feat(infra): add OTel auto-instrumentations across all services

NestJS 6 services use getNodeAutoInstrumentations().

Python 2 services use FastAPIInstrumentor. Go 2 services use otelgin.

services/teacher-bff/src/config/env.ts

@@ -5,6 +5,7 @@ const envSchema = z.object({
   IamServiceUrl: z.string().url().default("http://localhost:3002"),
   ClassesServiceUrl: z.string().url().default("http://localhost:3001"),
   CoreEduServiceUrl: z.string().url().default("http://localhost:3004"),
+  OTEL_EXPORTER_OTLP_ENDPOINT: z.string().url().optional(),
   LOG_LEVEL: z.string().default("info"),
   NODE_ENV: z.string().default("development"),
 });

services/teacher-bff/src/main.ts

@@ -1,11 +1,13 @@
-import 'reflect-metadata';
-import { NestFactory } from '@nestjs/core';
-import { AppModule } from './app.module.js';
-import { env } from './config/env.js';
+import "reflect-metadata";
+import { NestFactory } from "@nestjs/core";
+import { AppModule } from "./app.module.js";
+import { env } from "./config/env.js";
+import { initTracer, shutdownTracer } from "./shared/observability/tracer.js";
 
 async function bootstrap(): Promise<void> {
+  initTracer();
   const app = await NestFactory.create(AppModule, {
-    logger: ['log', 'error', 'warn'],
+    logger: ["log", "error", "warn"],
   });
 
   app.enableShutdownHooks();
@@ -13,12 +15,13 @@ async function bootstrap(): Promise<void> {
   await app.listen(env.PORT);
   console.log(`Teacher BFF started on port ${env.PORT}`);
 
-  process.on('SIGTERM', async () => {
+  process.on("SIGTERM", async () => {
     await app.close();
+    await shutdownTracer();
   });
 }
 
 bootstrap().catch((err: unknown) => {
-  console.error('Failed to start Teacher BFF', err);
+  console.error("Failed to start Teacher BFF", err);
   process.exit(1);
 });

services/teacher-bff/src/shared/observability/tracer.ts

@@ -0,0 +1,27 @@
+import { getNodeAutoInstrumentations } from "@opentelemetry/auto-instrumentations-node";
+import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-http";
+import { NodeSDK } from "@opentelemetry/sdk-node";
+import { env } from "../../config/env.js";
+
+let sdk: NodeSDK | null = null;
+
+export function initTracer(): void {
+  if (!env.OTEL_EXPORTER_OTLP_ENDPOINT) return;
+
+  sdk = new NodeSDK({
+    serviceName: "teacher-bff",
+    traceExporter: new OTLPTraceExporter({
+      url: `${env.OTEL_EXPORTER_OTLP_ENDPOINT}/v1/traces`,
+    }),
+    instrumentations: [getNodeAutoInstrumentations()],
+  });
+
+  sdk.start();
+  console.log("Tracer initialized with auto-instrumentations");
+}
+
+export async function shutdownTracer(): Promise<void> {
+  if (sdk) {
+    await sdk.shutdown();
+  }
+}