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Fix for FASTAPI unable to record AppService URL (Issue #3654) #3670

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Fix for FASTAPI unable to record AppService URL (Issue #3654) #3670

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rads-1996
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Description

Fixes #3654

Type of change

Please delete options that are not relevant.

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • This change requires a documentation update

How Has This Been Tested?

  • Added tests in both asgi and fastapi instrumentation to ensure the host value is fetched.

Does This PR Require a Core Repo Change?

  • Yes. - Link to PR:
  • No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

  • Followed the style guidelines of this project
  • Changelogs have been updated
  • Unit tests have been added
  • Documentation has been updated

@rads-1996 rads-1996 requested a review from a team as a code owner August 1, 2025 15:07
@rads-1996 rads-1996 marked this pull request as draft August 1, 2025 15:07
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Before Change -

Screenshot 2025-08-01 143500

After Change -

Screenshot 2025-08-01 143511

@rads-1996 rads-1996 marked this pull request as ready for review August 1, 2025 23:16
@xrmx xrmx moved this to Ready for review in @xrmx's Python PR digest Aug 4, 2025
xrmx
xrmx reviewed Aug 4, 2025
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@rads-1996 rads-1996 mentioned this pull request Aug 4, 2025
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@rads-1996 rads-1996 requested a review from xrmx August 14, 2025 19:57
emdneto
emdneto reviewed Aug 15, 2025
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@emdneto emdneto left a comment •
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Left some comments. One thought though is we don't even need the HTTP_URL attribute for server spans even for old semantic convention, but I believe it's another discussion.

http.url is usually not readily available on the server side but would have to be assembled in a cumbersome and sometimes lossy process from other information

@Kludex
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Kludex commented Aug 15, 2025 •
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I think the current implementation is correct. I don't think the instrumentation should trust the "Host" header.

@rads-1996
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rads-1996 commented Aug 15, 2025 •
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I think the current implementation is correct. I don't think the instrumentation should trust the "Host" header.

But then the IP address appearing in the url field instead of the actual application url address is not very desirable. @Kludex Do you think there is another way to overcome this issue.

@rads-1996 rads-1996 requested a review from Kludex August 18, 2025 21:52
@rads-1996 rads-1996 requested a review from emdneto August 21, 2025 21:00
@jeremydvoss
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Long needed fix. Thanks @rads-1996! Fastapi and asgi should behave like the other instrumentations and use the url when available.

emdneto
emdneto approved these changes Sep 4, 2025
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I agree host header is 100% safe, but approving because it looks good to me and is consistent with the WSGI instrumentation. Also, is the way semantic conventions recommends to get the hostname https://opentelemetry.io/docs/specs/semconv/http/http-spans/#setting-serveraddress-and-serverport-attributes. btw, for new semconv we are not recording it #2698

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@jeremydvoss jeremydvoss jeremydvoss approved these changes

@emdneto emdneto emdneto approved these changes

@xrmx xrmx Awaiting requested review from xrmx

@Kludex Kludex Awaiting requested review from Kludex

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FastAPI can fail to record App Service URL
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@rads-1996 @Kludex @jeremydvoss @xrmx @emdneto