feat: Add materialization, feature freshness, request latency, and push metrics to feature server by ntkathole · Pull Request #6071 · feast-dev/feast

ntkathole

What this PR does / why we need it:

Adds rich Prometheus metrics to the Feast feature server covering areas that previously had no observability:

Request latency histograms with feature_count and feature_view_count labels so operators can correlate latency with request complexity
Materialization tracking — success/failure counters and duration histograms per feature view
Feature freshness gauges — staleness (seconds since last materialization) per feature view, updated via background polling
Online feature retrieval counters — request counts and entity-row-per-request histograms
Push request counters — tracked by push source and mode (online/offline)
CPU and memory gauges — moved from inline code to the shared metrics module
Previously the feature server only had inline CPU/memory monitoring. This PR introduces 10 new metric families covering the full request lifecycle, materialization pipeline, and data freshness.

New metrics

Metric	Type	Labels
`feast_feature_server_request_total`	Counter	`endpoint`, `status`
`feast_feature_server_request_latency_seconds`	Histogram	`endpoint`, `feature_count`, `feature_view_count`
`feast_online_features_request_total`	Counter	—
`feast_online_features_entity_count`	Histogram	—
`feast_push_request_total`	Counter	`push_source`, `mode`
`feast_materialization_total`	Counter	`feature_view`, `status`
`feast_materialization_duration_seconds`	Histogram	`feature_view`
`feast_feature_freshness_seconds`	Gauge	`feature_view`, `project`
`feast_feature_server_cpu_usage`	Gauge	—
`feast_feature_server_memory_usage`	Gauge	—

Configuration

Metrics are fully opt-in with zero overhead when disabled. Enable via CLI or YAML:

feature_server:
  metrics:
    enabled: true
    resource: true          # CPU / memory gauges
    request: true           # endpoint latency & request counters
    online_features: true   # online feature retrieval counters
    push: true              # push request counters
    materialization: true   # materialization counters & duration
    freshness: true         # per-feature-view freshness gauges

Per-category toggles let disable specific metric groups (e.g., keep CPU/memory but skip request latency). All categories default to true. The --metrics CLI flag works without any YAML config.