A109: Target Attribute Filter for OpenTelemetry Metrics#528
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kannanjgithub
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Jan 9, 2026
Introduce an optional Predicate<String> targetAttributeFilter to control how grpc.target is recorded in OpenTelemetry client metrics. When a filter is provided, targets rejected by the predicate are normalized to "other" to reduce grpc.target metric cardinality, while accepted targets are recorded as-is. If no filter is set, existing behavior is preserved. This change adds a new Builder API on GrpcOpenTelemetry to allow applications to configure the filter. Tests verify both the Builder wiring and the target normalization behavior. This is an optional API; annotation (e.g., experimental) can be added per maintainer guidance. Refs #12322 Related: gRFC A109 – Target Attribute Filter for OpenTelemetry Metrics grpc/proposal#528
jdcormie
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Feb 11, 2026
Introduce an optional Predicate<String> targetAttributeFilter to control how grpc.target is recorded in OpenTelemetry client metrics. When a filter is provided, targets rejected by the predicate are normalized to "other" to reduce grpc.target metric cardinality, while accepted targets are recorded as-is. If no filter is set, existing behavior is preserved. This change adds a new Builder API on GrpcOpenTelemetry to allow applications to configure the filter. Tests verify both the Builder wiring and the target normalization behavior. This is an optional API; annotation (e.g., experimental) can be added per maintainer guidance. Refs grpc#12322 Related: gRFC A109 – Target Attribute Filter for OpenTelemetry Metrics grpc/proposal#528
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Hello @ejona86 and @markdroth, could you help route this gRFC to an APPROVER? I updated the proposal to narrow the scope based on grpc/grpc-java#12322:
Could you advise whether this framing is appropriate, and whether this should remain A109, be handled as an A66/A96 update, or be converted to a Java-specific proposal? Once an APPROVER is assigned, I will send the required grpc-io notification and update the |
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Summary
This gRFC proposes an optional Java API for controlling how
grpc.targetis recorded in gRPC Java OpenTelemetry client metrics. Targets accepted by the filter are recorded as-is; rejected targets are recorded as"other"to reduce metric cardinality while preserving existing behavior by default.Background
This addresses the concrete Java cardinality issue reported in grpc/grpc-java#12322, where clients connecting to thousands of targets can exceed OpenTelemetry cardinality limits for
grpc.client.*metrics.The Java implementation has already been reviewed and merged in grpc/grpc-java#12587.
Scope
This proposal is scoped to Java OpenTelemetry client metrics covered by A66/A96. It does not change channel behavior, target resolution, OpenTelemetry View behavior, or the deprecated C++ target filter API.
The deprecated C++
SetTargetAttributeFilterAPI is described only as related history.