# Instrumentation guide

This document describes the recommended instrumentation contract for this
receiver. It is available at `/instrumentation.md` so frontend and backend
agents can read it before integrating telemetry.

## Shared identity

Use the same values across all signals from one deployed application:

- `service.name`: stable application name, for example `checkout-web`.
- `service.release`: immutable deploy identifier, for example
  `2026.09.18-a1b2c3`.
- `service.environment`: `production`, `staging`, or `development`.

The release must exactly match the source-map upload release.

## Browser frontend

Load the RUM script and initialize it once, before the application starts:

```html
<script src="https://otel.example.com/static/otel-rum.js"></script>
<script>
  const rum = OtelRUM.init({
    serviceName: "checkout-web",
    release: "2026.09.18-a1b2c3",
    environment: "production",
    baseUrl: "https://otel.example.com"
  });
</script>
```

The collector captures uncaught errors, unhandled promise rejections, failed
HTTP requests, breadcrumbs, Web Vitals, and optional trace context. Correlate
frontend requests with backend spans when possible:

```js
fetch("/api/orders", { headers: rum.traceHeaders() });
```

For manually handled errors:

```js
try {
  riskyOperation();
} catch (error) {
  rum.captureException(error, { "feature.name": "checkout" });
}
```

Do not put secrets, tokens, or sensitive customer data in breadcrumbs or
custom attributes.

## React error boundaries

Rendering errors are not reliably caught by global `window.onerror` handlers.
Report them from an error boundary and render a recovery screen:

```tsx
import React from "react";

export class AppErrorBoundary extends React.Component<
  { children: React.ReactNode },
  { error: Error | null }
> {
  state = { error: null as Error | null };

  static getDerivedStateFromError(error: Error) {
    return { error };
  }

  componentDidCatch(error: Error, info: React.ErrorInfo) {
    window.OtelRUM?.last?.captureException(error, {
      "exception.type": "ReactErrorBoundary",
      "react.component_stack": info.componentStack,
    });
  }

  render() {
    if (this.state.error) {
      return <button onClick={() => this.setState({ error: null })}>Retry</button>;
    }
    return this.props.children;
  }
}
```

Use the same pattern in your application, including a user-visible fallback
for individual views and the application root.

## Backend instrumentation

Instrument backend services with an OpenTelemetry SDK or auto-instrumentation
and export OTLP to this receiver:

- OTLP/gRPC: `otel.example.com:4317`
- OTLP/HTTP traces: `https://otel.example.com/v1/traces`
- OTLP/HTTP metrics: `https://otel.example.com/v1/metrics`
- OTLP/HTTP logs: `https://otel.example.com/v1/logs`

Set the resource attributes on every provider/exporter:

```text
service.name=checkout-api
service.release=2026.09.18-a1b2c3
service.environment=production
```

Create spans around inbound requests, database calls, external HTTP calls,
queue operations, and important business operations. Record HTTP status,
route, method, and exception details. Mark failed spans with an error status.
The receiver derives backend issues from error spans and ERROR/FATAL logs.

If HTTP ingest authentication is enabled, provide `OTEL_INGEST_KEY` as the
`X-Otel-Ingest-Key` header or `key` query parameter. Keep that key server-side;
browser clients should not receive it.

For non-interactive agents that need to query protected debug endpoints, use a
separate `OTEL_AGENT_TOKEN` service token. Send it as
`X-Otel-Agent-Token: $OTEL_AGENT_TOKEN`; do not put it in browser code or
telemetry payloads.

