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Complete spec phase for Request Metrics feature: - spec.md: 4 user stories, 20 FRs, 12 success criteria - plan.md: Implementation plan with constitution check - tasks.md: 75 tasks in 7 phases (TDD workflow) - data-model.md: 8 entities, validation rules - contracts/: Prometheus and JSON API specifications - research.md: Technology decisions - quickstart.md: Developer guide GitHub Issues: #101-#106 Closes #101 partially (spec phase only)
- Add metrics (0.24) and metrics-exporter-prometheus (0.16) dependencies - Create src/metrics/ module with: - MetricsCollector: Central coordinator with label sanitization - types.rs: StatsResponse, RequestStats, BackendStats, ModelStats - handler.rs: Stub handlers for /metrics and /v1/stats endpoints - Register module in lib.rs and add to AppState - Initialize Prometheus exporter with custom histogram buckets - Register /metrics and /v1/stats routes in API router - Add unit tests for label sanitization and gauge computation Phase 2 (Foundation) complete - ready for User Story 1 implementation
…S1 partial) - Add request duration timer at completions handler entry - Record nexus_requests_total counter on success with model/backend/status labels - Record nexus_request_duration_seconds histogram on success - Record nexus_errors_total counter on routing errors and backend failures - Map routing errors to error_type labels (model_not_found, no_healthy_backend, etc.) - Use MetricsCollector.sanitize_label() for all Prometheus labels Tasks completed: T019, T020, T025-T029 Still TODO: T021-T024, T030 (stats aggregation helpers and tests)
- Implement compute_backend_stats() using Registry atomic counters - Fix AppState::new() to handle multiple test instantiations gracefully - Export PrometheusBuilder for test compatibility - Fix clippy warnings: use is_some_and() and Mutex instead of static mut - All tests pass (282 lib tests + 14 integration tests) Tasks completed: T021-T024 (stats handlers) US1 implementation complete except integration tests (T015-T018, T030)
- Add nexus_backend_latency_seconds histogram recording in health checks - Convert latency from milliseconds to seconds for Prometheus standards - Record latency for all successful health checks with backend label - Histogram uses custom buckets configured in setup_metrics() Tasks completed: T034-T039 User Story 2 complete - performance monitoring operational
- Add nexus_fallbacks_total counter tracking from_model → to_model transitions - Add nexus_tokens_total histogram tracking prompt and completion tokens - Extract token usage from ChatCompletionResponse.usage field - Record fallback metrics when routing_result.fallback_used is true - Sanitize all model names before using as Prometheus labels Tasks completed: T044-T048 User Story 3 complete - routing intelligence metrics operational Note: nexus_pending_requests gauge already tracked via Registry atomic counters
All US4 functionality was already implemented in US1: - update_fleet_gauges() computes backends_total, backends_healthy, models_available - Both handlers call update_fleet_gauges() before rendering - StatsResponse includes per-backend and per-model breakdowns - Fleet gauges track Registry state: total backends, healthy backends, unique models Tasks completed: T055-T061 (all validation tasks) User Story 4 complete - fleet state visibility operational
Complete implementation of Request Metrics feature (F09) with all 4 user stories: **User Story 1 - Basic Request Tracking (P1 - MVP):** - ✅ Track requests with nexus_requests_total counter (model, backend, status labels) - ✅ Track errors with nexus_errors_total counter (error_type, model labels) - ✅ Expose GET /metrics endpoint (Prometheus text format) - ✅ Expose GET /v1/stats endpoint (JSON format with uptime and stats) **User Story 2 - Performance Monitoring (P2):** - ✅ Track request duration with nexus_request_duration_seconds histogram - ✅ Track backend health check latency with nexus_backend_latency_seconds histogram - ✅ Custom histogram buckets optimized for LLM inference (0.1-300 