[opentelemetry-sdk] Fix overwriting of the service.instance.id which has been populated through the resource detectors

[rads-1996]

Description

Prevent ServiceInstanceIdResourceDetector from overwriting an existing service.instance.id set by another resource detector(ex. Azure) or user configuration. Add regression coverage for detector-, initial-resource-, and environment-provided IDs, while retaining UUID generation when no ID is present.

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

• Unit tests for opentelemetry-sdk
• E2E application has been tested to ensure the relevant service instance id is populated

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

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

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on the author · refreshed 2026-09-22 15:25 UTC

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• Top-level threads: 1

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[Shriprasad-P]

Thanks for the PR. Approach looks sensible — please confirm edge cases and failure paths are covered by tests.

[Copilot]

Copilot review overview

🟡 Changes recommended

Explicit detector ordering and fork-time resource refresh can still overwrite configured IDs, and direct user/environment precedence lacks coverage.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2 · 1

Open (3)

• Preserve explicit service instance IDs after fork · New
• Preserve explicit service_instance detector ordering · New
• Test service instance ID priority from resources and environment · New

What changed in this PR

This PR adjusts resource detector ordering to prevent generated service.instance.id values from overriding configured detector values.

Changes:

• Prepends the service-instance detector.
• Adds detector regression tests.
• Adds a changelog entry.

File	Description
opentelemetry-sdk/​src/​opentelemetry/​sdk/​resources/​__init__.py	Changes detector ordering.
opentelemetry-sdk/​tests/​resources/​test_resources.py	Adds service-instance regression tests.
.changelog/​5660.fixed	Documents the fix.

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