fix(otel): respect OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE for delta temporality

Author: MichaelRuhwedel

README.md

@@ -150,10 +150,18 @@ export OPENCODE_DISABLE_METRICS="cache.count,session.duration,session.token.tota
 
 ```bash
 export OPENCODE_ENABLE_TELEMETRY=1
-export OPENCODE_OTLP_ENDPOINT=https://api.datadoghq.com
+export OPENCODE_OTLP_ENDPOINT=https://otlp.datadoghq.com
 export OPENCODE_OTLP_PROTOCOL=http/protobuf
+export OPENCODE_OTLP_HEADERS="dd-api-key=YOUR_DATADOG_API_KEY"
+
+# Required — Datadog's OTLP intake only accepts delta temporality
+export OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=delta
 ```
 
+> **Note:** The endpoint is `otlp.datadoghq.com` (not `api.datadoghq.com`).
+> Use `otlp.datadoghq.eu` for EU, `otlp.us3.datadoghq.com` for US3, etc.
+> See [Datadog OTLP docs](https://docs.datadoghq.com/opentelemetry/interoperability/otlp_ingest_in_the_agent/) for all regions.
+
 ### Honeycomb example
 
 ```bash

src/otel.ts

@@ -1,7 +1,7 @@
 import { logs } from "@opentelemetry/api-logs"
 import { metrics, trace } from "@opentelemetry/api"
 import { LoggerProvider, BatchLogRecordProcessor } from "@opentelemetry/sdk-logs"
-import { MeterProvider, PeriodicExportingMetricReader } from "@opentelemetry/sdk-metrics"
+import { AggregationTemporality, MeterProvider, PeriodicExportingMetricReader } from "@opentelemetry/sdk-metrics"
 import { BasicTracerProvider, BatchSpanProcessor } from "@opentelemetry/sdk-trace-base"
 import { OTLPLogExporter } from "@opentelemetry/exporter-logs-otlp-grpc"
 import { OTLPMetricExporter } from "@opentelemetry/exporter-metrics-otlp-grpc"
@@ -77,12 +77,18 @@ export function setupOtel(
     ? new OTLPHttpTraceExporter({ url: buildHttpSignalUrl(endpoint, "traces") })
     : new OTLPTraceExporter({ url: endpoint })
 
+  const temporalityPref = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]?.toLowerCase()
+  const preferDelta = temporalityPref === "delta" || temporalityPref === "lowmemory"
+
   const meterProvider = new MeterProvider({
     resource,
     readers: [
       new PeriodicExportingMetricReader({
         exporter: metricExporter,
         exportIntervalMillis: metricsInterval,
+        ...(preferDelta && {
+          temporalitySelector: () => AggregationTemporality.DELTA,
+        }),
       }),
     ],
   })

tests/otel.test.ts

@@ -41,3 +41,42 @@ describe("buildResource", () => {
     expect(resource.attributes["service.name"]).toBe("my-override")
   })
 })
+
+describe("setupOtel temporality", () => {
+  const originalEnv = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]
+  afterEach(() => {
+    if (originalEnv === undefined) {
+      delete process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]
+    } else {
+      process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"] = originalEnv
+    }
+  })
+
+  test("defaults to cumulative when env var is unset", () => {
+    delete process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]
+    const pref = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]?.toLowerCase()
+    const preferDelta = pref === "delta" || pref === "lowmemory"
+    expect(preferDelta).toBe(false)
+  })
+
+  test("selects delta when env var is 'delta'", () => {
+    process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"] = "delta"
+    const pref = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]?.toLowerCase()
+    const preferDelta = pref === "delta" || pref === "lowmemory"
+    expect(preferDelta).toBe(true)
+  })
+
+  test("selects delta when env var is 'lowmemory'", () => {
+    process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"] = "lowmemory"
+    const pref = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]?.toLowerCase()
+    const preferDelta = pref === "delta" || pref === "lowmemory"
+    expect(preferDelta).toBe(true)
+  })
+
+  test("is case-insensitive", () => {
+    process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"] = "Delta"
+    const pref = process.env["OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE"]?.toLowerCase()
+    const preferDelta = pref === "delta" || pref === "lowmemory"
+    expect(preferDelta).toBe(true)
+  })
+})