Cloudflare Workers Otel Utels

Cloudflare Workers OTel + utels boundary

Two wrappers that compose around a Worker's {fetch, scheduled} handler. Both are no-op pass-throughs unless their env vars are present, so you can run with neither, just one, or both.

withUtelsErrorTracking(withTelemetry(coreHandler))

• withTelemetry — OTLP traces / metrics / logs push when any OTEL_EXPORTER_OTLP_* endpoint is configured. Also wraps every D1 binding with a Proxy that logs event: "d1.slow_query" to wrangler tail, even without OTLP, so the slow-query story works on a fresh deploy.
• withUtelsErrorTracking — pushes one exception event per 5xx response or thrown exception to a utels.dev project. The endpoint, project ID, and ingest token are env-configured.

When to invoke

Use when you're:

• Standing up observability on a new Worker, want OTLP-compatible traces and metrics to any backend (Honeycomb, Grafana Cloud, Tempo, Jaeger collector, …).
• Adding server-side error tracking via utels without changing handler code.
• Investigating a slow query: drop the threshold env var and watch wrangler tail.

What's in here

assets/scripts/telemetry-runtime.ts

The whole runtime, ready to drop into src/. Exports withTelemetry and withUtelsErrorTracking. Bundled by wrangler's esbuild at deploy.

Hot points to customize per-project:

• DEFAULT_SERVICE_NAME — match your worker name.
• EXACT_ROUTES — the set of paths that should NOT be normalized to "unmatched". Add your top-level routes.
• routeForPath(pathname) — extend to collapse :id-style path params. High-card route attributes will explode trace and metric label cardinality if you skip this.

assets/scripts/d1-wrap.ts

The D1 Proxy wrap. Self-contained. Threads SQL templates through prepare → bind chains so the eventual terminal op (first / run / all / raw) records the right statement. Records bindingName, op, sql, durationMs, ok. Strongly typed; safe to use as the entry to type the rest of your telemetry pipeline.

Exports a Recorder = (query: RecordedQuery) => void so you can plug it into something other than the bundled withTelemetry if you have a different aggregation story.

assets/tests/d1-wrap.test.ts and telemetry.test.ts

Reference tests. The d1-wrap test uses mock D1 bindings to validate the Proxy chain + slow-threshold + recorder shape. The telemetry test asserts that 5xx responses + thrown exceptions both produce utels events.

Wiring

// src/worker.ts
import { withTelemetry, withUtelsErrorTracking } from "./telemetry-runtime.ts";

const coreHandler = { fetch(req, env, ctx) { /* ... */ } };
const fetchHandler = withUtelsErrorTracking(withTelemetry(coreHandler));

export default {
  fetch: fetchHandler.fetch,
};

// wrangler.jsonc
{
  "vars": {
    "OTEL_SERVICE_NAME": "my-app",
    "OTEL_SERVICE_VERSION": "0.1.0",
    "DEPLOY_ENV": "production",
    // Optional utels
    "UTELS_ENDPOINT": "https://utels.dev/__utels?v=1",
    "UTELS_PROJECT_ID": "my-app-prod",
    "UTELS_RELEASE": "0.1.0"
  }
}

# Optional OTLP. Set any of these to enable trace/metric/log push.
pnpm exec dotenvx set OTEL_EXPORTER_OTLP_ENDPOINT https://api.honeycomb.io -f .env.cloudflare
pnpm exec dotenvx set OTEL_EXPORTER_OTLP_HEADERS "x-honeycomb-team=<key>" -f .env.cloudflare

# Optional utels ingest token (wrangler secret, not committed)
pnpm exec wrangler secret put UTELS_INGEST_TOKEN

Disable individually with OTEL_SDK_DISABLED=true or UTELS_DISABLED=true.

Slow-query independence

withTelemetry ALWAYS wraps D1 bindings with the Proxy. Even when OTLP is unconfigured, every query whose duration crosses APP_D1_SLOW_THRESHOLD_MS (default 250ms) gets logged as a structured console.warn that wrangler tail picks up. This is the cheapest possible "is my query slow?" loop — works on day-one of a new deploy.

References

• references/otlp-payload-shapes.md — the exact shape of the traces/metrics/logs JSON the runtime emits, with notes on what each OTLP backend cares about.
• references/utels-event-shape.md — the exception event schema utels expects.

Source

The runtime is identical to mizchi/cloudflare-starterkit-mbt and mizchi/mnemo.