## Source maps

Build the frontend with the same immutable release used by RUM. The command
and output directory depend on your build tool; the example below assumes a
standard `dist/` output:

```sh
export RELEASE="2026.09.18-a1b2c3"
VITE_APP_RELEASE="$RELEASE" npm run build
```

After deployment, upload the contents of each generated JavaScript map to the
public multipart endpoint. No repository checkout or upload script is needed.
`source` must match the generated bundle URL/path captured in the browser
stack, while `file=@...` reads the local source-map file contents:

```sh
curl --fail-with-body --silent --show-error \
  -X POST "https://otel.example.com/api/sourcemaps" \
  -F "release=$RELEASE" \
  -F "source=/assets/app-HASH.js" \
  -F "file=@dist/assets/app-HASH.js.map;type=application/json"
```

For example, if the deployed JavaScript is available at
`https://app.example.com/assets/main-abc123.js`, upload its matching map with
`source=/assets/main-abc123.js`. The source-map filename on the build machine
does not need to match the URL, but the `source` field must.

Maps are parsed, written to `OTEL_SOURCEMAP_DIR`, and reloaded on receiver
start. Issue responses include a resolved stack when `service.release` and the
generated bundle path match. Uploaded maps are never returned, but when a map
embeds `sourcesContent` the RUM "JS errors" view shows a few lines of original
source around each mapped frame to signed-in users.

### Requirements checklist

A stack only resolves when every one of these holds. When it does not, check
them in this order:

1. **The build emits maps, with sources embedded.** Enable source maps in the
   bundler (Vite `build.sourcemap: true`, webpack `devtool: "source-map"`).
   Keep `sourcesContent` (the default) or the code view has nothing to show.
2. **The browser reports a release.** Pass the release to `OtelRUM.init({ release })`
   (or `data-release` on the script tag), injected at build time. An event
   with no release, or `dev`, can never match an upload.
3. **The uploaded release is byte-for-byte the same string.** Use one value for
   both the bundle build and the upload (a git short SHA works).
4. **`source` matches the path in the browser stack.** Everything before
   `/assets/` and any `?query` is ignored, so `source=/assets/main-abc123.js`
   matches `https://app.example.com/assets/main-abc123.js`. Content-hashed
   names must match exactly, and chunks each need their own upload.
5. **The map belongs to the deployed bundle.** Upload the maps from the very
   build that produced the deployed files. A second local rebuild can differ
   (dependencies, Node version) and silently mismatch. In Docker, copy the maps
   out of the build stage (`docker build --target <stage>`, then `docker cp`)
   instead of rebuilding. `build.sh` does this.
6. **Every chunk is uploaded.** Loop over all `*.js.map` files and fail the
   deploy when none are found, since an empty loop otherwise succeeds silently.
7. **The receiver keeps its maps.** `OTEL_SOURCEMAP_DIR` must be on persistent
   storage (a PVC in Kubernetes, not `emptyDir`). Maps written to an ephemeral
   directory vanish on restart.
8. **Maps are not published with the site.** Delete `*.map` from the served
   image unless public maps are intended (see below).

### Verifying a deploy

List what the receiver has loaded (requires a signed-in session or token):

```sh
curl -H "Authorization: Bearer $TOKEN" https://otel.example.com/api/sourcemaps
# [{"release":"2026.09.18-a1b2c3","source":"/assets/main-abc123.js"}, ...]
```

Then trigger a real uncaught error from application code, for example a
button that runs `setTimeout(() => { throw new Error("source-map check") })`
(this repository's RUM "JS errors" view has a *Generate test error* button),
and confirm the card shows **Source-mapped** with the original file and line.

Frame status in the stack explorer explains a miss: `no-release` (event has no
release), `no-map` (nothing uploaded for that release and file), or `unmapped`
(a map exists but has no mapping for that position).

The Docker build removes `.map` files from production images by default. For
development or staging, public maps can be enabled for Chrome DevTools:

```sh
PUBLIC_SOURCEMAPS=true ./build.sh
```

Public maps expose application source code and should not be enabled in
production unless that is intentional.

## Verification checklist

1. Trigger a controlled frontend exception.
2. Trigger a controlled backend error span or ERROR log.
3. Confirm both appear under Issues as separate frontend/backend issues.
4. Confirm the issue sample contains the expected release.
5. Confirm a mapped frontend stack shows original file and line information
   (see *Requirements checklist* under Source maps if it does not).
6. Confirm trace IDs connect frontend requests to backend traces where headers
   were propagated.