feat(server): add OpenTelemetry instrumentation

apps/server/src/app.ts

@@ -3,6 +3,7 @@ import { Hono } from "hono";
 import { cors } from "hono/cors";
 
 import exportRoute from "./routes/export";
+import metricsRoute from "./routes/metrics";
 import probeModelsRoute from "./routes/probe-models";
 import workflowRoute from "./routes/workflow";
 
@@ -15,7 +16,8 @@ const app = new Hono()
   .get("/health", (c) => c.json({ status: "ok" }))
   .route("/api/workflow", workflowRoute)
   .route("/api/export", exportRoute)
-  .route("/api/probe-models", probeModelsRoute);
+  .route("/api/probe-models", probeModelsRoute)
+  .route("/api/metrics", metricsRoute);
 
 logger.info("Server app initialized");
 

apps/server/src/index.ts

@@ -1,6 +1,20 @@
+import { initOTel } from "@app/logger/otel";
+
 import app, { AppRoutes } from "./app";
 
-const IDLE_TIMEOUT_IN_SECONDS = 0; // ! No timeout – we must set per-request timeout
+const IDLE_TIMEOUT_IN_SECONDS = 0; // ! No timeout – we must set per-request timeout
+
+const { shutdown: shutdownOTel } = initOTel({
+  serviceName: "calca-server",
+  otlpEndpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT ?? "http://localhost:4318/v1/traces",
+  metricsEndpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT
+    ? process.env.OTEL_EXPORTER_OTLP_ENDPOINT.replace("/v1/traces", "/v1/metrics")
+    : undefined,
+  enabled: process.env.OTEL_ENABLED !== "false",
+});
+
+process.on("SIGTERM", shutdownOTel);
+process.on("SIGINT", shutdownOTel);
 
 Bun.serve({
   fetch: app.fetch,

apps/server/src/routes/metrics.ts

@@ -0,0 +1,25 @@
+import { tokenAggregator } from "@calca/pipeline";
+import { type Context, Hono } from "hono";
+
+export const metricsRouter = new Hono();
+
+metricsRouter.get("/", (c: Context) => {
+  const u = tokenAggregator.get();
+  // Prometheus text format
+  const body = [
+    `# HELP calca_input_tokens Total input tokens used`,
+    `# TYPE calca_input_tokens counter`,
+    `calca_input_tokens ${u.inputTokens}`,
+    `# HELP calca_output_tokens Total output tokens used`,
+    `# TYPE calca_output_tokens counter`,
+    `calca_output_tokens ${u.outputTokens}`,
+    `# HELP calca_total_tokens Total tokens used`,
+    `# TYPE calca_total_tokens counter`,
+    `calca_total_tokens ${u.totalTokens}`,
+    "",
+  ].join("\n");
+
+  return c.text(body, 200, { "Content-Type": "text/plain; charset=utf-8" });
+});
+
+export default metricsRouter;

otel-local.yaml

@@ -0,0 +1,20 @@
+receivers:
+  otlp:
+    protocols:
+      http:
+        endpoint: 0.0.0.0:4318
+
+exporters:
+  debug:
+    verbosity: detailed
+  prometheus:
+    endpoint: 0.0.0.0:4319
+
+service:
+  pipelines:
+    traces:
+      receivers: [otlp]
+      exporters: [debug]
+    metrics:
+      receivers: [otlp]
+      exporters: [prometheus]

package.json

@@ -46,6 +46,11 @@
     "bun": ">=1.0.0"
   },
   "packageManager": "bun@1.2.10",
+  "overrides": {
+    "@opentelemetry/sdk-metrics": "1.29.0",
+    "@opentelemetry/resources": "1.29.0",
+    "@opentelemetry/sdk-trace-node": "1.29.0"
+  },
   "dependencies": {
     "@ai-sdk/provider-utils": "^4.0.23",
     "@inlang/paraglide-js-adapter-vite": "^1.2.40",

