# Semantic conventions for RPC metrics LLMS index: [llms.txt](/llms.txt) --- **Status**: [Release Candidate][DocumentStatus], unless otherwise specified The conventions described in this section are RPC specific. When RPC operations occur, measurements about those operations are recorded to instruments. The measurements are aggregated and exported as metrics, which provide insight into those operations. By including RPC properties as attributes on measurements, the metrics can be filtered for finer grain analysis. > [!IMPORTANT] > Existing RPC instrumentations that are using > [v1.37.0 of this document](https://github.com/open-telemetry/semantic-conventions/blob/v1.37.0/docs/rpc/rpc-metrics.md) > (or prior): > > * SHOULD NOT change the version of the RPC conventions that they emit by > default in their existing major version. Conventions include (but are not > limited to) attributes, metric and span names, and unit of measure. > * SHOULD introduce an environment variable `OTEL_SEMCONV_STABILITY_OPT_IN` > in their existing major version as a comma-separated list of category-specific values > (e.g., http, databases, rpc). The list of values includes: > * `rpc` - emit the stable RPC conventions, and stop emitting > the experimental RPC conventions that the instrumentation emitted > previously. > * `rpc/dup` - emit both the experimental and stable RPC conventions, > allowing for a phased rollout of the stable semantic conventions. > * The default behavior (in the absence of one of these values) is to continue > emitting whatever version of the old experimental RPC conventions > the instrumentation was emitting previously. > * Note: `rpc/dup` has higher precedence than `rpc` in case both values are present > * SHOULD maintain (security patching at a minimum) their existing major version > for at least six months after it starts emitting both sets of conventions. > * MAY drop the environment variable in their next major version and emit only > the stable RPC conventions. *Note: RPC server and client metrics are split to allow correlation across client/server boundaries, e.g. Lining up an RPC method latency to determine if the server is responsible for latency the client is seeing.* ## RPC server ### Metric: `rpc.server.call.duration` This metric is [required][MetricRequired]. This metric SHOULD be specified with [`ExplicitBucketBoundaries`](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.50.0/specification/metrics/api.md#instrument-advisory-parameters) of `[ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ]`. | Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations | | -------- | --------------- | ----------- | -------------- | --------- | ------ | | `rpc.server.call.duration` | Histogram | `s` | Measures the duration of an incoming Remote Procedure Call (RPC). [1] | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | **[1]:** When this metric is reported alongside an RPC server span, the metric value SHOULD be the same as the RPC server span duration. **Attributes:** | Key | Stability | [Requirement Level](/docs/specs/semconv/general/attribute-requirement-level/) | Value Type | Description | Example Values | | --- | --- | --- | --- | --- | --- | | [`rpc.system.name`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Required` | string | The Remote Procedure Call (RPC) system. [1] | `grpc`; `dubbo`; `connectrpc` | | [`error.type`](/docs/specs/semconv/registry/attributes/error.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Conditionally Required` If and only if the operation failed. | string | Describes a class of error the operation ended with. [2] | `DEADLINE_EXCEEDED`; `java.net.UnknownHostException`; `-32602` | | [`rpc.method`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Conditionally Required` if available. | string | The fully-qualified logical name of the method from the RPC interface perspective. [3] | `com.example.ExampleService/exampleMethod`; `EchoService/Echo`; `_OTHER` | | [`rpc.response.status_code`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Conditionally Required` if available. | string | Status code of the RPC returned by the RPC server or generated by the client [4] | `OK`; `DEADLINE_EXCEEDED`; `-32602` | | [`server.address`](/docs/specs/semconv/registry/attributes/server.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Opt-In` | string | A string identifying a group of RPC server instances request is sent to. | `example.com`; `10.1.2.80`; `/tmp/my.sock` | | [`server.port`](/docs/specs/semconv/registry/attributes/server.