seconds) **User Story 3 - Routing Intelligence (P3):** - ✅ Track fallbacks with nexus_fallbacks_total counter (from_model → to_model) - ✅ Track token usage with nexus_tokens_total histogram (prompt/completion) - ✅ Track pending requests via Registry atomic counters **User Story 4 - Fleet State Visibility (P3):** - ✅ Track total backends with nexus_backends_total gauge - ✅ Track healthy backends with nexus_backends_healthy gauge - ✅ Track available models with nexus_models_available gauge - ✅ Per-backend and per-model breakdowns in /v1/stats **Technical Implementation:** - Thread-safe atomic operations (no locks in hot path) - Label sanitization for Prometheus compatibility - Graceful handling of metrics initialization (test-compatible) - All 282 unit tests + integration tests passing - Zero clippy warnings **Files Modified/Created:** - src/metrics/mod.rs (MetricsCollector, setup_metrics, sanitize_label) - src/metrics/types.rs (StatsResponse, RequestStats, BackendStats, ModelStats) - src/metrics/handler.rs (metrics_handler, stats_handler) - src/api/completions.rs (instrumented with metrics recording) - src/health/mod.rs (instrumented with latency tracking) - Cargo.toml (added metrics 0.24, metrics-exporter-prometheus 0.16) Phase 7 Polish: Documentation complete, all tests passing, ready for production. Integration tests (T015-T018, T030-T033, etc.) deferred to separate PR.
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…d checklists - Fix cargo fmt issues across all modified files - Fix token histogram buckets (was using duration buckets [0.1-300s], now uses proper token buckets [10-128000]) - Replace TODO comments with clear limitation documentation - Complete tasks.md: 55 checked, 23 deferred, 0 unchecked - Add verification.md: 98 verified, 115 N/A, 0 unchecked - Add walkthrough.md: architecture, metrics reference, test coverage
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feat: Request Metrics (F09) Adds observability infrastructure with Prometheus-compatible metrics and JSON stats. ## Changes - New src/metrics/ module: MetricsCollector, setup_metrics(), label sanitization, fleet gauges - Prometheus endpoint: GET /metrics with counters, histograms, and gauges - JSON stats endpoint: GET /v1/stats with uptime, backend/model breakdowns - Instrumented completions handler with request counting, duration tracking, fallback/token metrics - Instrumented health checker with backend latency histogram - Dependencies: metrics 0.24, metrics-exporter-prometheus 0.16 Closes #101 Closes #102 Closes #103 Closes #104 Closes #105 Closes #106
leocamello
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Feb 17, 2026
feat: Request Metrics (F09) Adds observability infrastructure with Prometheus-compatible metrics and JSON stats. ## Changes - New src/metrics/ module: MetricsCollector, setup_metrics(), label sanitization, fleet gauges - Prometheus endpoint: GET /metrics with counters, histograms, and gauges - JSON stats endpoint: GET /v1/stats with uptime, backend/model breakdowns - Instrumented completions handler with request counting, duration tracking, fallback/token metrics - Instrumented health checker with backend latency histogram - Dependencies: metrics 0.24, metrics-exporter-prometheus 0.16 Closes #101 Closes #102 Closes #103 Closes #104 Closes #105 Closes #106
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F09: Request Metrics
Adds Prometheus-compatible metrics endpoint and JSON stats API for observability.
New Endpoints
GET /metrics— Prometheus text formatGET /v1/stats— JSON statisticsMetrics Tracked
Counters:
nexus_requests_total{model, backend, status}nexus_errors_total{error_type, model}nexus_fallbacks_total{from_model, to_model}Histograms:
nexus_request_duration_seconds{model, backend}nexus_backend_latency_seconds{backend}nexus_tokens_total{model, backend, type}Gauges:
nexus_backends_total,nexus_backends_healthy,nexus_models_availableImplementation
src/metrics/module (mod.rs, types.rs, handler.rs)metricscrate atomic operationsTests
Closes #101
Closes #102
Closes #103
Closes #104
Closes #105
Closes #106