1 in parallel.
• S714-6 (False-alarm budget consumption)
  alpha_spent = ( ∑ alpha_t ), assert alpha_spent ≤ alpha_budget.

V. Monitoring Procedure M70-14 (Collect → Aggregate → Evaluate → Alert/Rollback → Persist)

1. Metric collection
   Pull runtime and metrology telemetry on a rolling Delta_t window; run align_timebase on ts and summarize offset/skew/J with u(ts).
2. Metric aggregation
   • Compute SLIs: session_open_latency_ms_p95/p99, cmd_roundtrip_ms_p95/p99, throughput_sps, sample_loss_rate, ts_skew_p95, J_p95, err_rate, rho.
   • Compute metrology & distribution metrics: U, SNR, gain/offset drifts, psi/KL/W1.
3. Contract evaluation
   Run assert_instrument_contract plus this chapter’s C70-14*; apply EWMA/CUSUM and account for false-alarm budget.
4. Alerting & rollback
   Tiered triggers: warn → minor → major → critical; enact rate limiting, reconfiguration, session restart, redundant switchover, or publication freeze as appropriate.
5. Manifest persistence
   Write manifest.instrument.sli: window, convention version, metrics, alerts, actions, TraceID, and signature.

VI. Contracts & Assertions C70-14* (Example Threshold Conventions)

• throughput.ok: rho < 0.85 and sample_loss_rate ≤ 1e-4.
• latency.ok: cmd_roundtrip_ms_p99 ≤ 50; session_open_latency_ms_p99 ≤ 1000.
• timebase.ok: |offset| ≤ 1e-6 s, |skew| ≤ 1e-7, J_p95 ≤ 5e-7 s, u(ts)_p95 ≤ 1e-6 s.
• errors.ok: scpi_error_rate ≤ 1e-3, queue_len = 0; SYST:ERR? = 0.
• metrology.stability: |gain_drift| ≤ gain_tol, |offset_drift| ≤ offset_tol, SNR_drop ≤ snr_tol.
• drift.ok: psi ≤ psi_tol and KL ≤ kl_tol and W1 ≤ w1_tol.
• health.ok: H ≥ H_min.
• alpha.budget.ok: alpha_spent ≤ alpha_budget.
• manifest.ok: non_decreasing(ts) and manifest signature verification passes.

VII. Implementation Bindings I70-14* (Interface Prototypes & Invariants)

• collect_runtime_metrics(sess, window) -> metrics (invariant: time-alignment fields offset/skew/J/u(ts) are present)
• aggregate_sli(metrics, window) -> sli_report (invariant: p95/p99 and convention version included)
• compute_health_score(sli_report, weights) -> H (invariant: 0 ≤ H ≤ 1)
• detect_drift_instrument(ref, cur, methods) -> drift_report ({psi, KL, W1, cusum, ewma})
• evaluate_slo(sli_report, contracts, budget) -> decision (invariant: budget accumulation is monotone)
• apply_runtime_mitigation(sess, decision) -> state' (rate-limit / reconfigure / restart / switch; idempotent)
• emit_sli_manifest(sli_report, decision) -> manifest.instrument.sli (signatures and traceability are mandatory)

VIII. Cross-References

• Timebase & arrival-time harmonization: EFT.WP.Metrology.TimeBase v1.0, Chapters 4, 8–9.
• Synchronization & delay asymmetry: EFT.WP.Metrology.Sync v1.0, Chapters 4–8.
• Cleaning & release freeze: EFT.WP.Methods.Cleaning v1.0, Chapter 10 and Appendix C.
• Drift measures & statistical budgeting: EFT.WP.Methods.CrossStats v1.0, Chapters 7, 14 and Appendix D.

IX. Quality Metrics & Risk Control

1. Suggested SLI roster
   • Availability: uptime_pct, session_open_latency_ms_p99.
   • Performance: cmd_roundtrip_ms_p95/p99, throughput_sps, rho, buffer_util_p95.
   • Data plane: sample_loss_rate, ts_skew_p95, J_p95, u(ts)_p95.
   • Metrology: U_p95, gain_drift_ppm_per_day, offset_drift_units, SNR_drop_db.
   • Quality & compliance: scpi_error_rate, manifest_emit_latency_ms, signature_fail_rate.
2. SLO examples
   uptime_pct ≥ 99.9% / 30d; cmd_roundtrip_ms_p99 ≤ 50; sample_loss_rate ≤ 1e-4; ts_skew_p95 ≤ 1e-6 s; psi ≤ 0.1.
3. Risk control & rollback
   • major: auto rate-limit (lower lambda), shorten windows, increase BAND to stabilize response.
   • critical: switch to redundant links or spare instruments, freeze publication, and trigger manual calibration.
   • After recovery, perform a postmortem and persist root-cause fields: RCA.cause, RCA.fix, RCA.action_items.

Summary
This chapter, via P714-* / S714-* / M70-14 / C70-14* / I70-14*, establishes a closed loop from metric collection and statistical evaluation to alerting, rollback, and manifest persistence for instrument runtime. Core tenets are the stability condition rho < 1, unified timebase tau_mono → ts, balanced focus on distribution drift and false-alarm budgeting, and publication through manifest.instrument.sli as the single trusted source.