AGENTS.md

1# Backend Metrics Filter
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3This directory contains a server-side filter for reporting backend metrics.
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5## Overarching Purpose
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7The filter provides a mechanism to collect backend metric data, serialize it, and send it as trailing metadata in a gRPC call. This data can be used by clients to make load balancing decisions.
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9## Files
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11*   `backend_metric_filter.h`, `backend_metric_filter.cc`: These files define the `BackendMetricFilter` class, a server-side channel filter that retrieves backend metrics from a `BackendMetricProvider`, serializes them using the `xds.data.orca.v3.OrcaLoadReport` protobuf message, and attaches the result to the server's trailing metadata. The filter is activated by the `GRPC_ARG_SERVER_CALL_METRIC_RECORDING` channel argument.
12*   `backend_metric_provider.h`: This file defines the `BackendMetricProvider` interface, which is responsible for providing the backend metric data to the filter.
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14## Major Classes
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16*   `grpc_core::BackendMetricFilter`: The channel filter implementation.
17*   `grpc_core::BackendMetricProvider`: An interface for a class that can provide backend metric data.
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19## Notes
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21*   This filter is a key component of gRPC's custom load balancing support. It allows backends to provide real-time load information to clients, enabling more intelligent load balancing decisions.
22*   The filter is configured to run on the server and is only active when the appropriate channel argument is set.
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