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Merge branch 'pratik/otel-phase9-metric-gap-fill' into pratik/otel-phase10-workload-validation

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# Conflicts:
#	.gitignore
#	OpenTelemetryPlan/06-implementation-phases.md
#	docs/telemetry-runbook.md
This commit is contained in:
Pratik Mankawde
2026-08-04 16:11:56 +01:00
parent d662d96d6a 3860c93db2
commit 3ee76bc4ee
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OpenTelemetryPlan/06-implementation-phases.md
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@@ -466,186 +466,6 @@ beast::insight::Collector (abstract interface — unchanged)
#### Data Flow (after Phase 7)
```mermaid
graph LR
subgraph xrpldNode["xrpld Node"]
A["Trace Macros<br/>XRPL_TRACE_SPAN"]
B["beast::insight<br/>OTelCollector"]
end
subgraph collector["OTel Collector :4317 / :4318"]
direction TB
R1["OTLP Receiver<br/>:4317 gRPC | :4318 HTTP"]
BP["Batch Processor"]
SM["SpanMetrics Connector"]
R1 --> BP
BP --> SM
end
subgraph backends["Trace Backends"]
D["Tempo"]
end
subgraph metrics["Metrics Stack"]
E["Prometheus :9090<br/>scrapes :8889<br/>span-derived + native OTel metrics"]
end
subgraph viz["Visualization"]
F["Grafana :3000"]
end
A -->|"OTLP/HTTP :4318<br/>(traces)"| R1
B -->|"OTLP/HTTP :4318<br/>(metrics)"| R1
BP -->|"OTLP/gRPC"| D
SM -->|"RED metrics"| E
R1 -->|"system metrics<br/>(native OTLP)"| E
E --> F
D --> F
style A fill:#4a90d9,color:#fff,stroke:#2a6db5
style B fill:#d9534f,color:#fff,stroke:#b52d2d
style R1 fill:#5cb85c,color:#fff,stroke:#3d8b3d
style BP fill:#449d44,color:#fff,stroke:#2d6e2d
style SM fill:#449d44,color:#fff,stroke:#2d6e2d
style D fill:#f0ad4e,color:#000,stroke:#c78c2e
style E fill:#f0ad4e,color:#000,stroke:#c78c2e
style F fill:#5bc0de,color:#000,stroke:#3aa8c1
style xrpldNode fill:#1a2633,color:#ccc,stroke:#4a90d9
style collector fill:#1a3320,color:#ccc,stroke:#5cb85c
style backends fill:#332a1a,color:#ccc,stroke:#f0ad4e
style metrics fill:#332a1a,color:#ccc,stroke:#f0ad4e
style viz fill:#1a2d33,color:#ccc,stroke:#5bc0de
```
**Key change**: StatsD receiver removed from collector. Both traces and metrics enter via OTLP receiver on the same port.
#### Configuration
```ini
# [insight] section — new "otel" server option
[insight]
server=otel # NEW: uses OTel OTLP metrics exporter
prefix=xrpld # metric name prefix (preserved)
# Endpoint and auth inherited from [telemetry] section:
[telemetry]
enabled=1
endpoint=http://localhost:4318/v1/traces
```
The `OTelCollector` reads the OTLP endpoint from `[telemetry]` config (replacing `/v1/traces` with `/v1/metrics` for the metrics exporter). No additional config keys needed.
**Backward compatibility**: `server=statsd` continues to work exactly as before.
See [Phase7_taskList.md](./Phase7_taskList.md) for detailed per-task breakdown.
### Instrument Type Mapping
| beast::insight | OTel Metrics SDK | Rationale |
| ---------------------- | -------------------------------- | ---------------------------------------------------------------- |
| Counter (int64, `\|c`) | `Counter<int64_t>` | Direct 1:1 mapping |
| Gauge (uint64, `\|g`) | `ObservableGauge<uint64_t>` | Async callback matches existing Hook polling pattern |
| Meter (uint64, `\|m`) | `Counter<uint64_t>` | Fixes non-standard wire format; meters are semantically counters |
| Event (ms, `\|ms`) | `Histogram<double>` | Duration distributions with explicit bucket boundaries |
| Hook (1s callback) | `PeriodicMetricReader` alignment | Same 1s collection interval |
### Tasks
| Task | Description |
| ---- | ------------------------------------------------------------------------- |
| 7.1 | Add OTel Metrics SDK to build deps (conan/cmake) |
| 7.2 | Implement `OTelCollector` class (~400-500 lines) |
| 7.3 | Update `CollectorManager` — add `server=otel` |
| 7.4 | Update OTel Collector YAML (add metrics pipeline, remove StatsD receiver) |
| 7.5 | Preserve metric names in Prometheus (naming strategy) |
| 7.6 | Update Grafana dashboards (if names change) |
| 7.7 | Update integration tests |
| 7.8 | Update documentation (runbook, reference docs) |
### Exit Criteria
- [ ] All 255+ metrics visible in Prometheus via OTLP pipeline (no StatsD receiver)
- [ ] `server=otel` is the default in development docker-compose
- [ ] `server=statsd` still works as a fallback
- [ ] Existing Grafana dashboards display data correctly
- [ ] Integration test passes with OTLP-only metrics pipeline
- [ ] No performance regression vs StatsD baseline (< 1% CPU overhead)
- [ ] Deferred Task 6.1 (`|m` wire format) no longer relevant
---
## 6.8 Phase 7: Native OTel Metrics Migration (Weeks 11-12)
**Objective**: Replace `StatsDCollector` with a native OpenTelemetry Metrics SDK implementation behind the existing `beast::insight::Collector` interface, eliminating the StatsD UDP dependency and unifying traces and metrics into a single OTLP pipeline.
