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feat: add appendix D (observability) #287

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feat: add appendix D (observability) #287

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2d44c6d
feat: add appendix D (observability)
toddbaert Dec 16, 2024
5dc802b
fixup: casing note
toddbaert Dec 16, 2024
23efc79
fixup: links
toddbaert Dec 16, 2024
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3 changes: 3 additions & 0 deletions specification/README.md
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Expand Up @@ -16,8 +16,11 @@ sidebar_position: 0
- [Evaluation Context](./sections/03-evaluation-context.md)
- [Hooks](./sections/04-hooks.md)
- [Events](./sections/05-events.md)
- [Tracking](./sections/06-tracking.md)
- [Appendix A: Included Utilities](./appendix-a-included-utilities.md)
- [Appendix B: Gherkin Suites](./appendix-b-gherkin-suites.md)
- [Appendix C: OFREP](./appendix-c-ofrep.md)
- [Appendix D: Observability](./appendix-d-observability.md)

## Conformance

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51 changes: 51 additions & 0 deletions specification/appendix-d-observability.md
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---
id: appendix-d
title: "Appendix D: Observability"
description: Conventions for OpenFeature telemetry signals
sidebar_position: 5
---

# Appendix D: Observability

This document describes conventions for extracting data from the OpenFeature SDK for use in telemetry signals.
It primarily focuses on providing recommendations for mapping well-known fields in OpenFeature to [OpenTelemetry feature-flag log records](https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-logs/) and other semantic conventions.

## Evaluations

Flag evaluation telemetry comprises data resolved from the provider resolution (evaluation details and flag metadata) as well as metadata about the provider itself.
This is particularly relevant to telemetry-related [hooks](./sections/04-hooks.md).

### Evaluation Details

The following describes how fields on the [evaluation details](types.md#evaluation-details) are mapped to feature flag log records:

| Evaluation Details Field | Log Record Attribute | Notes |
| ------------------------ | --------------------------------------- | ---------------------------------------------------- |
| `flag key` | `feature_flag.key` | See: [flag key](./glossary.md#flag-key) |
| `error code` | `error.type` | See: [error code](./types.md#error-code) |
| `variant` | `feature_flag.variant` | See: [variant](./glossary.md#variant) |
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There's questions about how exactly to represent value (important if provider cannot supply variant):

  • is it represented in the body?
  • can it be of any type?

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is it represented in the body?

Do you mean the body of the log record?

The spec says:

value: If and only if feature flag provider does not supply variant or equivalent concept. 
Otherwise, value should be treated as opt-in.

And the type is undefined there as there is no any type in OTEL.
Recently there was also opened a PR to add the value_type to the event: open-telemetry/semantic-conventions#1689

| `error message` | `feature_flag.evaluation.error.message` | An error message associated with a failed evaluation |
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Should we here also make clear that it is not recommended to not repat error.type here, like it's stated in the otel semcon?

| `reason` | `feature_flag.evaluation.reason` | See: [reason](./types.md#resolution-reason) |

> [!NOTE]
> The `error.type` and `feature_flag.evaluation.reason` enumerations use a lowercase "snake_case" convention (see [OpenTelemetry feature-flag log records](https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-logs/)).
> OpenFeature [error codes](types.md#error-code) and [resolution reasons](./types.md#resolution-reason) should be transformed accordingly by integrations which include this data.

### Flag Metadata

The following describes how keys in [flag metadata](types.md#flag-metadata) are mapped to feature flag log records:

| Flag Metadata Key | Log Record Attribute | Notes |
| ----------------- | ------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `contextId` | `feature_flag.context.id` | The context identifier returned in the flag metadata uniquely identifies the subject of the flag evaluation. If not available, the [targeting key](./glossary.md#targeting-key) should be used. |
| `flagSetId` | `feature_flag.set.id` | A logical identifier for the [flag set](./glossary.md#flag-set). |
| `flagSetVersion` | `feature_flag.version` | A version string (format unspecified) for the [flag set](./glossary.md#flag-set). |

> [!NOTE]
> Keys in flag metadata use the "camelCase" casing convention, while the OpenTelemetry standard uses a namespaced "snake_case" convention.

### Provider Metadata

| Provider Metadata Field | Log Record Attribute | Notes |
| ----------------------- | ---------------------------- | ------------------------------------------------------------------------------------------------ |
| `name` | `feature_flag.provider_name` | The name of the provider as defined in the `provider metadata`, available in the `hook context`. |
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I wonder if we should add a note that it's recommended to keep provider names consistent across provider implementations.

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I don't think it's worth mentioning. I guess providers can decide for themselves if they want the name to be consistent.

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I think so too @toddbaert, it might be interesting for some consumers to see the provider implementations instead of a common name. But I guess @beeme1mr's case is the more common.

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I'm also with @toddbaert regarding a provider name. But I can imagine your point @beeme1mr of having an identifiying property for post processing. Maybe there should also be a provider_id property we could propose in otel?

2 changes: 2 additions & 0 deletions specification/types.md
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Expand Up @@ -58,6 +58,8 @@ A structure which contains a subset of the fields defined in the `evaluation det
- variant (string, optional)
- flag metadata ([flag metadata](#flag-metadata), optional)

#### Resolution Reason

A set of pre-defined reasons is enumerated below:

| Reason | Explanation |
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