# Datadog Event Forwarding

## Objective

Ship the app's metrics, logs, and deploy events to Datadog with tags that stay consistent.

A single outbound telemetry path to Datadog, with an agreed tag set, batching, sampling, and redaction applied before send.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Decide first what is worth sending — the handful of metrics, log streams, and deployment markers someone would actually look at during an incident — and route all of them through one outbound path rather than scattering calls across the codebase.
2. Fix a small, mandatory tag set applied to everything: service, environment, version, and where the app is multi-tenant, an opaque tenant identifier. Set them from the same configuration the deploy uses, so a dashboard filter works the same across metrics, logs, and traces.
3. Treat every tag value as a cardinality decision. User identifiers, request identifiers, URLs with embedded values, and raw error messages must not become tag values; put them in the log body or trace attributes where they belong.
4. Buffer and batch outbound telemetry through the app's existing background processing, with a bounded queue that drops oldest-first when it fills. Telemetry must never be sent inline on the request path or hold a user request open.
5. Redact before the payload is constructed, not after: credentials, tokens, authorisation headers, payment details, and personal data must never reach the buffer. Keep the API credential in server-side configuration and never in a browser bundle.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- High-cardinality tags are the standard way this integration becomes expensive overnight, because each distinct value creates a new time series. Enforce an allowed tag key list and reject values that look unbounded.
- Payloads also have size limits. Truncate long log bodies and stack traces at a defined length with a marker, rather than letting an oversized payload be rejected wholesale and the event lost.
- Inconsistent service, environment, version, or tenant metadata makes correlation impossible — a metric tagged one way and a log tagged another cannot be joined. Derive all four from one place and assert their presence before send.
- Secrets and personal data leak in through log lines and exception messages more often than through deliberate fields. Redact at the source and default to excluding unknown structured fields.
- A noisy loop or a failing endpoint will flood the pipeline and the bill. Sample repetitive events at a defined rate and aggregate counters locally before shipping them rather than sending one call per occurrence.
- When Datadog is unreachable, the app must degrade to local logging and continue serving users. Do not retry synchronously, do not grow the buffer without limit, and do not let a telemetry failure surface as a user-facing error.
- Backoff must be applied on rate limiting and on server errors, with jitter, or every instance will retry in lockstep and prolong the outage.
- Losing telemetry is acceptable; losing user requests is not. Make the dropped-event count itself an observable number so silent loss is visible.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] All outbound telemetry leaves through a single path with a mandatory service, environment, version, and tenant tag set.
- [ ] Tag keys are restricted to an allowed list and unbounded values are rejected before send.
- [ ] No credential or personal data is present in forwarded metrics, logs, or events, verified against a captured payload.
- [ ] Sending is batched off the request path and never delays or fails a user request.
- [ ] Noisy events are sampled or aggregated, and oversized payloads are truncated rather than dropped whole.
- [ ] A provider outage falls back to local logging with a bounded buffer, backoff with jitter, and a visible dropped-event count.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.