Add support for backend telemetry (tracing & metrics)

This uses the opentelemetry SDK to provide support for traces and two
simple metrics (a conversations count and a messages count).

The telemetry entrypoint is built separately (unfortunately it does not
seem like there is a method for doing this in one build as sveltekit
overrides rollupOptions).

As written the metrics may be too high cardinality for some use cases
(as they are keyed per user), but these attributes can always be dropped
in a collector.

Dockerfile

@@ -19,7 +19,7 @@ RUN --mount=type=cache,target=/app/.npm \
 COPY --link --chown=1000 . .
 
 RUN --mount=type=secret,id=DOTENV_LOCAL,dst=.env.local \
-    npm run build
+        npm run build && npm run build -- --config vite.telemetry.config.ts
 
 FROM node:20-slim
 
@@ -29,4 +29,4 @@ COPY --from=builder-production /app/node_modules /app/node_modules
 COPY --link --chown=1000 package.json /app/package.json
 COPY --from=builder /app/build /app/build
 
-CMD pm2 start /app/build/index.js -i $CPU_CORES --no-daemon
+CMD pm2 start /app/build/index.js --node-args="--require /app/build/telemetry.cjs" -i $CPU_CORES --no-daemon

package.json

@@ -5,7 +5,7 @@
 	"packageManager": "[email protected]",
 	"scripts": {
 		"dev": "vite dev",
-		"build": "vite build",
+		"build": "bash scripts/clean-opentelemetry.sh && vite build",
 		"preview": "vite preview",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
 		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
@@ -53,6 +53,12 @@
 		"@huggingface/hub": "^0.5.1",
 		"@huggingface/inference": "^2.6.3",
 		"@iconify-json/bi": "^1.1.21",
+		"@opentelemetry/api": "^1.8.0",
+		"@opentelemetry/auto-instrumentations-node": "^0.44.0",
+		"@opentelemetry/exporter-metrics-otlp-proto": "^0.50.0",
+		"@opentelemetry/sdk-metrics": "^1.23.0",
+		"@opentelemetry/sdk-node": "^0.50.0",
+		"@opentelemetry/sdk-trace-node": "^1.23.0",
 		"@resvg/resvg-js": "^2.6.0",
 		"@xenova/transformers": "^2.16.1",
 		"autoprefixer": "^10.4.14",

src/routes/conversation/+server.ts

@@ -10,6 +10,7 @@ import { defaultEmbeddingModel } from "$lib/server/embeddingModels";
 import { v4 } from "uuid";
 import { authCondition } from "$lib/server/auth";
 import { usageLimits } from "$lib/server/usageLimits";
+import { metrics } from "@opentelemetry/api";
 
 export const POST: RequestHandler = async ({ locals, request }) => {
 	const body = await request.text();
@@ -111,6 +112,15 @@ export const POST: RequestHandler = async ({ locals, request }) => {
 		...(values.fromShare ? { meta: { fromShareId: values.fromShare } } : {}),
 	});
 
+	const meter = metrics.getMeter("chat-ui");
+	const counter = meter.createCounter("chat-ui.conversations.count", {
+		description: "The number of conversations created",
+	});
+	counter.add(1, {
+		"chat-ui.model": values.model,
+		"user.email": locals.user?.email || undefined,
+	});
+
 	return new Response(
 		JSON.stringify({
 			conversationId: res.insertedId.toString(),

src/routes/conversation/[id]/+server.ts

@@ -23,6 +23,7 @@ import { addSibling } from "$lib/utils/tree/addSibling.js";
 import { preprocessMessages } from "$lib/server/preprocessMessages.js";
 import { usageLimits } from "$lib/server/usageLimits";
 import { isURLLocal } from "$lib/server/isURLLocal.js";
+import { metrics } from "@opentelemetry/api";
 
 export async function POST({ request, locals, params, getClientAddress }) {
 	const id = z.string().parse(params.id);
@@ -243,6 +244,15 @@ export async function POST({ request, locals, params, getClientAddress }) {
 			messageId
 		);
 
+		const meter = metrics.getMeter("chat-ui");
+		const counter = meter.createCounter("chat-ui.conversations.messages.count", {
+			description: "The number of user messages created",
+		});
+		counter.add(1, {
+			"chat-ui.model": "values.model",
+			"user.email": locals.user?.email || undefined,
+		});
+
 		messageToWriteToId = addChildren(
 			conv,
 			{

src/telemetry.ts

@@ -0,0 +1,77 @@
+// This file is built outside of sveltekit and cannot import from the rest of the application
+// or special imports like $env/dynamic/private.
+import { NodeSDK } from "@opentelemetry/sdk-node";
+import { getNodeAutoInstrumentations } from "@opentelemetry/auto-instrumentations-node";
+import { PeriodicExportingMetricReader } from "@opentelemetry/sdk-metrics";
+import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-proto";
+import { OTLPMetricExporter } from "@opentelemetry/exporter-metrics-otlp-proto";
+import { SEMRESATTRS_SERVICE_NAME } from "@opentelemetry/semantic-conventions";
+import { AlwaysOnSampler } from "@opentelemetry/sdk-trace-base";
+import { Resource } from "@opentelemetry/resources";
+
+const TRACE_URL =
+	process.env.OTEL_EXPORTER_OTLP_ENDPOINT + "/v1/traces" || "http://localhost:4318/v1/traces";
+const METRICS_URL =
+	process.env.OTEL_EXPORTER_OTLP_ENDPOINT + "/v1/metrics" || "http://localhost:4318/v1/metrics";
+const SERVICE_NAME = process.env.OTEL_SERVICE_NAME || "huggingface/chat-ui";
+
+const exporter = new OTLPTraceExporter({
+	url: TRACE_URL,
+	headers: {},
+});
+
+const otelNodeSdk = new NodeSDK({
+	autoDetectResources: true,
+	serviceName: SERVICE_NAME,
+	traceExporter: exporter,
+	metricReader: new PeriodicExportingMetricReader({
+		exporter: new OTLPMetricExporter({
+			url: METRICS_URL,
+			headers: {},
+		}),
+	}),
+	sampler: new AlwaysOnSampler(),
+	resource: new Resource({
+		[SEMRESATTRS_SERVICE_NAME]: SERVICE_NAME,
+	}),
+	instrumentations: [
+		getNodeAutoInstrumentations({
+			"@opentelemetry/instrumentation-http": {
+				ignoreIncomingRequestHook: (request) => {
+					// Don't trace static asset requests
+					if (
+						request.url?.endsWith(".js") ||
+						request.url?.endsWith(".svg") ||
+						request.url?.endsWith(".css")
+					) {
+						return false;
+					}
+					return true;
+				},
+			},
+		}),
+	],
+});
+
+export class Telemetry {
+	private static instance: Telemetry;
+	private initialized = false;
+
+	private constructor() {}
+
+	public static getInstance(): Telemetry {
+		if (!Telemetry.instance) {
+			Telemetry.instance = new Telemetry();
+		}
+		return Telemetry.instance;
+	}
+
+	public start() {
+		if (!this.initialized) {
+			this.initialized = true;
+			otelNodeSdk.start();
+		}
+	}
+}
+
+Telemetry.getInstance().start();

vite.telemetry.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig } from "vite";
+
+export default defineConfig({
+	build: {
+		emptyOutDir: false,
+		ssr: true,
+		target: "node18",
+		outDir: "build",
+		rollupOptions: {
+			input: {
+				telemetry: "src/telemetry.ts",
+			},
+		},
+		lib: {
+			formats: ["cjs"],
+			entry: "src/telemetry.ts",
+		},
+	},
+});