Semantic Conventions for HTTP Metrics

Status: Experimental, partial feature-freeze

The conventions described in this section are HTTP specific. When HTTP operations occur, metric events about those operations will be generated and reported to provide insight into the operations. By adding HTTP attributes to metric events it allows for finely tuned filtering.

Disclaimer: These are initial HTTP metric instruments and attributes but more may be added in the future.

HTTP Server
HTTP Client

Warning Existing HTTP instrumentations that are using v1.20.0 of this document (or prior):

SHOULD NOT change the version of the HTTP or networking conventions that they emit until the HTTP semantic conventions are marked stable (HTTP stabilization will include stabilization of a core set of networking conventions which are also used in HTTP instrumentations). 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 the existing major version which is a comma-separated list of values. The only values defined so far are:

http - emit the new, stable HTTP and networking conventions, and stop emitting the old experimental HTTP and networking conventions that the instrumentation emitted previously.

http/dup - emit both the old and the stable HTTP and networking conventions, allowing for a seamless transition.

The default behavior (in the absence of one of these values) is to continue emitting whatever version of the old experimental HTTP and networking conventions the instrumentation was emitting previously.

Note: http/dup has higher precedence than http in case both values are present

SHOULD maintain (security patching at a minimum) the existing major version for at least six months after it starts emitting both sets of conventions.

SHOULD drop the environment variable in the next major version (stable next major version SHOULD NOT be released prior to October 1, 2023).

HTTP Server

Metric: `http.server.request.duration`

Status: Experimental, Feature-freeze

This metric is required.

When this metric is reported alongside an HTTP server span, the metric value SHOULD be the same as the HTTP server span duration.

This metric SHOULD be specified with ExplicitBucketBoundaries of [ 0, 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
`http.server.request.duration`	Histogram	`s`	Measures the duration of inbound HTTP requests.

Attribute	Type	Description	Examples	Requirement Level
`http.route`	string	The matched route (path template in the format used by the respective server framework). See note below [1]	`/users/:userID?`; `{controller}/{action}/{id?}`	Conditionally Required: If and only if it's available
`error.type`	string	Describes a class of error the operation ended with. [2]	`timeout`; `name_resolution_error`; `500`	Conditionally Required: If request has ended with an error.
`http.request.method`	string	HTTP request method. [3]	`GET`; `POST`; `HEAD`	Required
`http.response.status_code`	int	HTTP response status code.	`200`	Conditionally Required: If and only if one was received/sent.
`network.protocol.name`	string	OSI Application Layer or non-OSI equivalent. The value SHOULD be normalized to lowercase.	`amqp`; `http`; `mqtt`	Recommended
`network.protocol.version`	string	Version of the application layer protocol used. See note below. [4]	`3.1.1`	Recommended
`server.address`	string	Name of the local HTTP server that received the request. [5]	`example.com`	Opt-In
`server.port`	int	Port of the local HTTP server that received the request. [6]	`80`; `8080`; `443`	Opt-In
`url.scheme`	string	The URI scheme component identifying the used protocol.	`http`; `https`	Required

[1]: MUST NOT be populated when this is not supported by the HTTP server framework as the route attribute should have low-cardinality and the URI path can NOT substitute it. SHOULD include the application root if there is one.

[2]: If the request fails with an error before response status code was sent or received, error.type SHOULD be set to exception type or a component-specific low cardinality error code.

If response status code was sent or received and status indicates an error according to HTTP span status definition, error.type SHOULD be set to the string representation of the status code, an exception type (if thrown) or a component-specific error code.

The error.type value SHOULD be predictable and SHOULD have low cardinality. Instrumentations SHOULD document the list of errors they report.

The cardinality of error.type within one instrumentation library SHOULD be low, but telemetry consumers that aggregate data from multiple instrumentation libraries and applications should be prepared for error.type to have high cardinality at query time, when no additional filters are applied.

If the request has completed successfully, instrumentations SHOULD NOT set error.type.

[3]: HTTP request method value SHOULD be "known" to the instrumentation. By default, this convention defines "known" methods as the ones listed in RFC9110 and the PATCH method defined in RFC5789.

If the HTTP request method is not known to instrumentation, it MUST set the http.request.method attribute to _OTHER.

If the HTTP instrumentation could end up converting valid HTTP request methods to _OTHER, then it MUST provide a way to override the list of known HTTP methods. If this override is done via environment variable, then the environment variable MUST be named OTEL_INSTRUMENTATION_HTTP_KNOWN_METHODS and support a comma-separated list of case-sensitive known HTTP methods (this list MUST be a full override of the default known method, it is not a list of known methods in addition to the defaults).

HTTP method names are case-sensitive and http.request.method attribute value MUST match a known HTTP method name exactly. Instrumentations for specific web frameworks that consider HTTP methods to be case insensitive, SHOULD populate a canonical equivalent. Tracing instrumentations that do so, MUST also set http.request.method_original to the original value.

[4]: network.protocol.version refers to the version of the protocol used and might be different from the protocol client's version. If the HTTP client used has a version of 0.27.2, but sends HTTP version 1.1, this attribute should be set to 1.1.

