Expose baggage in log4j context data when there is no current span

[trask]

Found while reviewing #19375.

When otel.instrumentation.log4j-context-data.add-baggage=true, the log4j instrumentation silently drops baggage if there is no valid current span:

• OpenTelemetryContextDataProvider (2.17) returns early on !spanContext.isValid(), before the baggage block
• SpanDecoratingContextDataInjector (2.7) does the same

The logback MDC instrumentation does not — in both OpenTelemetryAppender.processEvent() and LoggingEventInstrumentation, isValid() only guards the trace/span/flags entries, and baggage is added unconditionally. AbstractLogbackTest.testNoIdsWhenNoSpan already asserts baggage is present outside a span.

This aligns log4j with logback: the span validity check now guards only the trace id / span id / trace flags entries, and the early return happens only when there is neither a valid span nor any baggage (preserving the existing fast path).

Pre-existing since #8810 (2023), which added baggage support inside the region guarded by an early return introduced back in #4957.

Testing: Log4j2Test.testNoIdsWhenNoSpan now runs inside a baggage scope and asserts the baggage. entry, mirroring the logback test. Verified it fails on both modules without the fix.

[opentelemetry-pr-dashboard]

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Merged · refreshed 2026-08-04 11:49 UTC

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[Copilot]

Pull request overview

Aligns Log4j context-data instrumentation with Logback by retaining baggage when no valid span exists.

Changes:

• Restricts span validity checks to trace identifiers.
• Preserves the empty-context fast path.
• Tests baggage propagation outside spans.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
Log4j2Test.java	Tests baggage without an active span.
SpanDecoratingContextDataInjector.java	Propagates baggage independently of span validity.
OpenTelemetryContextDataProvider.java	Updates library-mode context data propagation.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (2)

instrumentation/log4j/log4j-context-data/log4j-context-data-2.17/library-autoconfigure/src/main/java/io/opentelemetry/instrumentation/log4j/contextdata/v2_17/OpenTelemetryContextDataProvider.java:70

• When baggage is present but baggage export is disabled (the default), this guard now falls through, initializes Configuration, and allocates a HashMap for every no-span log event although nothing will be added. Keep the empty-baggage check first to retain the restored lazy-initialization behavior, but also return early when the feature is disabled.

    if (!spanContext.isValid() && baggage.isEmpty()) {

instrumentation/log4j/log4j-context-data/log4j-context-data-2.7/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/log4j/contextdata/v2_7/SpanDecoratingContextDataInjector.java:54

• When baggage is present but add-baggage remains at its default false, this guard now falls through and copies the StringMap for every no-span log event even though no dynamic value can be added. Since this injector is on the logging hot path, include BAGGAGE_ENABLED in the fast-path condition so disabled baggage preserves the prior allocation behavior.

    if (!currentContext.isValid() && baggage.isEmpty()) {

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (1)

instrumentation/log4j/log4j-context-data/log4j-context-data-2.7/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/log4j/contextdata/v2_7/SpanDecoratingContextDataInjector.java:54

• [Performance] Baggage.fromContext(context) now runs for every Log4j event even when baggage injection is disabled (the default), adding an avoidable context lookup on the logging hot path. Since BAGGAGE_ENABLED is already a static value in this implementation, check it before reading baggage.

    Baggage baggage = Baggage.fromContext(context);
    boolean addBaggage = BAGGAGE_ENABLED && !baggage.isEmpty();

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.