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Opt-In` | int | Server port number. | `80`; `8080`; `443` | **[1] `rpc.system.name`:** The client and server RPC systems may differ for the same RPC interaction. For example, a client may use Apache Dubbo or Connect RPC to communicate with a server that uses gRPC since both protocols provide compatibility with gRPC. **[2] `error.type`:** If the RPC fails with an error before status code is returned, `error.type` SHOULD be set to the exception type (its fully-qualified class name, if applicable) or a component-specific, low cardinality error identifier. If a response status code is returned and status indicates an error, `error.type` SHOULD be set to that status code. Check system-specific conventions for the details on which values of `rpc.response.status_code` are considered errors. The `error.type` value SHOULD be predictable and SHOULD have low cardinality. Instrumentations SHOULD document the list of errors they report. If the request has completed successfully, instrumentations SHOULD NOT set `error.type`. **[3] `rpc.method`:** The method name MAY have unbounded cardinality in edge or error cases. Some RPC frameworks or libraries provide a fixed set of recognized methods for client stubs and server implementations. Instrumentations for such frameworks MUST set this attribute to the original method name only when the method is recognized by the framework or library. When the method is not recognized, for example, when the server receives a request for a method that is not predefined on the server, or when instrumentation is not able to reliably detect if the method is predefined, the attribute MUST be set to `_OTHER`. In such cases, tracing instrumentations MUST also set `rpc.method_original` attribute to the original method value. If the RPC instrumentation could end up converting valid RPC methods to `_OTHER`, then it SHOULD provide a way to configure the list of recognized RPC methods. The `rpc.method` can be different from the name of any implementing method/function. The `code.function.name` attribute may be used to record the fully-qualified method actually executing the call on the server side, or the RPC client stub method on the client side. **[4] `rpc.response.status_code`:** Usually it represents an error code, but may also represent partial success, warning, or differentiate between various types of successful outcomes. Semantic conventions for individual RPC frameworks SHOULD document what `rpc.response.status_code` means in the context of that system and which values are considered to represent errors. --- `error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used. | Value | Description | Stability | | --- | --- | --- | | `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | --- `rpc.system.name` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used. | Value | Description | Stability | | --- | --- | --- | | `connectrpc` | [Connect RPC](https://connectrpc.com/) | ![Development](https://img.shields.io/badge/-development-blue) | | `dubbo` | [Apache Dubbo](https://dubbo.apache.org/) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | `grpc` | [gRPC](https://grpc.io/) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | `jsonrpc` | [JSON-RPC](https://www.jsonrpc.org/) | ![Development](https://img.shields.io/badge/-development-blue) | ## RPC client ### Metric: `rpc.client.call.duration` This metric is [required][MetricRequired]. This metric SHOULD be specified with [`ExplicitBucketBoundaries`](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.50.0/specification/metrics/api.md#instrument-advisory-parameters) of `[ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ]`. | Name | Instrument Type | Unit (UCUM) | Description | Stability | Entity Associations | | -------- | --------------- | ----------- | -------------- | --------- | ------ | | `rpc.client.call.duration` | Histogram | `s` | Measures the duration of an outgoing Remote Procedure Call (RPC). [1] | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | **[1]:** When this metric is reported alongside an RPC client span, the metric value SHOULD be the same as the RPC client span duration. **Attributes:** | Key | Stability | [Requirement Level](/docs/specs/semconv/general/attribute-requirement-level/) | Value Type | Description | Example Values | | --- | --- | --- | --- | --- | --- | | [`rpc.system.name`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Required` | string | The Remote Procedure Call (RPC) system. [1] | `grpc`; `dubbo`; `connectrpc` | | [`error.type`](/docs/specs/semconv/registry/attributes/error.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Conditionally Required` If and only if the operation failed. | string | Describes a class of error the operation ended with. [2] | `DEADLINE_EXCEEDED`; `java.net.UnknownHostException`; `-32602` | | [`rpc.method`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Conditionally Required` if available. | string | The fully-qualified logical name of the method from the RPC interface perspective. [3] | `com.example.ExampleService/exampleMethod`; `EchoService/Echo`; `_OTHER` | | [`rpc.response.status_code`](/docs/specs/semconv/registry/attributes/rpc.md) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | `Conditionally Required` if available. | string | Status code of the RPC returned by the RPC server or generated by the client [4] | `OK`; `DEADLINE_EXCEEDED`; `-32602` | | [`server.address`](/docs/specs/semconv/registry/attributes/server.