Duplicate root traces for Next.js

[sbrattla]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/nextjs

SDK Version

10.38.0

Framework Version

18.17.1

Link to Sentry event

No response

Reproduction Example/SDK Setup

No response

Steps to Reproduce

For all requests traced in our Next.js application, we see duplicate root spans. The application seems to start two root spans. One of the spans becomes the "current" span, which child spans attach to. The other span is empty.

We are primarily doing distributed tracing, so the spans in this application starts with sentry request headers.

This is our configuration

1. Trace requests in a Next.js application
   next.config.js

const nextConfig = {
  experimental: {
    instrumentationHook: true,
  },
  typescript: {
    ignoreBuildErrors: true,
  },
  eslint: {
    dirs: ['components', 'pages', 'modules', 'contexts', 'hooks', 'lib'],
  },
  webpack(config) {
    config.module.rules.push({
      test: /\.svg$/i,
      issuer: /\.[jt]sx?$/,
      use: ['@svgr/webpack'],
    })

    return config
  },
}

module.exports = nextConfig

const { withSentryConfig } = require('@sentry/nextjs')

module.exports = withSentryConfig(module.exports, {
  silent: true,
  ignore: [
    '**/*.css',
    '**/*.scss',
    '**/*.less',
    '**/*.png',
    '**/*.jpg',
    '**/*.jpeg',
    '**/*.gif',
    '**/*.svg',
    '**/public/**',
  ],
  include: '.next'
})

** instrumentation-server.ts **

import * as Sentry from '@sentry/nextjs'

Sentry.init({
  dsn: {dsn},
  // Server runtime sampling
  // parentSampled is automatically populated from sentry-trace header sent by browser or edge
  // When browser/edge samples a trace, they send: sentry-trace: <trace-id>-<span-id>-1
  // Next.js Sentry SDK extracts this header and sets parentSampled=true if sampled=1
  tracesSampler: ({ attributes, parentSampled }) => {
    // If parent (browser or edge) sampled the trace, always sample to keep trace complete
    // This ensures browser → edge → server traces remain connected
    if (parentSampled === true) {
      return 1.0
    }

    // Sample 0.1% of other spans (regular application traffic)
    // Note: Uptime bot detection happens at edge (entry point), so we don't check here
    return 0.001
  },
  environment: process.env.ENVIRONMENT || 'production',
  // Add tags to differentiate server-side traces
  beforeSendTransaction(event) {
    // Add runtime tag to identify server-side transactions
    if (event.tags) {
      event.tags.runtime = 'server'
    } else {
      event.tags = { runtime: 'server' }
    }

    // Modify OP for root transaction to indicate server runtime
    if (event.contexts?.trace?.op) {
      event.contexts.trace.op = `server.${event.contexts.trace.op}`
    }

    // Modify OP for each span to indicate server-side
    event.spans =
      event.spans?.map((span) => {
        span.op = `server.${span.op}`
        return span
      }) || []

    return event
  },
  // Configure trace propagation targets for distributed tracing
  // This enables sentry-trace headers to be sent to these domains
  tracePropagationTargets: [
    /^(https?:\/\/)?(content|search|api)\.(test\.)?example\.[a-z]+$/,
    process.env.DRUPAL_BASE_URL
      ? new RegExp(`^${process.env.DRUPAL_BASE_URL.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}`)
      : undefined,
  ].filter((target): target is RegExp => target !== undefined),
})

Expected Result

A single root span for traced requests, with child spans attaching to the single root span.

Actual Result

Duplicate root spans for traced requests. The two root spans have the same name, one is empty and one has child spans.

• The empty span has span_type set to BaseServer.handleRequest
• The span with child spans has origin set to auto.http.nextjs

Additional Context

This is a distributed trace, and the trace starts because the request comes with sentry trace headers.

We've tried setting autoInstrumentMiddleware: false as well as autoInstrumentServerFunctions: false. That had no effect.

Priority

_{React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it.}

[linear]

JS-1648

[RulaKhaled]

Hey @sbrattla, thanks for reaching out. Can you share the Next.js version you’re on and which routing approach are you using?

[sbrattla]

@RulaKhaled I'm using version 14.2.32 of Next, and using Pages Router.