[5]: Determined by using the first of the following that applies

The primary server name of the matched virtual host. MUST only include host identifier.
Host identifier of the request target if it's sent in absolute-form.
Host identifier of the Host header

SHOULD NOT be set if only IP address is available and capturing name would require a reverse DNS lookup.

[6]: Determined by using the first of the following that applies

Port identifier of the primary server host of the matched virtual host.
Port identifier of the request target if it's sent in absolute-form.
Port identifier of the Host header

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
`_OTHER`	A fallback error value to be used when the instrumentation does not define a custom value for it.

http.request.method 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
`CONNECT`	CONNECT method.
`DELETE`	DELETE method.
`GET`	GET method.
`HEAD`	HEAD method.
`OPTIONS`	OPTIONS method.
`PATCH`	PATCH method.
`POST`	POST method.
`PUT`	PUT method.
`TRACE`	TRACE method.
`_OTHER`	Any HTTP method that the instrumentation has no prior knowledge of.

Metric: `http.server.active_requests`

Status: Experimental

This metric is optional.

Name	Instrument Type	Unit (UCUM)	Description
`http.server.active_requests`	UpDownCounter	`{request}`	Measures the number of concurrent HTTP requests that are currently in-flight.

Attribute	Type	Description	Examples	Requirement Level
`http.request.method`	string	HTTP request method. [1]	`GET`; `POST`; `HEAD`	Required
`server.address`	string	Name of the local HTTP server that received the request. [2]	`example.com`	Opt-In
`server.port`	int	Port of the local HTTP server that received the request. [3]	`80`; `8080`; `443`	Opt-In
`url.scheme`	string	The URI scheme component identifying the used protocol.	`http`; `https`	Required

[1]: HTTP request method value SHOULD be "known" to the instrumentation. By default, this convention defines "known" methods as the ones listed in RFC9110 and the PATCH method defined in RFC5789.

If the HTTP request method is not known to instrumentation, it MUST set the http.request.method attribute to _OTHER.

If the HTTP instrumentation could end up converting valid HTTP request methods to _OTHER, then it MUST provide a way to override the list of known HTTP methods. If this override is done via environment variable, then the environment variable MUST be named OTEL_INSTRUMENTATION_HTTP_KNOWN_METHODS and support a comma-separated list of case-sensitive known HTTP methods (this list MUST be a full override of the default known method, it is not a list of known methods in addition to the defaults).

HTTP method names are case-sensitive and http.request.method attribute value MUST match a known HTTP method name exactly. Instrumentations for specific web frameworks that consider HTTP methods to be case insensitive, SHOULD populate a canonical equivalent. Tracing instrumentations that do so, MUST also set http.request.method_original to the original value.

[2]: Determined by using the first of the following that applies

The primary server name of the matched virtual host. MUST only include host identifier.
Host identifier of the request target if it's sent in absolute-form.
Host identifier of the Host header

SHOULD NOT be set if only IP address is available and capturing name would require a reverse DNS lookup.

[3]: Determined by using the first of the following that applies

Port identifier of the primary server host of the matched virtual host.
Port identifier of the request target if it's sent in absolute-form.
Port identifier of the Host header

http.request.method 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
`CONNECT`	CONNECT method.
`DELETE`	DELETE method.
`GET`	GET method.
`HEAD`	HEAD method.
`OPTIONS`	OPTIONS method.
`PATCH`	PATCH method.
`POST`	POST method.
`PUT`	PUT method.
`TRACE`	TRACE method.
`_OTHER`	Any HTTP method that the instrumentation has no prior knowledge of.

Metric: `http.server.request.size`

Status: Experimental

This metric is optional.

Name	Instrument Type	Unit (UCUM)	Description
`http.server.request.size`	Histogram	`By`	Measures the size of HTTP request messages. [1]

[1]: Size as measured over the wire (compressed size if messages are compressed).

Attribute	Type	Description	Examples	Requirement Level
`http.route`	string	The matched route (path template in the format used by the respective server framework). See note below [1]	`/users/:userID?`; `{controller}/{action}/{id?}`	Conditionally Required: If and only if it's available
`error.type`	string	Describes a class of error the operation ended with. [2]	`timeout`; `name_resolution_error`; `500`	Conditionally Required: If request has ended with an error.
`http.request.method`	string	HTTP request method. [3]	`GET`; `POST`; `HEAD`	Required
`http.response.status_code`	int	HTTP response status code.	`200`	Conditionally Required: If and only if one was received/sent.
`network.protocol.name`	string	OSI Application Layer or non-OSI equivalent. The value SHOULD be normalized to lowercase.	`amqp`; `http`; `mqtt`	Recommended
`network.protocol.version`	string	Version of the application layer protocol used. See note below. [4]	`3.1.1`	Recommended
`server.address`	string	Name of the local HTTP server that received the request. [5]	`example.com`	Opt-In
`server.port`	int	Port of the local HTTP server that received the request. [6]	`80`; `8080`; `443`	Opt-In
`url.scheme`	string	The URI scheme component identifying the used protocol.	`http`; `https`	Required