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Conditionally Required` If available. | string | A string identifying a group of RPC server instances request is sent to. [5] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | | [`server.port`](/docs/specs/semconv/registry/attributes/server.md) | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | `Conditionally Required` if applicable and if `server.address` is set. | int | Server port number. [6] | `80`; `8080`; `443` | **[1] `rpc.system.name`:** The client and server RPC systems may differ for the same RPC interaction. For example, a client may use Apache Dubbo or Connect RPC to communicate with a server that uses gRPC since both protocols provide compatibility with gRPC. **[2] `error.type`:** If the RPC fails with an error before status code is returned, `error.type` SHOULD be set to the exception type (its fully-qualified class name, if applicable) or a component-specific, low cardinality error identifier. If a response status code is returned and status indicates an error, `error.type` SHOULD be set to that status code. Check system-specific conventions for the details on which values of `rpc.response.status_code` are considered errors. The `error.type` value SHOULD be predictable and SHOULD have low cardinality. Instrumentations SHOULD document the list of errors they report. If the request has completed successfully, instrumentations SHOULD NOT set `error.type`. **[3] `rpc.method`:** The method name MAY have unbounded cardinality in edge or error cases. Some RPC frameworks or libraries provide a fixed set of recognized methods for client stubs and server implementations. Instrumentations for such frameworks MUST set this attribute to the original method name only when the method is recognized by the framework or library. When the method is not recognized, for example, when the server receives a request for a method that is not predefined on the server, or when instrumentation is not able to reliably detect if the method is predefined, the attribute MUST be set to `_OTHER`. In such cases, tracing instrumentations MUST also set `rpc.method_original` attribute to the original method value. If the RPC instrumentation could end up converting valid RPC methods to `_OTHER`, then it SHOULD provide a way to configure the list of recognized RPC methods. The `rpc.method` can be different from the name of any implementing method/function. The `code.function.name` attribute may be used to record the fully-qualified method actually executing the call on the server side, or the RPC client stub method on the client side. **[4] `rpc.response.status_code`:** Usually it represents an error code, but may also represent partial success, warning, or differentiate between various types of successful outcomes. Semantic conventions for individual RPC frameworks SHOULD document what `rpc.response.status_code` means in the context of that system and which values are considered to represent errors. **[5] `server.address`:** May contain a DNS name, an endpoint and path in the service registry, local socket name or an IP address. Semantic conventions for individual RPC systems SHOULD document how to populate this attribute. When address is an IP address, instrumentations SHOULD NOT do a reverse DNS lookup to obtain a DNS name and SHOULD set `server.address` to the provided IP address. **[6] `server.port`:** When observed from the client side, and when communicating through an intermediary, `server.port` SHOULD represent the server port behind any intermediaries, for example proxies, if it's available. --- `error.type` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used. | Value | Description | Stability | | --- | --- | --- | | `_OTHER` | A fallback error value to be used when the instrumentation doesn't define a custom value. | ![Stable](https://img.shields.io/badge/-stable-lightgreen) | --- `rpc.system.name` has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used. | Value | Description | Stability | | --- | --- | --- | | `connectrpc` | [Connect RPC](https://connectrpc.com/) | ![Development](https://img.shields.io/badge/-development-blue) | | `dubbo` | [Apache Dubbo](https://dubbo.apache.org/) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | `grpc` | [gRPC](https://grpc.io/) | ![Release Candidate](https://img.shields.io/badge/-rc-mediumorchid) | | `jsonrpc` | [JSON-RPC](https://www.jsonrpc.org/) | ![Development](https://img.shields.io/badge/-development-blue) | [DocumentStatus]: /docs/specs/otel/document-status [MetricRequired]: /docs/specs/semconv/general/metric-requirement-level.md#required