160adeb3b8
Task 8 of 10 complete. Exposes read-only scheduler health data including: - Queue depth and distribution by instance type - Dead-letter queue inspection (top 25 tasks with error details) - Circuit breaker states (instance-level) - Staleness scores per instance New API endpoint: GET /api/monitoring/scheduler/health (requires authentication) New snapshot methods: - StalenessTracker.Snapshot() - exports all staleness data - TaskQueue.Snapshot() - queue depth & per-type distribution - TaskQueue.PeekAll() - dead-letter task inspection - circuitBreaker.State() - exports state, failures, retryAt - Monitor.SchedulerHealth() - aggregates all health data Documentation updated with API spec, field descriptions, and usage examples.
153 lines
5.5 KiB
Markdown
153 lines
5.5 KiB
Markdown
# Pulse Adaptive Polling – Phase 2 Summary
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## Executive Summary
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Phase 2 delivers adaptive polling infrastructure that dynamically adjusts monitoring intervals based on instance freshness, error rates, and system load. The scheduler replaces fixed cadences with intelligent priority-based execution, dramatically improving resource efficiency while maintaining data freshness.
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## Completed Tasks (8/10 - 80%)
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### ✅ Task 1: Poll Cycle Metrics
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- 7 new Prometheus metrics (duration, staleness, queue depth, in-flight, errors)
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- Per-instance tracking with histogram/counter/gauge types
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- Integrated into all poll functions (PVE/PBS/PMG)
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- Metrics server on port 9091
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### ✅ Task 2: Adaptive Scheduler Scaffold
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- Pluggable interfaces (StalenessSource, IntervalSelector, TaskEnqueuer)
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- BuildPlan generates ordered task lists with NextRun times
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- FilterDue/DispatchDue for queue management
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- Default no-op implementations for gradual rollout
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### ✅ Task 3: Configuration & Feature Flags
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- `ADAPTIVE_POLLING_ENABLED` feature flag (default: false)
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- Min/max/base interval tuning (5s / 5m / 10s defaults)
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- Environment variable overrides
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- Persisted in system.json
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- Validation logic (min ≤ base ≤ max)
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### ✅ Task 4: Staleness Tracker
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- Per-instance freshness metadata (last success/error/mutation)
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- SHA1 change hash detection
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- Normalized staleness scoring (0-1 scale)
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- Integration with PollMetrics for authoritative timestamps
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- Updates from all poll result handlers
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### ✅ Task 5: Adaptive Interval Logic
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- EMA smoothing (alpha=0.6) to prevent oscillations
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- Staleness-based interpolation (min-max range)
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- Error penalty (0.6x per failure) for faster recovery detection
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- Queue depth stretch (0.1x per task) for backpressure
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- ±5% jitter to avoid thundering herd
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### ✅ Task 6: Priority Queue Execution
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- Min-heap (container/heap) ordered by NextRun + Priority
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- Worker goroutines with WaitNext() blocking
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- Tasks only execute when due (respects adaptive intervals)
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- Automatic rescheduling after execution
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- Upsert semantics prevent duplicates
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### ✅ Task 7: Error Handling & Circuit Breakers
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- Circuit breaker with closed/open/half-open states
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- Trips after 3 consecutive failures
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- Exponential backoff (5s initial, 2x multiplier, 5min max)
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- ±20% jitter on retry delays
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- Dead-letter queue after 5 transient failures
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- Error classification (transient vs permanent)
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### ✅ Task 10: Documentation
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- Architecture guide in `docs/monitoring/ADAPTIVE_POLLING.md`
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- Configuration reference
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- Metrics catalog
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- Operational guidance & troubleshooting
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- Rollout plan (dev → staged → full)
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## Deferred Tasks (2/10 - 20%)
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### ⏭ Task 8: API Surfaces (Future Phase)
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- Scheduler health endpoint
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- Dead-letter queue inspection/management
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- Circuit breaker state visibility
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- UI dashboard integration
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### ⏭ Task 9: Testing Harness (Future Phase)
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- Unit tests for scheduler math
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- Integration tests with mock instances
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- Soak tests for queue stability
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- Regression suite for Phase 1 hardening
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## Key Metrics Delivered
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| Metric | Purpose |
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|--------|---------|
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| `pulse_monitor_poll_total` | Success/error rate tracking |
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| `pulse_monitor_poll_duration_seconds` | Latency per instance |
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| `pulse_monitor_poll_staleness_seconds` | Data freshness indicator |
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| `pulse_monitor_poll_queue_depth` | Backpressure monitoring |
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| `pulse_monitor_poll_inflight` | Concurrency tracking |
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| `pulse_monitor_poll_errors_total` | Error type classification |
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| `pulse_monitor_poll_last_success_timestamp` | Recovery timeline |
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## Technical Achievements
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**Performance:**
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- Adaptive intervals reduce unnecessary polls on idle instances
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- Queue-based execution prevents task pile-up
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- Circuit breakers stop hot loops on failing endpoints
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**Reliability:**
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- Exponential backoff with jitter prevents thundering herd
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- Dead-letter queue isolates persistent failures
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- Transient error retry logic (5 attempts before DLQ)
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**Observability:**
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- 7 Prometheus metrics for complete visibility
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- Structured logging for all state transitions
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- Tamper-evident audit trail (from Phase 1)
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## Deployment Status
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**Current State:** Feature flag disabled by default (`ADAPTIVE_POLLING_ENABLED=false`)
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**Activation Path:**
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1. Enable flag in dev/QA environment
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2. Observe metrics for 24-48 hours
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3. Staged rollout to subset of production clusters
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4. Full activation after validation
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**Rollback:** Set `ADAPTIVE_POLLING_ENABLED=false` to revert to fixed intervals
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## Git Commits
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1. `c048e7b9b` - Tasks 1-3: Metrics + scheduler + config
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2. `8ce93c1df` - Task 4: Staleness tracker
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3. `e8bd79c6c` - Task 5: Adaptive interval logic
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4. `1d6fa9188` - Task 6: Priority queue execution
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5. `7d9aaa406` - Task 7: Circuit breakers & backoff
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6. `[current]` - Task 10: Documentation
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## Phase 2 Success Criteria ✅
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- [x] Metrics pipeline operational
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- [x] Scheduler produces valid task plans
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- [x] Queue respects adaptive intervals
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- [x] Circuit breakers prevent runaway failures
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- [x] Documentation enables ops team rollout
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- [x] Feature flag allows safe activation
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## Known Limitations
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- Dead-letter queue state lost on restart (no persistence yet)
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- Circuit breaker state not exposed via API (Task 8)
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- No automated test coverage (Task 9)
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- Queue depth metric updated per-cycle (not real-time within cycle)
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## Next Steps
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**Immediate (Post-Phase 2):**
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- Deploy to dev environment with flag enabled
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- Configure Grafana dashboards for new metrics
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- Set alerting thresholds (queue depth >50, staleness >60s)
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**Future Phases:**
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- Task 8: REST API for scheduler introspection
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- Task 9: Comprehensive test suite
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- Phase 3: External sentinels and cross-cluster coordination
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