opentelemetry-instrumentation-tornado: reduce cardinality of span names and metrics attributes

[xrmx]

Description

This PR fixes two cardinality issues for the tornado instrumentation:

• in the span name, where we are now using a low-cardinality version of the request path
• in the metrics attributes for stable http semantic conventions. This changes the attributes of some of the metrics dropping out of spec url.query, url.path in favor of in-spec http.route. For older semantic conventions this is not possible since http.target is high cardinality by definition.

Since Tornado does not offer us any helper to get the templated name of a route from the handler we need to introduce a basic reimplementation of its routing algorithm. We then reuse a tornado internal method to subsitute the regexp groups in the rule with some names taken from the handler method function parameters, this internal function has been there since ages so I think it's pretty safe to reuse.

Assisted-by: Cursor

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?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• tox

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

[Copilot]

Pull request overview

This PR reduces Tornado instrumentation cardinality by deriving route-based span names and stable HTTP metric attributes instead of using concrete request paths/query components.

Changes:

• Adds route discovery utilities for Tornado handlers.
• Updates server span naming and stable metric attributes to use http.route.
• Adds test app routes and assertions for parameterized URL behavior and metric attributes.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
instrumentation/opentelemetry-instrumentation-tornado/src/opentelemetry/instrumentation/tornado/_utils.py	Adds route matching and route formatting helpers.
instrumentation/opentelemetry-instrumentation-tornado/src/opentelemetry/instrumentation/tornado/__init__.py	Uses matched routes for span names and stable server metric attributes.
instrumentation/opentelemetry-instrumentation-tornado/tests/tornado_test_app.py	Adds a parameterized test handler and route.
instrumentation/opentelemetry-instrumentation-tornado/tests/test_instrumentation.py	Adds span-name coverage for parameterized routes.
instrumentation/opentelemetry-instrumentation-tornado/tests/test_metrics_instrumentation.py	Adds stable metric attribute assertions for route/query/path handling.
.changelog/4577.fixed	Documents the cardinality fix and stable metric attribute change.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.