# Semantic Conventions for Kestrel web server metrics **Status**: [Stable][DocumentStatus] This article defines semantic conventions for Kestrel web server. - [Kestrel endpoint](#kestrel-endpoint) - [Metric: `kestrel.active_connections`](#metric-kestrelactive_connections) - [Metric: `kestrel.connection.duration`](#metric-kestrelconnectionduration) - [Metric: `kestrel.rejected_connections`](#metric-kestrelrejected_connections) - [Metric: `kestrel.queued_connections`](#metric-kestrelqueued_connections) - [Metric: `kestrel.queued_requests`](#metric-kestrelqueued_requests) - [Metric: `kestrel.upgraded_connections`](#metric-kestrelupgraded_connections) - [Metric: `kestrel.tls_handshake.duration`](#metric-kestreltls_handshakeduration) - [Metric: `kestrel.active_tls_handshakes`](#metric-kestrelactive_tls_handshakes) ## Kestrel endpoint Kestrel endpoint is represented with [`System.Net.EndPoint`](https://learn.microsoft.com/dotnet/api/system.net.endpoint) class, which does not always provide information about server address or port. Instrumentation supports `IPEndPoint`, `UnixDomainSocketEndPoint`, and `NamedPipeEndPoint` and sets the `server.address`, `server.port` (for IP endpoint), `network.type`, and `network.transport` attributes from the corresponding endpoint on Kestrel metrics. In case instrumentation does not recognize `EndPoint` implementation, it sets the `server.address` attribute to `endpoint.ToString()` value and `network.transport` value to corresponding `endpoint.AddressFamily` property. ## Metric: `kestrel.active_connections` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.active_connections` | UpDownCounter | `{connection}` | Number of connections that are currently active on the server. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [1] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [2] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [3] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [4] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[4]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.connection.duration` this metric SHOULD be specified with [`ExplicitBucketBoundaries`](https://github.com/open-telemetry/opentelemetry-specification/tree/v1.31.0/specification/metrics/api.md#instrument-advisory-parameters) of `[ 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300 ]`. | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.connection.duration` | Histogram | `s` | The duration of connections on the server. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`error.type`](/docs/attributes-registry/error.md) | string | The full name of exception type. [1] | `System.OperationCanceledException`; `Contoso.MyException` | `Conditionally Required` if and only if an error has occurred. |  | | [`network.protocol.name`](/docs/attributes-registry/network.md) | string | [OSI application layer](https://osi-model.com/application-layer/) or non-OSI equivalent. [2] | `http`; `web_sockets` | `Recommended` |  | | [`network.protocol.version`](/docs/attributes-registry/network.md) | string | The actual version of the protocol used for network communication. [3] | `1.1`; `2` | `Recommended` |  | | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [4] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [5] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [6] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [7] | `80`; `8080`; `443` | `Recommended` |  | | [`tls.protocol.version`](/docs/attributes-registry/tls.md) | string | Numeric part of the version parsed from the original string of the negotiated [SSL/TLS protocol version](https://www.openssl.org/docs/man1.1.1/man3/SSL_get_version.html#RETURN-VALUES) | `1.2`; `3` | `Recommended` |  | **[1]:** Captures the exception type when a connection fails. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** If protocol version is subject to negotiation (for example using [ALPN](https://www.rfc-editor.org/rfc/rfc7301.html)), this attribute SHOULD be set to the negotiated version. If the actual protocol version is not known, this attribute SHOULD NOT be set. **[4]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[5]:** The value SHOULD be normalized to lowercase. **[6]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[7]:** 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. |  | `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.rejected_connections` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.rejected_connections` | Counter | `{connection}` | Number of connections rejected by the server. [1] |  | **[1]:** Connections are rejected when the currently active count exceeds the value configured with `MaxConcurrentConnections`. Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [1] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [2] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [3] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [4] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[4]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.queued_connections` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.queued_connections` | UpDownCounter | `{connection}` | Number of connections that are currently queued and are waiting to start. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [1] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [2] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [3] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [4] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[4]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.queued_requests` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.queued_requests` | UpDownCounter | `{request}` | Number of HTTP requests on multiplexed connections (HTTP/2 and HTTP/3) that are currently queued and are waiting to start. