[OpenTelemetry] Tracing limitations in middleware

[r34son]

Link to the code that reproduces this issue

https://github.com/r34son/nextjs-handle-request-span-repro

To Reproduce

1. Start Jaeger: pnpm jaeger
2. Run app in second terminal: pnpm dev
3. Open http://localhost:3000 in browser
4. View traces at http://localhost:16686

Current vs. Expected behavior

Current Behavior

1. Trace Fragmentation:

   • Middleware and page executions appear as completely separate traces in Jaeger:

- Example: Request to `/` shows:

 - One trace for middleware with `next.span_type` "BaseServer.handleRequest":

 - Separate trace for page render with `next.span_type` "BaseServer.handleRequest":

2. Edge Runtime Middleware Limitations:
   • Edge middleware shows no OpenTelemetry spans (no custom, and fetch) - see screen above
   • Only Node middleware produces traces (you can repro on node-middleware branch):

Expected Behavior

1. Unified Tracing:

   • Single end-to-end trace for each request

2. Edge Runtime Support:

   • Consistent tracing capabilities across Edge and Node runtimes
   • Basic span creation and instrumentation in Edge middleware

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:39 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6020
  Available memory (MB): 32768
  Available CPU cores: 12
Binaries:
  Node: 22.15.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.9.0
Relevant Packages:
  next: 15.3.2 // Latest available version is detected (15.3.2).
  eslint-config-next: N/A
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Middleware

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

Trying to add custom logging for requests. See https://github.com/r34son/nextjs-handle-request-span-repro/blob/main/access-log-span-processor.ts. But middleware and page rendering generate separate traces in OpenTelemetry, rather than a single unified trace for the complete request lifecycle.

Related:
#67737
#47660
#78926
#51231
#51233
#46543

_NEXT-4676

[r34son]

Hi @dvoytenko - since you've worked on Next.js's OpenTelemetry setup, could you advise on trace separation between middleware and pages?

@icyJoseph Could you help document this OpenTelemetry behavior after the team's discussion? Seeing separate traces for middleware vs page renders (different trace IDs) which breaks request tracking.

[r34son]

I apologize for bothering you, @lforst, but perhaps you could offer some advice if you've encountered a similar issue with Sentry?

[lforst]

i no longer work at sentry but it seems like youre not initializing otel for the edge runtime in instrumentation.ts

[r34son]

i no longer work at sentry but it seems like youre not initializing otel for the edge runtime in instrumentation.ts

added instrumentation using @vercel/otel, that instruments both node and edge runtimes - same behaviour
Branch - https://github.com/r34son/nextjs-handle-request-span-repro/tree/vercel-otel

In build mode it's even 3 traces using @vercel/otel:

[r34son]

Found appropriate test for my case 2451af9#diff-4207142439be777189ec4d699d3017bac5c970a2e58324eca5860c219770b524.
But can't get expected trace with the same setup from test. Maybe it somehow depends on deployment setup?
@dvoytenko It was your commit, could you help a bit?

My repro here https://github.com/r34son/nextjs-handle-request-span-repro/tree/nextjs-test

[r34son]

On branch https://github.com/r34son/nextjs-handle-request-span-repro/tree/propagation
When requesting page with traceparent issue seems to be fixed, there is one trace:

But 2 spans with next.span_type "BaseServer.handleRequest" are confusing, the first with next.bubble: true.

And the second part of issue is still reproduces, that custom trace from middleware and fetch instrumentation are not working

[dilidili]

I found next doesn't handle the middleware.ts properly, remove the middleware.ts then the duplicated traces disappear.

[r34son]

Using NEXT_OTEL_VERBOSE=1 creates each span in new trace, propagation also does not work:

To repro:

Go to https://github.com/r34son/nextjs-handle-request-span-repro/tree/otel-verbose

1. run pnpm local in 1 terminal
2. run pnpm jaeger in 2 terminal
3. run pnpm request in 3 terminal
4. Look at traces at http://localhost:16686

[r34son]

@samcx Could someone from Nextjs team take a look?

[samcx]

@r34son Pinged the team about it!

[dilidili]

Hi @ijjk @samcx , I believe it related to the error throwed by middleware catch, added by

next.js/packages/next/src/server/next-server.ts

Lines 1637 to 1643 in 7d93808

	if (isMiddlewareInvoke) {
	bubblingResult = true
	const err = new Error()
	;(err as any).result = result
	;(err as any).bubble = true
	throw err
	}

Could you clarify why should nextjs throws such error for a expected flow?

After I remove these lines my instrumentation works well with reasonable traces.

Before:

After:

[r34son]

After I remove these lines my instrumentation works well with reasonable traces.

Are there still two separate traces within a single request? But with correct spans after removing bubble error

Btw, here`s the commit where this piece of code was introduced https://github.com/vercel/next.js/pull/54813/files#diff-c49c4767e6ed8627e6e1b8f96b141ee13246153f5e9142e1da03450c8e81e96fR1636