newt/docs/METRICS_RECOMMENDATIONS.md

Newt Metrics: Recommendations, Gaps, and Roadmap

This document captures the current state of Newt metrics, prioritized fixes, and a pragmatic roadmap for near-term improvements.

1. Current setup (summary)

• Export: Prometheus exposition (default), optional OTLP (gRPC)
• Existing instruments:
  • Sites: newt_site_registrations_total, newt_site_online (0/1), newt_site_last_heartbeat_seconds
  • Tunnel/Traffic: newt_tunnel_sessions, newt_tunnel_bytes_total, newt_tunnel_latency_seconds, newt_tunnel_reconnects_total
  • Connection lifecycle: newt_connection_attempts_total, newt_connection_errors_total
  • Operations: newt_config_reloads_total, newt_restart_count_total, newt_build_info
  • Go runtime: GC, heap, goroutines via runtime instrumentation

2. Main issues addressed now

• Attribute filter (allow-list) extended to include site_id and region in addition to existing keys (tunnel_id, transport, protocol, direction, result, reason, error_type, version, commit).
• site_id and region propagation: site_id is now attached as a metric label across newt_*; region is added as a metric label when set. Both remain resource attributes for consistency with OTEL.
• Label semantics clarified:
  • transport: control-plane mechanism (e.g., websocket, wireguard)
  • protocol: L4 payload type (tcp, udp)
  • newt_tunnel_bytes_total uses protocol and direction, not transport.
• Robustness improvements: removed duplicate clear logic on reconnect; avoided empty site_id by reading NEWT_SITE_ID/NEWT_ID and OTEL_RESOURCE_ATTRIBUTES.

3. Remaining gaps and deviations

• Some call sites still need initiator label on reconnect outcomes (client vs server). This is planned.
• WebSocket and Proxy metrics (connect latency, messages, active connections, buffer/drops, async backlog) are planned additions.
• Config apply duration and cert rotation counters are planned.

4. Roadmap (phased)

• Phase 1 (done in this iteration)
  • Fix attribute filter (site_id, region)
  • Propagate site_id (and optional region) across metrics
  • Correct label semantics (transport vs protocol); fix sessions transport labelling
  • Documentation alignment
• Phase 2 (next)
  • WebSocket: newt_websocket_connect_latency_seconds; newt_websocket_messages_total{direction,msg_type}
  • Proxy: newt_proxy_active_connections, newt_proxy_buffer_bytes, newt_proxy_drops_total, newt_proxy_async_backlog_bytes
  • Reconnect: add initiator label (client/server)
  • Config & PKI: newt_config_apply_seconds{phase,result}; newt_cert_rotation_total{result}

5. Operational guidance

• Do not double scrape: scrape either Newt (/metrics) or the Collector’s Prometheus exporter (not both) to avoid double-counting cumulative counters.
• For high cardinality tunnel_id, consider relabeling or dropping per-tunnel series in Prometheus to control cardinality.
• OTLP troubleshooting: enable TLS via OTEL_EXPORTER_OTLP_CERTIFICATE, use OTEL_EXPORTER_OTLP_HEADERS for auth; verify endpoint reachability.

6. Example alerts/recording rules (suggestions)

• Reconnect spikes:
  • increase(newt_tunnel_reconnects_total[5m]) by (site_id)
• Sustained connection errors:
  • rate(newt_connection_errors_total[5m]) by (site_id,transport,error_type)
• Heartbeat gaps:
  • max_over_time(newt_site_last_heartbeat_seconds[15m]) by (site_id)
• Proxy drops:
  • increase(newt_proxy_drops_total[5m]) by (site_id,protocol)
• WebSocket connect p95 (when added):
  • histogram_quantile(0.95, sum(rate(newt_websocket_connect_latency_seconds_bucket[5m])) by (le,site_id))

7. Collector configuration

• Direct scrape variant requires no attribute promotion since site_id is already a metric label.
• Transform/promote variant remains optional for environments that rely on resource-to-label promotion.

8. Testing

• curl :2112/metrics | grep ^newt_
• Verify presence of site_id across series; region appears when set.
• Ensure disallowed attributes are filtered; allowed (site_id) retained.