packages/logger/package.json

@@ -5,7 +5,8 @@
   "license": "AGPL-3.0",
   "type": "module",
   "exports": {
-    ".": "./src/index.ts"
+    ".": "./src/index.ts",
+    "./otel": "./src/otel.ts"
   },
   "scripts": {
     "typecheck": "bunx tsc --noEmit",
@@ -18,7 +19,17 @@
   },
   "dependencies": {
     "@logtape/logtape": "^2.0.5",
-    "@logtape/pretty": "^2.0.5"
+    "@logtape/pretty": "^2.0.5",
+    "@opentelemetry/api": "^1.9.0",
+    "@opentelemetry/exporter-metrics-otlp-http": "^0.56.0",
+    "@opentelemetry/exporter-trace-otlp-http": "^0.56.0",
+    "@opentelemetry/instrumentation-fetch": "^0.56.0",
+    "@opentelemetry/instrumentation-http": "^0.56.0",
+    "@opentelemetry/resources": "^1.29.0",
+    "@opentelemetry/sdk-metrics": "^1.29.0",
+    "@opentelemetry/sdk-node": "^0.56.0",
+    "@opentelemetry/sdk-trace-node": "^1.29.0",
+    "@opentelemetry/semantic-conventions": "^1.29.0"
   },
   "devDependencies": {
     "@types/node": "^25.6.0",

packages/logger/src/otel.ts

@@ -0,0 +1,53 @@
+// Initializes OTel SDK with OTLP HTTP exporter.
+// Call once at server startup (apps/server/src/index.ts or similar).
+// Returns a shutdown function to flush traces on exit.
+
+import { OTLPMetricExporter } from "@opentelemetry/exporter-metrics-otlp-http";
+import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";
+import { FetchInstrumentation } from "@opentelemetry/instrumentation-fetch";
+import { HttpInstrumentation } from "@opentelemetry/instrumentation-http";
+import { Resource } from "@opentelemetry/resources";
+import { PeriodicExportingMetricReader } from "@opentelemetry/sdk-metrics";
+import { NodeSDK } from "@opentelemetry/sdk-node";
+import {
+  SEMRESATTRS_SERVICE_NAME,
+  SEMRESATTRS_SERVICE_VERSION,
+} from "@opentelemetry/semantic-conventions";
+
+export interface OTelConfig {
+  serviceName: string;
+  serviceVersion?: string;
+  otlpEndpoint: string; // e.g. "http://localhost:4318/v1/traces"
+  metricsEndpoint?: string; // e.g. "http://localhost:4318/v1/metrics"
+  enabled?: boolean;
+}
+
+export function initOTel(config: OTelConfig): { shutdown: () => Promise<void> } {
+  if (!config.enabled) {
+    return { shutdown: async () => {} };
+  }
+
+  const resource = new Resource({
+    [SEMRESATTRS_SERVICE_NAME]: config.serviceName,
+    [SEMRESATTRS_SERVICE_VERSION]: config.serviceVersion ?? "0.0.0",
+  });
+
+  const sdk = new NodeSDK({
+    resource,
+    traceExporter: new OTLPTraceExporter({ url: config.otlpEndpoint }),
+    metricReader: config.metricsEndpoint
+      ? new PeriodicExportingMetricReader({
+          exporter: new OTLPMetricExporter({ url: config.metricsEndpoint }),
+          exportIntervalMillis: 10_000,
+        })
+      : undefined,
+    instrumentations: [new HttpInstrumentation(), new FetchInstrumentation()],
+  });
+
+  sdk.start();
+  return {
+    shutdown: async () => {
+      await sdk.shutdown();
+    },
+  };
+}

packages/logger/tsconfig.json

@@ -2,7 +2,7 @@
   "extends": "../../packages/config/tsconfig/base.json",
   "compilerOptions": {
     "rootDir": "./src",
-    "types": ["node-dom-types"]
+    "types": ["node", "node-dom-types"]
   },
   "include": ["src/**/*.ts"]
 }