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.protocol.name`](/docs/attributes-registry/network.md) | string | [OSI application layer](https://osi-model.com/application-layer/) or non-OSI equivalent. [1] | `http`; `web_sockets` | `Recommended` |  | | [`network.protocol.version`](/docs/attributes-registry/network.md) | string | The actual version of the protocol used for network communication. [2] | `1.1`; `2` | `Recommended` |  | | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [3] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [4] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [5] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [6] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. **[2]:** If protocol version is subject to negotiation (for example using [ALPN](https://www.rfc-editor.org/rfc/rfc7301.html)), this attribute SHOULD be set to the negotiated version. If the actual protocol version is not known, this attribute SHOULD NOT be set. **[3]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[4]:** The value SHOULD be normalized to lowercase. **[5]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[6]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.upgraded_connections` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.upgraded_connections` | UpDownCounter | `{connection}` | Number of connections that are currently upgraded (WebSockets). . [1] |  | **[1]:** The counter only tracks HTTP/1.1 connections. Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [1] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [2] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [3] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [4] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[4]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.tls_handshake.duration` this metric SHOULD be specified with [`ExplicitBucketBoundaries`](https://github.com/open-telemetry/opentelemetry-specification/tree/v1.31.0/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 | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.tls_handshake.duration` | Histogram | `s` | The duration of TLS handshakes on the server. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`error.type`](/docs/attributes-registry/error.md) | string | The full name of exception type. [1] | `System.OperationCanceledException`; `Contoso.MyException` | `Conditionally Required` if and only if an error has occurred. |  | | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [2] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [3] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [4] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [5] | `80`; `8080`; `443` | `Recommended` |  | | [`tls.protocol.version`](/docs/attributes-registry/tls.md) | string | Numeric part of the version parsed from the original string of the negotiated [SSL/TLS protocol version](https://www.openssl.org/docs/man1.1.1/man3/SSL_get_version.html#RETURN-VALUES) | `1.2`; `3` | `Recommended` |  | **[1]:** Captures the exception type when a TLS handshake fails. **[2]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[3]:** The value SHOULD be normalized to lowercase. **[4]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[5]:** 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. |  | `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | ## Metric: `kestrel.active_tls_handshakes` | Name | Instrument Type | Unit (UCUM) | Description | Stability | | -------- | --------------- | ----------- | -------------- | --------- | | `kestrel.active_tls_handshakes` | UpDownCounter | `{handshake}` | Number of TLS handshakes that are currently in progress on the server. [1] |  | **[1]:** Meter name: `Microsoft.AspNetCore.Server.Kestrel`; Added in: ASP.NET Core 8.0 | Attribute | Type | Description | Examples | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability | |---|---|---|---|---|---| | [`network.transport`](/docs/attributes-registry/network.md) | string | [OSI transport layer](https://osi-model.com/transport-layer/) or [inter-process communication method](https://wikipedia.org/wiki/Inter-process_communication). [1] | `tcp`; `unix` | `Recommended` |  | | [`network.type`](/docs/attributes-registry/network.md) | string | [OSI network layer](https://osi-model.com/network-layer/) or non-OSI equivalent. [2] | `ipv4`; `ipv6` | `Recommended` if the transport is `tcp` or `udp` |  | | [`server.address`](/docs/attributes-registry/server.md) | string | Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [3] | `example.com`; `10.1.2.80`; `/tmp/my.sock` | `Recommended` |  | | [`server.port`](/docs/attributes-registry/server.md) | int | Server port number. [4] | `80`; `8080`; `443` | `Recommended` |  | **[1]:** The value SHOULD be normalized to lowercase. Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345. **[2]:** The value SHOULD be normalized to lowercase. **[3]:** When observed from the client side, and when communicating through an intermediary, `server.address` SHOULD represent the server address behind any intermediaries, for example proxies, if it's available. **[4]:** 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. `network.transport` 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 | |---|---|---| | `tcp` | TCP |  | | `udp` | UDP |  | | `pipe` | Named or anonymous pipe. |  | | `unix` | Unix domain socket |  | `network.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 | |---|---|---| | `ipv4` | IPv4 |  | | `ipv6` | IPv6 |  | [DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/tree/v1.31.0/specification/document-status.md