feat: Add system property override for service.instance.id

[kuisathaverat]

Summary

Add ability to override service.instance.id via system property for CloudBees CI high availability scenarios where multiple controller replicas need unique instance identifiers.

Changes

• UPDATE: JenkinsOpenTelemetryPluginConfiguration.java

  • Add system property check: io.jenkins.plugins.opentelemetry.service.instance.id
  • Fall back to Jenkins.getLegacyInstanceId() when property not set
  • Maintain 100% backward compatibility

• NEW: ServiceInstanceIdConfigurationTest.java

  • Integration test for default behavior (backward compatibility)
  • Integration test for system property override
  • Edge case tests (empty string, whitespace-only values)
  • Uses Jenkins Test Harness and InMemoryMetricExporter

Testing

• 4 integration tests using Jenkins Test Harness
• Tests validate both default and override behaviors
• Edge cases covered (empty/whitespace values)

Additional Information

• Property name: io.jenkins.plugins.opentelemetry.service.instance.id
• Usage: Set via JVM system property (e.g., -Dio.jenkins.plugins.opentelemetry.service.instance.id=replica-01)
• No configuration UI changes needed
• No breaking changes

Closes #1154

[Copilot]

Pull request overview

This PR adds the ability to override service.instance.id via a system property (io.jenkins.plugins.opentelemetry.service.instance.id) to support CloudBees CI high availability scenarios where multiple controller replicas require unique instance identifiers while maintaining the same service name.

Changes:

• Added system property check with fallback to Jenkins.getLegacyInstanceId() for backward compatibility
• Created integration tests to validate default behavior, system property override, and edge cases

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 12 comments.

File	Description
src/main/java/io/jenkins/plugins/opentelemetry/JenkinsOpenTelemetryPluginConfiguration.java	Adds system property check for service.instance.id with proper validation and fallback logic
src/test/java/io/jenkins/plugins/opentelemetry/ServiceInstanceIdConfigurationTest.java	New test file with integration tests (contains multiple critical issues preventing compilation)

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[Copilot]

The test uses @WithJenkins annotation from JUnit Jupiter (org.jvnet.hudson.test.junit.jupiter.WithJenkins), but this is inconsistent with the rest of the test suite which uses JUnit 4 with @rule or @ClassRule JenkinsRule patterns. Looking at BaseIntegrationTest.java:77-79 and OtelLocaLogMirroringTest.java:36-37, the established pattern is to use JenkinsConfiguredWithCodeRule or JenkinsRule with JUnit 4 annotations. This test should follow the same pattern to ensure it integrates properly with the existing test infrastructure.

[Copilot]

The assertion assertThat("Metrics list should not be empty", !metrics.isEmpty()) is syntactically incorrect for Hamcrest. The correct form should be assertThat("Metrics list should not be empty", metrics, is(not(empty()))) or simply check the condition with a standard assertion. The current form passes a boolean as the actual value instead of using a proper Hamcrest matcher.

[ArpanC6]

Great addition @kuisathaverat! The system property override approach for
CloudBees CI HA scenarios is clean and maintains full backward compatibility.

A few observations after reviewing the changes:

1. Branch out-of-date — The branch is currently behind main. A rebase
   might be worth doing before final review to ensure no merge conflicts with
   recent changes.

2. JUnit 5 migration — I can see the test was moved to JUnit 5
   (@WithJenkins) via commit de7630b to address Copilot's feedback about
   consistency. This looks good now.

3. Edge case consideration — The tests cover empty string and
   whitespace-only values, which is thorough. One additional edge case worth
   considering: what happens if the system property is set to a value
   containing only special characters or exceeds a reasonable length limit?
   A validation or trim + length check in the property reading logic could
   make this more robust.

4. Documentation — Would it be worth adding a note to the plugin wiki
   or README about this new system property
   (io.jenkins.plugins.opentelemetry.service.instance.id) for operators
   managing CloudBees CI HA deployments?