monitoring-observability

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• SKILL.md

SKILL.md (first lines)

# Monitoring & Observability

## Overview

This skill covers the three pillars of observability -- traces, metrics, and logs -- along with alerting, dashboards, and health check patterns. It focuses on OpenTelemetry as the vendor-neutral standard, structured logging for queryability, distributed tracing for microservice debugging, and SLO-based alerting to reduce noise.

Use this skill when instrumenting applications for production visibility, setting up monitoring infrastructure, debugging distributed systems, configuring alerts that matter, or building dashboards for operations and product teams.

---

## Core Principles

1. **Instrument at boundaries** - Trace every external call (HTTP, database, queue, cache). Internal function tracing adds noise; boundary tracing reveals system behavior.
2. **Structured over unstructured** - Every log entry must be JSON with correlation IDs, service name, and context. Unstructured logs are unsearchable at scale.
3. **Alert on symptoms, not causes** - Alert when users are affected (error rate, latency SLO breach), not when a specific server metric spikes. Symptom-based alerting reduces noise by 80%.
4. **Correlate across signals** - A trace ID should connect logs, traces, and metrics for a single request. Without correlation, debugging distributed issues requires guesswork.
5. **Budget your error rate** - Define SLOs (99.9% availability = 43 minutes/month downtime budget). Alert when the error budget burn rate is too fast, not on individual errors.

---

## Key Patterns

### Pattern 1: OpenTelemetry Instrumentation (Node.js)

**When to use:** Any production Node.js service that needs traces, metrics, and log correlation.

**Implementation:**

```typescript
// tracing.ts - Must be imported BEFORE any other module
import { NodeSDK } from "@opentelemetry/sdk-node";
import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";
import { OTLPMetricExporter } from "@opentelemetry/exporter-metrics-otlp-http";
import { PeriodicExportingMetricReader } from "@opentelemetry/sdk-metrics";
import { getNodeAutoInstrumentations } from "@opentelemetry/auto-instrumentations-node";
import { Resource } from "@opentelemetry/resources";
import {
  ATTR_SERVICE_NAME,
  ATTR_SERVICE_VERSION,
  ATTR_DEPLOYMENT_ENVIRONMENT,
} from "@opentelemetry/semantic-conventions";

const sdk = new NodeSDK({
  resource: new Resource({
    [ATTR_SERVICE_NAME]: process.env.SERVICE_NAME ?? "my-service",
    [ATTR_SERVICE_VERSION]: process.env.SERVICE_VERSION ?? "0.0.0",
    [ATTR_DEPLOYMENT_ENVIRONMENT]: process.env.NODE_ENV ?? "development",
  }),
  traceExporter: new OTLPTraceExporter({
    url: process.env.OTEL_EXPORTER_OTLP_ENDPOINT ?? "http://localhost:4318/v1/traces",
  }),
  metricReader: new PeriodicExportingMetricReader({
    exporter: new OTLPMetricExporter({
      url: process.env.OTEL_EXPORTER_OTLP_ENDPOINT ?? "http://localhost:4318/v1/metrics",
    }),
    exportIntervalMillis: 30_000,
  }),
  instrumentations: [
    getNodeAutoInstrumentations({
      // Disable noisy fs instrumentation
      "@opentelemetry/instrumentation-fs": { enabled: false },
      // Configure HTTP to capture request/response headers
      "@opentelemetry/instrumentation-http": {
        requestHook: (span, request) => {
          span.setAttribute("http.request.header.x-request-id",
            request.headers?.["x-request-id"] ?? "unknown"
          );
        },
      },
    }),
  ],
});

sdk.start();

process.on("SIGTERM", () => {
  sdk.shutdown().then(() => process.exit(0));
});
```

```typescript
// Custom span creation for business logic
import { trace, SpanStatusCode, context } from "@opentelemetry/api";

const tracer = trace.getTracer("order-service");

async function processOrder(orderId: string): Promise<Order> {
  return tracer.startActiveSpan("process_order", async (span) => {
    try {
      span.setAttribute("order.id", orderId);

      const order = await tracer.startActiveSpan("fetch_order", async (fetchSpan) => {
        const result = await db.orders.findUnique({ where: { id: orderId } });
        fetchSpan.setAttribute("order.total", result?.total ?? 0);
        fetchSpan.end();
        return result;
      });

      if (!order) {
        span.setStatus({ code: SpanStatusCode.ERROR, message: "Order not found" });
        throw new OrderNotFoundError(orderId);
      }

      await tracer.startActiveSpan("charge_payment", async (paymentSpan) => {
        paymentSpan.setAttribute("payment.amount", order.total);
        await paymentService.charge(order);
        paymentSpan.end();
      });

      span.setStatus({ code: SpanStatusCode.OK });
      return order;
    } catch (error) {
      span.setStatus({ code: SpanStatusCode.ERROR, message: String(error) });
      span.recordException(error as Error);
      throw error;
    } finally {
      span.end();
    }
  });

From travisjneuman/.claude, MIT.

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