### Motivation: Why Migrate from StatsD to Native OTel Metrics
The Phase 6 StatsD bridge was a pragmatic first step, but it retains inherent limitations that native OTel export resolves.
#### What We Gain
1. **Unified telemetry pipeline** — Traces and metrics export via the same OTLP/HTTP endpoint to the same OTel Collector. One protocol, one endpoint, one config. Eliminates the split-brain architecture of "OTLP for traces, StatsD UDP for metrics."
2. **Eliminates StatsD UDP limitations** — StatsD is fire-and-forget over UDP with no delivery guarantees, no backpressure, 1472-byte MTU packet fragmentation, and text-based encoding overhead. OTLP uses HTTP/gRPC with retries, binary protobuf encoding, and connection-level flow control.
3. **Fixes the `|m` wire format issue** — The `StatsDMeterImpl` uses non-standard `|m` StatsD type that the OTel StatsD receiver silently drops. Native OTel counters eliminate this problem entirely (Phase 6 Task 6.1 — DEFERRED becomes resolved).
4. **Richer metric semantics** — OTel Metrics SDK supports explicit histogram bucket boundaries, exemplars (linking metrics to traces), resource attributes, and metric views. StatsD has no concept of these.
5. **Removes infrastructure dependency** — No more StatsD receiver needed in the OTel Collector. One less receiver to configure, monitor, and debug. Simplifies the collector YAML.
6. **Metric-to-trace correlation** — OTel metrics and traces share the same resource attributes (service.name, service.instance.id). Grafana can link from a metric spike directly to the traces that caused it — impossible with StatsD-sourced metrics.
7. **Production-grade export** — OTel's `PeriodicMetricReader` provides configurable export intervals, batch sizes, timeout handling, and graceful shutdown — all built into the SDK rather than hand-rolled in `StatsDCollectorImp`.
#### What We Lose
1. **StatsD ecosystem compatibility** — Operators using external StatsD-compatible backends (Datadog Agent, Graphite, Telegraph) will need to switch to OTLP-compatible backends or keep `server=statsd` as a fallback.
2. **Simplicity of UDP** — StatsD's UDP fire-and-forget model is dead simple and has zero connection management. OTLP/HTTP requires a TCP connection, TLS negotiation (in production), and retry logic. The OTel SDK handles this, but it's more moving parts.
3. **Slightly higher memory** — OTel SDK maintains internal aggregation state for metrics before export. StatsD just formats and sends strings. Expected overhead: ~1-2 MB additional for metric state.
4. **Dependency on OTel C++ Metrics SDK stability** — The Metrics SDK is GA since 1.0 and on version 1.18.0, but it's less battle-tested than the tracing SDK in the C++ ecosystem.
#### Decision
The gains (unified pipeline, delivery guarantees, metric-trace correlation, simpler collector config) significantly outweigh the losses. `StatsDCollector` is retained as a fallback via `server=statsd` for operators who need StatsD ecosystem compatibility during the transition period.
### Architecture
#### Class Hierarchy (after Phase 7)
```
beast::insight::Collector (abstract interface — unchanged)
|
+-- StatsDCollector (existing — retained as fallback, deprecated)
| +-- StatsDCounterImpl -> StatsD |c over UDP
| +-- StatsDGaugeImpl -> StatsD |g over UDP
| +-- StatsDMeterImpl -> StatsD |m over UDP (non-standard)
| +-- StatsDEventImpl -> StatsD |ms over UDP
| +-- StatsDHookImpl -> 1s periodic callback
|
+-- NullCollector (existing — unchanged, used when disabled)
| +-- NullCounterImpl -> no-op
| +-- NullGaugeImpl -> no-op
| +-- NullMeterImpl -> no-op
| +-- NullEventImpl -> no-op
| +-- NullHookImpl -> no-op
|
+-- OTelCollector (NEW — Phase 7)
+-- OTelCounterImpl -> otel::Counter<int64_t>
+-- OTelGaugeImpl -> otel::ObservableGauge<uint64_t>
+-- OTelMeterImpl -> otel::Counter<uint64_t>
+-- OTelEventImpl -> otel::Histogram<double>
+-- OTelHookImpl -> 1s periodic callback (same pattern)
```
#### Data Flow (after Phase 7)
```mermaid
graph LR
subgraph xrpldNode["xrpld Node"]