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Rewrite FastAPI instrumentor middleware stack to be failsafe #3664

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Rewrite FastAPI instrumentor middleware stack to be failsafe #3664

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outergod
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@outergod outergod commented Jul 30, 2025 •
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Description

Change the way the FastAPI instrumentor deals with the FastAPI middleware stack so that exception handling code doesn't get executed twice, but still has a valid OTEL context available. At the same time, make sure instrumentor hooks failures cannot crash the service itself.

Fixes #3642
Fixes #3637

Type of change

  • Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Using the MRE in the linked issue, and added unit tests.

Does This PR Require a Core Repo Change?

  • No.

Checklist:

  • Followed the style guidelines of this project
  • Changelogs have been updated
  • Unit tests have been added
  • Documentation has been updated (not needed)

@outergod outergod changed the title Fix/gh 3642 fastapi exceptions Rewrite FastAPI instrumentor middleware stack to be failsafe Jul 30, 2025
@outergod outergod requested a review from a team as a code owner July 30, 2025 11:00
This was referenced Aug 5, 2025
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alexmojaki
alexmojaki suggested changes Aug 15, 2025
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alexmojaki
alexmojaki reviewed Aug 18, 2025
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alexmojaki
alexmojaki approved these changes Aug 19, 2025
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Looks solid, thank you so much!

@outergod
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Thank you for the thorough review and the persistence @alexmojaki!
Do you have any suggestions how to find a maintainer to sponsor the PR? Should I ask on the CNCF Slack?

@alexmojaki
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@xrmx @emdneto @codefromthecrypt @lzchen please review? This relates to #3012 which you reviewed previously. Also cc @Kludex @adriangb

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Successfully merging this pull request may close these issues.

FastAPI instrumentation: errors in hooks not handled properly FastAPI instrumentor stops recording exception event starting v0.55b0
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@outergod @alexmojaki