[DOCS] OTel-aligned ADK telemetry config (OTEL_* env vars, OTLP metrics, configurable keys)

[inference-gateway-maintainer]

What changed

The A2A ADK telemetry configuration was aligned with OpenTelemetry conventions in inference-gateway/adk#228 (closes inference-gateway/adk#227). This introduces new public config env vars that should be documented on the user-facing docs site.

New / changed configuration

Standard OpenTelemetry variables (read without a prefix; take precedence over the deprecated TELEMETRY_* aliases):

• OTEL_METRICS_EXPORTER - prometheus (default) | otlp | none
• OTEL_TRACES_EXPORTER - otlp | none (default)
• OTEL_EXPORTER_OTLP_ENDPOINT - OTLP base URL shared by traces and metrics
• OTEL_EXPORTER_OTLP_PROTOCOL - http/protobuf (default) | grpc
• OTEL_EXPORTER_PROMETHEUS_HOST / OTEL_EXPORTER_PROMETHEUS_PORT

Deprecated aliases (still honored): TELEMETRY_METRICS_HOST/PORT, TELEMETRY_TRACE_ENABLE, TELEMETRY_TRACE_ENDPOINT, TELEMETRY_TRACE_HEADERS.

Configurable attribute / baggage keys (default to OTel semantic conventions):

• TELEMETRY_ATTR_SESSION_ID_KEY - default session.id
• TELEMETRY_ATTR_TOOL_CALL_ID_KEY - default gen_ai.tool.call.id

New capability: OTLP metrics push (periodic reader) alongside the existing Prometheus pull endpoint. The Prometheus pull server only runs when metrics resolve to the prometheus exporter.

Affected pages

• Telemetry / observability configuration reference for the ADK.
• Any env-var matrix that lists TELEMETRY_* variables.

Source

• PR: feat: OTel-aligned telemetry config and OTLP metrics push adk#228
• In-repo docs already updated: docs/telemetry.md and README.md in inference-gateway/adk.

[edenreich]

@claude Is this still relevant? check with the original project if it's relevant.

[inference-gateway-maintainer]

Claude finished @edenreich's task in 9m 22s —— View job • docs/issue-398-20260715-0128 • [Create PR ➔](https://github.com/inference-gateway/docs/compare/main...docs/issue-398-20260715-0128?quick_pull=1&title=Issue%20%23398%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%23398%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

---

Yes - still relevant. Docs updated.

• Read the current ADK / telemetry docs in this repo
• Checked the original project (inference-gateway/adk)
• Confirmed relevance
• Updated the ADK Telemetry section in adk.md
• Lint / format check
• Opened PR

What I checked upstream

• inference-gateway/adk#228 ("feat: OTel-aligned telemetry config and OTLP metrics push") is MERGED (2026-07-14), and issue docs: document run-duration-ms output and Duration footer field #227 is CLOSED.
• The upstream docs/telemetry.md documents the full new surface, which matches this ticket exactly.

Why it was still relevant

The docs site's ADK Telemetry section (adk.md) still described only the legacy vars (TELEMETRY_ENABLE, TELEMETRY_METRICS_PORT, TELEMETRY_METRICS_HOST, TELEMETRY_ENDPOINT) - no OTEL_* selectors, no OTLP metrics push, no configurable attribute keys. The recent commit #399 only touched observability.md (the Gateway's spec.telemetry), a different surface, so the ADK page was never updated.

What I changed

Rewrote the ## Telemetry section of adk.md to document:

• OTEL_METRICS_EXPORTER (prometheus|otlp|none), OTEL_TRACES_EXPORTER (otlp|none), OTEL_EXPORTER_OTLP_ENDPOINT, OTEL_EXPORTER_OTLP_PROTOCOL (http/protobuf|grpc), OTEL_EXPORTER_PROMETHEUS_HOST/PORT
• OTLP metrics push (periodic reader) + Prometheus pull, and that the pull server only runs when metrics resolve to prometheus
• TELEMETRY_ATTR_SESSION_ID_KEY (default session.id) and TELEMETRY_ATTR_TOOL_CALL_ID_KEY (default gen_ai.tool.call.id)
• The deprecated TELEMETRY_* aliases (still honored; OTEL_* wins) + link to the upstream guide

format:check and markdownlint pass.

Scope note: I limited the change to the Go ADK (adk.md), the surface adk#228 covers. typescript-adk.md and rust-adk.md are separate upstream repos with their own telemetry stories and weren't part of that PR, so I left them untouched.

PR: #400 - docs: align ADK telemetry config with OpenTelemetry

--- | branch docs/issue-398-20260715-0128