OpenTelemetry

Overview

Export evaluation events as OpenTelemetry spans.

The OpenTelemetry exporter converts each feature evaluation into an OpenTelemetry span. Each span contains attributes with non-sensitive evaluation details such as the flag key, the evaluated variation, the evaluation context key and optional metadata.

This exporter is a streaming exporter (not a bulk exporter) and will create one span per feature evaluation.

info

The exporter does not configure an OpenTelemetry SDK/tracer provider for you. You must initialize and configure OpenTelemetry (OTLP/exporter, resource, sampler, etc.) in your application so that spans are exported to your tracing backend.

Behaviour

• Export mode: streaming — the exporter implements IsBulk() returning false.
• For each evaluation it creates a span named feature_flag.evaluate and attaches attributes:
  • feature_flag.key, feature_flag.user_key, feature_flag.context_kind, feature_flag.variation, feature_flag.default, feature_flag.version, feature_flag.source
  • feature_flag.value (JSON stringified when available)
  • feature_flag.metadata.<key> for each metadata entry
• If the default value was used, the span status will be set to an error code to signal fallback usage.

Configure the GO Module

To use the exporter in your application with the GO Module, provide an instance of the exporter in the ffclient.Config DataExporter.Exporter field. Optionally override the tracer name with TracerName.

example.go

import (
    "context"

    "github.com/thomaspoignant/go-feature-flag/exporter/opentelemetryexporter"
    "github.com/thomaspoignant/go-feature-flag/ffclient"
)

// ... initialize your OpenTelemetry tracer provider here (OTLP, resource, etc.) ...

cfg := ffclient.Config{
    // ... other config ...
    DataExporter: ffclient.DataExporter{
        Exporter: &opentelemetryexporter.Exporter{
            TracerName: "app-featureflags", // optional, default: "go-feature-flag"
        },
    },
}

_ = ffclient.Init(cfg)
defer ffclient.Close()

Field	Mandatory	Description
TracerName		Optional: override the OpenTelemetry tracer name. Default is go-feature-flag.

Configure the Relay Proxy

The Relay Proxy supports a per-flagset OpenTelemetry exporter (kind: opentelemetry). This exporter creates one span per evaluation using the configured tracerName and the process-wide OpenTelemetry TracerProvider. The relay proxy itself must have OpenTelemetry SDK/exporter configured so spans are sent to your collector — you can configure this using the proxy top-level otel section or environment variables (see relay proxy observability docs).

Example (relay proxy config):

goff-proxy.yaml

server:
  mode: http
  port: 1031

# Configure the relay proxy OpenTelemetry SDK/exporter (process-level)
otel:
  exporter:
    otlp:
      endpoint: http://otel-collector:4317
      protocol: grpc
  resource:
    attributes:
      service.name: relay-proxy

# A flagset that exports evaluation events as OpenTelemetry spans
flagsets:
  - name: default
    retriever:
      kind: file
      path: examples/retriever_file/flags.goff.yaml
    exporters:
      - kind: opentelemetry
        tracerName: go-feature-flag

Notes:

• otel (top-level) config controls the OpenTelemetry SDK and the OTLP exporter used by the proxy process. Ensure it points to your collector (OTLP endpoint) or export configuration is provided via environment variables.
• The per-flagset exporter only accepts tracerName currently; the exporter re-uses the process global TracerProvider. If you need a per-exporter OTLP endpoint or different SDK settings, we can extend the exporter configuration to include those fields in a follow-up change.

Examples and notes

• Make sure an OpenTelemetry TracerProvider is configured before evaluations happen; otherwise spans will not be exported (they will be no-ops).
• The exporter sets the span timestamp using the original event creation time when available.
• Because values are JSON-marshalled, very large values may increase span payload size; prefer sending only non-sensitive, compact metadata.