feat: Add trace when evaluating feature flags by kylejuliandev · Pull Request #755 · open-feature/dotnet-sdk

kylejuliandev · 2026-05-07T18:49:22Z

This PR

Add trace when evaluating feature flags. This is different from the TraceEnricherHook which enriches the current span or trace with an event, instead this more closely follows the semantic conventions: https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-events/. Also add OpenTelemetry logging to the sample application and ensure traces are always sampled.

Success tracwe

Error trace

Related Issues

Fixes #595
Fixes #541

Notes

Follow-up Tasks

How to test

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

codecov · 2026-05-07T18:52:15Z

Codecov Report

❌ Patch coverage is 98.21429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.61%. Comparing base (5623a0f) to head (06fc54b).

Files with missing lines	Patch %	Lines
src/OpenFeature/OpenFeatureActivitySource.cs	97.29%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #755      +/-   ##
==========================================
+ Coverage   93.52%   93.61%   +0.08%     
==========================================
  Files          69       70       +1     
  Lines        2981     3037      +56     
  Branches      355      374      +19     
==========================================
+ Hits         2788     2843      +55     
  Misses        135      135              
- Partials       58       59       +1

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gemini-code-assist

Code Review

This pull request implements OpenTelemetry tracing for feature flag evaluations in the OpenFeature client, including the addition of an activity source and corresponding unit tests. The review feedback highlights several discrepancies with OpenTelemetry Semantic Conventions, suggesting the use of standard attribute names (e.g., 'feature_flag.provider_name', 'feature_flag.evaluation_reason', 'feature_flag.evaluation_value', 'feature_flag.variant') and recommending that span statuses be explicitly set to 'Error' when failures occur to improve telemetry accuracy.

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

askpt

LGTM! I expect this change to be mentioned in a README since the consumer might need to add extra configuration to remove or add these traces.

cc: @beeme1mr, @open-feature/technical-steering-committee, @WeihanLi, @arttonoyan

WeihanLi · 2026-05-13T11:56:53Z

        var provider = providerInfo.Item2;

+        var activity = OpenFeatureActivitySource.StartActivity("feature_flag.evaluation");
+        activity?.SetTag("feature_flag.key", flagKey);


for the SetTag/SetStatus, think we could add tags in one place and add tags only when IsAllDataRequested

https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.activity.isalldatarequested?view=net-10.0

Fixed in 6e943fa - this was a great spot! It helps avoid allocations in high performance scenarios

I wonder if we should add feature_flag.provider.name in all instances or only when IsAllDataRequested is true

WeihanLi · 2026-05-13T12:02:36Z

maybe we want to deprecate the TraceEnricherHook related code also?

WeihanLi · 2026-05-13T12:07:31Z

+        var providerMetadata = provider.GetMetadata();
+        if (providerMetadata != null)
+        {
+            activity?.SetTag("feature_flag.provider.name", providerMetadata.Name);


Would we like to keep these tagName/activityName to be constants in a separated place?

Fixed in 6e943fa - moved the tag names (apart from error.type) to the OpenFeatureActivitySource class

WeihanLi · 2026-05-13T12:09:29Z

    .ConfigureResource(resource => resource.AddService("openfeature-aspnetcore-sample"))
    .WithTracing(tracing => tracing
        .AddAspNetCoreInstrumentation()
+        .SetSampler(new AlwaysOnSampler())


Maybe we should add AddSource("OpenFeature") to collect OpenFeature activity?

Added trace source in 3b8eac5

* Ensure OpenFeature traces are recorded in sample app * Ensure ActivitySource is disposed of Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

* Add check on IsAllDataRequested to save on allocations on the activity span Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

kylejuliandev · 2026-05-14T19:22:47Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces OpenTelemetry instrumentation to the OpenFeature .NET SDK by adding a new OpenFeatureActivitySource and integrating activity tracking into the OpenFeatureClient evaluation logic. The changes include mapping evaluation results and errors to standard semantic conventions and adding comprehensive tests. Review feedback suggests aligning specific attribute names with OpenTelemetry standards (specifically provider_name and variant), normalizing reason strings to lowercase, and removing a redundant Dispose() call on an activity already managed by a using statement.

