OpenTelemetry in Vercel Functions

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When to use this

• You want spans from your own code: database queries, calls to other services, AI model and tool calls.
• You want those spans to continue into services outside Vercel.
• Your functions produce a lot of telemetry per request, where the drain’s $0.50 per GB adds up.

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Bronto OTLP endpoint

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Next.js (and other frameworks) with @vercel/otel

1. Install the package:
   npm install @vercel/otel @opentelemetry/api
   
2. Register it in instrumentation.ts in the project root (or in src/):
   instrumentation.ts

   import { registerOTel } from "@vercel/otel";
   
   export function register() {
     registerOTel({
       serviceName: "my-app",
       attributes: { "service.namespace": "my-team" },
       instrumentationConfig: {
         // Services outside Vercel that should continue the trace.
         fetch: { propagateContextUrls: ["https://api.example.com"] },
       },
     });
   }
   
3. Set the exporter in the project’s environment variables (Settings → Environment Variables):
   OTEL_EXPORTER_OTLP_ENDPOINT=https://ingestion.eu.bronto.io
   OTEL_EXPORTER_OTLP_HEADERS=x-bronto-api-key=<YOUR_API_KEY>
   
   Values are percent-decoded (W3C Baggage format), so encode a comma, semicolon or % inside a value. An = at the end of an API key can stay as it is.
4. Redeploy. Spans appear in Explore Traces under the service name you set.

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With a trace drain on the same project

• Through the trace drain: remove the direct exporter (or don’t set OTEL_EXPORTER_OTLP_*). Your spans are billed as drain volume at $0.50 per GB.
• Direct export: keep OTEL_EXPORTER_OTLP_* and don’t add a trace drain. The export costs function time instead of drain fees (see below), but Vercel’s infrastructure spans then don’t reach Bronto.

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Agents built with eve

npm install @opentelemetry/exporter-trace-otlp-proto@0.223

import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-proto";
import { otelIntegration } from "eve/instrumentation/otel";

// Reads OTEL_EXPORTER_OTLP_ENDPOINT and OTEL_EXPORTER_OTLP_HEADERS
export default otelIntegration({ traceExporter: new OTLPTraceExporter() });

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What exporting costs

• Exporting in waitUntil (or after() in Next.js) keeps the delay away from your users, but not from the bill.
• Work in waitUntil shares the function’s timeout. If the function times out, unsent spans are lost.
• Vercel traces the export itself: the trace drain carries a vercel.serverless-runtime span for every outgoing POST …/v1/traces call (2,325 in 20 minutes in the test project).

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Example