[FEATURE]: Allow keeping version tag even if dd_service is not applied

[joelim41]

Gem Name

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Gem Version(s)

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Describe the goal of the feature

#4027 - this change removes the version tag for spans that are not using the default service name. We would like to have an option to opt out of this change to maintain the old behavior. It mentions that this is done to have parity with other tracing clients, can someone elaborate more on this?

Is your feature request related to a problem?

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Describe alternatives you've considered

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Additional context

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How does Datadog help you?

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[mabdinur]

Hi @joelim41,

This behavior has evolved over several versions of ddtrace.

In ddtrace < 2.5:

• If DD_VERSION was set, the version tag was applied to all spans, regardless of the service name.

In ddtrace 2.5–2.7:

• Due to PR #4027, DD_VERSION was applied only if the span’s service matched the global service name and that global service name was not the default value. This introduced a bug where DD_VERSION was inconsistently applied.

In ddtrace ≥ 2.8:

• This behavior was corrected in PR #4075. Now, DD_VERSION is applied only if:
  • The span’s service matches the global service name.
  • The global service name is not a default value.
• If a custom service name is used for a span, the global version tag is no longer applied, users must explicitly set the version tag for that span.

The rationale for this change is to ensure consistency in service and version tags across tracers (Unified Service Tagging). When a custom service name is specified, the corresponding version tag should also be set manually.

For users who prefer the legacy behavior (applying DD_VERSION to all spans), we recommend using a span processor to manually apply the version tag as needed.