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

WeihanLi · 2026-05-19T07:33:37Z

+                activity?.SetStatus(ActivityStatusCode.Error);
+
+                if (activity?.IsAllDataRequested == true)
+                {
+                    activity.AddTag("error.type", OpenFeatureActivitySource.GetFlagEvaluationErrorDescription(evaluation.ErrorType));
+                    activity.SetTag(OpenFeatureActivitySource.FeatureFlagErrorMessageName, evaluation.ErrorMessage);
+                }


seems there's some duplication, maybe we could add one method to avoid duplicates

private static void AttachActivityTags(Activity? activity, FlagEvaluationDetails<T>? evaluation, Exception? exception = null) { if (activity is null) return; if (elaluation?.ErrorType != ErrorType.None) activity.SetStatus(ActivityStatusCode.Error); if (activity.IsAllDataRequested != true) return; if (elaluation is null) { // ... return; } activity.SetTag(OpenFeatureActivitySource.FeatureFlagReasonName, OpenFeatureActivitySource.GetFlagEvaluationReasonDescription(evaluation.Reason)); if (elaluation?.ErrorType == ErrorType.None) { activity.SetTag(OpenFeatureActivitySource.FeatureFlagValueName, evaluation.Value); activity.SetTag(OpenFeatureActivitySource.FeatureFlagVariantName, evaluation.Variant); } else { activity.AddTag("error.type", OpenFeatureActivitySource.GetFlagEvaluationErrorDescription(evaluation.ErrorType)); activity.SetTag(OpenFeatureActivitySource.FeatureFlagErrorMessageName, evaluation.ErrorMessage); } }

Actually with all IsAllDataRequested I wonder if makes sense to have an internal extension method to have the AddTag and SetTag. Like AddTagIfRequested or SetTagIfRequested. It would make the code cleaner IMO.

What do you think @WeihanLi and @kylejuliandev?

I think I prefer the extension method approach. It keeps activity enrichment close to the code but simplifies the repeated if IsAllDataRequested checks

think it's more cleaner to introduce extension method for AddTagIfRequested/SetTagIfRequested, but it may cause some duplicated not null and IsAllDataRequested checks, maybe it should be avoid for a hotpath.
While maybe we could evaluate this further if someone complains about this.

askpt · 2026-05-19T15:09:22Z

maybe we want to deprecate the TraceEnricherHook related code also?

Not at this point. Until OTEL formally deprecates events in traces, I would keep this Hook enabled since they have different behaviour.

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

askpt

Added two minor comments.

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

kylejuliandev added 3 commits May 6, 2026 23:15

Add OpenTelemetry log exporting and ensure traces reliably sample

3b609d9

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Add code to start activity and initial unit tests

703798f

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Add additional unit tests and ensure tags are added

73ee185

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

kylejuliandev requested a review from a team as a code owner May 7, 2026 18:49

gemini-code-assist Bot reviewed May 7, 2026

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kylejuliandev added 4 commits May 7, 2026 20:12

Fix build issue

24ea6b6

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Address gemini code review comments

3dce87e

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Add tests to improve code coverage of OpenFeatureActivitySource

a6b8ec3

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Set activity kind to internal

7e99375

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

askpt reviewed May 13, 2026

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Comment thread src/OpenFeature/OpenFeatureActivitySource.cs Outdated

Comment thread src/OpenFeature/OpenFeatureClient.cs Outdated

WeihanLi reviewed May 13, 2026

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Comment thread src/OpenFeature/OpenFeatureClient.cs Outdated

WeihanLi reviewed May 13, 2026

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kylejuliandev added 2 commits May 14, 2026 20:04

Ensure major.minor.patch version is included in trace

3b8eac5

* Ensure OpenFeature traces are recorded in sample app * Ensure ActivitySource is disposed of Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Move tag keys to string constants in separate class

6e943fa

* Add check on IsAllDataRequested to save on allocations on the activity span Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

gemini-code-assist Bot reviewed May 14, 2026

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Comment thread src/OpenFeature/OpenFeatureActivitySource.cs

Comment thread src/OpenFeature/OpenFeatureActivitySource.cs

Comment thread src/OpenFeature/OpenFeatureActivitySource.cs

Comment thread src/OpenFeature/OpenFeatureClient.cs Outdated

Remove duplicate activity disposal

6d64f4f

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

WeihanLi reviewed May 19, 2026

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askpt requested review from arttonoyan, beeme1mr and toddbaert May 19, 2026 15:15

kylejuliandev added 2 commits May 20, 2026 18:36

Add internal extension method for adding tags to activities

21c9a1c

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

Merge branch 'main' into kylej/improve-tracing

23d0839

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

askpt reviewed May 20, 2026

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Comment thread src/OpenFeature/OpenFeatureActivitySource.cs Outdated

Comment thread src/OpenFeature/OpenFeatureClient.cs Outdated

Remove null check on Activity and create constant for error.type

06fc54b

Signed-off-by: Kyle Julian <38759683+kylejuliandev@users.noreply.github.com>

askpt approved these changes May 21, 2026

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benjiro approved these changes May 23, 2026

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askpt mentioned this pull request Jun 2, 2026

fix: Change registration to use the Isolated API instead of global singleton #760

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